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Online Radio Archive For Schools And Radio Amateurs

Information Log A01- Introduction For Radio Amateurs

you've heard the term "ham radios" and were confused by the meaning, you aren't alone. Ham radio is another way of saying amateur radio as the person who broadcasts over the frequency is referred to as a "ham". Don't let the term amateur fool you - many ham radio operators have years of experience in the hobby and can hardly be considered novices. In the case of ham radio, the term amateur simply refers to the designated radio frequencies used in the radio community. The radio frequencies used are non-commercial bands, reserved solely for the enthusiast. In order to operate ham radio equipment and communicate with other participants over amateur radio frequencies, a ham must become licensed.

History of Ham Radio

Ham radio enjoys a lengthy history dating back to the early twentieth century. With a global audience, amateur radio enthusiasts are part of a community that has made significant contributions to many fields. It is known that as far back as 1909, 89 radio call stations had been designated for amateur or ham radio use. Ham radio has become a universal phenomenon, with no signs of slowing down. From computer networking to monitoring disasters or simply as a form of wireless communication within the community, ham radio has proved it is here to stay.

Ham Radio Equipment

In order to operate as a ham you need the right equipment. Ham radio equipment has changed over the years, and as more ways to communicate are developed, the equipment used changes. For instance, voice over internet protocol (VoIP) has enabled new types of ham radio equipment. For those interested in becoming a ham, the decision must be made as to what type of frequency or communication method you will use. The best ham radio equipment for you will depend on what type of communication method you decide on.

Ham radio equipment typically includes a radio and transceiver (handheld, mobile, or mounted). Depending upon your goals, you may choose to add computers, power cables, antennas, weather stations, scanners and receivers, towers, two-way radios, and other specialized devices. Determine your end goals to ensure you select the best equipment for your needs. The equipment you select is imperative to your success as an operator. Choose your radio equipment wisely, as it can be a significant investment. Look for ham radios for beginners or used equipment when you're just starting out to get a feel for the hobby without as large of an investment.

Terminology for Ham Radio

As with any hobby, the ham radio community uses their own terminology and lingo. Those participating in amateur radio will find that it is invaluable to spend time understanding various terms used by fellow hobbyists. While some words pertain to the science behind radio, there are other slang words that the enthusiasts have adopted over the years. Understanding the terminology associated with ham radio will not only help you communicate more effectively with other enthusiasts; but will also help you understand the best way to operate your radio equipment.

How to use Call Signs

A call sign is the alphanumerical code given to licensed ham radio operators so they are legally recognized as amateur radio operators. Call signs vary in length, but it's common to find that those with shorter call signs have greater flexibility as radio operators. Different governing bodies assign call signs worldwide. In the United States, the Federal Communications Commission (FCC) assigns amateur or ham radio call signs. A licensed radio operator must use his or her assigned call sign every time he or she transmits.

Ham Radio Organizations and Licensing

Organizations and licensing are two important factors to consider in the ham radio community. All ham radio operators need to be licensed in order to broadcast. However, amateur radio incorporates a global community and there are different licensing procedures for each country. Joining organizations is an excellent way to stay current with the latest rules, regulations, and trends as well. Some organizations obtain call signs, making them their own closely-knit group of radio operators.

In addition to nationwide organizations, ham radio enthusiasts may find that joining a ham radio organization is the best way to connect with others, especially if they don't know someone that is already in the amateur radio community. There are national as well as local clubs that will make communication easy between hobbyists. The person new to ham radio may find that the best way to familiarize him or herself with the hobby or to find a ham radio guide is by networking with others through organizations. Several popular organizations in the United States and abroad include the National Association for Amateur Radio and the International Amateur Radio Union. You may find more resources for ham radio enthusiasts, including information on beginning, ham radio terms and lingo, and the many uses of amateur radio in the links below.

Information Log A02-Morse Code

Information Log A03-Building your own Radio

Are you a bit loose on the cash, and need more to buy your radio? No problem! Make your own. Here is a list of products and how to make your very own D.I.Y Radio!

Magnet wire: Electronics supply stores often sell a set, for about $10, that comes with 40 feet of 22-gauge, 75 feet of 26-gauge and 200 feet of 30-gauge magnet wire. You can also find it at Amazon.com or Radioshack.com.

1 set of alligator leads with clips at each end.

1 diode: Look for IN34A diodes, also called “germanium diodes,” at an electronics supply store or online.

1 glue stick or anything similar in size — about 1 inch by 1 inch by 6 inches. It can be a piece of wood. It doesn’t have to be perfectly round, but using something round is easier for winding.

Electrical tape

Wire stripping pliers

Telephone handset with cord. If you don’t have an old phone that you don’t use anymore, you might be able to find one at thrift stores or garage sales.

One board for mounting your radio — 2 feet by 2 feet will work. You can make the radio without this, but having a workspace and a place to mount the radio makes it easier to carry around while you’re looking for a place to hook the ground wire.

Step 1: Wind 26-gauge wire (the green magnet wire) around the glue stick until it covers nearly the entire cylinder. Keep the wire tight. Leave about six inches of wire on each end. Once you’re finished winding it, tape around both ends of the cylinder to make sure the wire holds. Then, mount the coil to the board with electrical tape.

Step 2: Strip the ends of the wire you’ve left from each end of the coil. Use wire stripping pliers or sandpaper. The wire is very thin. Removing the enamel and exposing about one inch of the wire should be easy.

Step 3: Attach the wire from the right side of the coil to one end of your diode. Tape the connection.

Step 4: Cut the end of the phone cord and strip about two inches of it. It should expose two wires. Strip those wires. Take your time; this wire is thin. (Try this tip: Before hooking up the tiny telephone cord wires, get some thicker insulated magnet wire and tape about two inches to each wire. This will make the rest of the job easier.) Attach one end of the wire to the exposed end of the diode. Tape that connection.

If your phone cord has four wires instead of two, you have to figure out which two will work. Take a 9-volt battery and place one cord against the positive (+) pole of the battery and another cord on the negative (-). When you find a combination that makes a clicking sound in the headset, you have found the two wires to use.

Step 5: Connect the second telephone wire to the green wire coming from the left side of the coil. Before taping this connection, clip one of the alligator leads to it. Tape those three wires together — the alligator lead (that’s your ground wire), the telephone wire and the wire coming from the left side of the coil.

Step 6: Make your antenna by clipping one of the remaining alligator lead wires to one end of the 22-gauge magnet wire. Leave this wire on its roll.

Step 7: Scrape a thin strip of enamel from the wire wrapped around the glue stick. You can do this with any sharp object or a piece of sandpaper.

SEE IF IT WORKS

Attach your telephone cord to its handset.

Find a good ground for the alligator wire that’s connected to the left side of your coil. A pipe going into the ground is perfect.

Unroll the antenna wire and hang it over a tree branch with help from an adult.

Touch the alligator clip that leads to your antenna wire to the top of the coil. You should be able to hear an AM radio signal.

TROUBLESHOOTING

If you can’t get any signal, it’s probably your ground wire. With permission from an adult, unscrew one bolt that holds the faceplate to a light switch or outlet. Unscrew it just enough to hook your alligator clip. Don’t remove the plat.

If you get a weak signal, it’s your antenna. If your parents have an old television antenna, hook your radio antenna wire to one of the connections on the TV antenna wire instead of running wire up a tree.

Information Log A04- Raspberry Pi-Rate Method

TIRED OF THE preprogramed junk that makes up radio? Don’t curse the DJ; seize the airwaves! An FM transmitter (like this one) is a simple device that connects to your music player and broadcasts your tunes through a weak radio signal. This signal can be picked up by receivers in the immediate vicinity, but with a few tweaks you can strengthen it and reach up to 100 feet. Although it may not be much, it can turn your car into a vehicle that doubles as a mobile radio station.

Here’s what to do:

You’ll need

• FM radio transmitter

• Putty knife

• Telescoping antenna (no more than 35 inches long.

• Soldering iron

• Copper wire

Open up the transmitter

Locate the seam on the transmitter's case and pry it open with a putty knife (if your transmitter is screwed shut, you'll need a screwdriver to open it). Be careful to preserve the device's electronics. Once the transmitter is open, locate the antenna. Antennas may vary depending on the type of transmitter you are using. Sometimes the antenna looks like a small metal stick, sometimes it is a wire, but in most cases it's labeled “ANT."

Replace the antenna

Remove the antenna and solder the telescoping antenna in its place. The new antenna might not fit in the transmitter's original casing, so make a hole for the protruding antenna, or create a new case (something like an Altoids tin should do the trick). There are plenty of cheap antennas out there that will work, just make sure that your new antenna is no more than 35 inches long. If your antenna is too long, the signal will be outside of the standard FM transmission spectrum. You want to ensure that anyone with a radio receiver can tune in.

Remove resistors

Many FM transmitters have a resistor (typically marked with an “R”) to limit the power of the signal. Since the goal of this project is to boost signal, you'll want to remove any resistors you find. By simply replacing any resistor with copper wire, you can increase the radio signal even further.

Pick your device

Next you'll want to choose a frequency on the transmitter and the device you want to broadcast from. The device you can use and what frequency the transmitter broadcasts varies from model to model, so you'll need to familiarize yourself with the built in specs beforehand. When you have this figured out, you can begin making your broadcast playlist or personal podcasts.

Test it out

Once your modified transmitter is put together it should be able to send out radio waves, but before you go live you'll want to check. Connect the transmitter to your device and turn them both on. Then tune your radio receiver to the frequency on the transmitter. If you did everything correctly, you should hear the audio that is playing on your connected device. To test the broadcast radius move your transmitter farther and farther away from your receiver, once the audio starts fading out, you have found the transmitter's limit.

Go live

Slap a bumper sticker on your ride advertising your station’s frequency. That way nearby cars will know what frequency to tune into to hear your broadcast. Soon you’ll build a grateful audience of fellow commuters suffering through that traffic jam. Or maybe you can tell the car tailgating you to back off.

Information Log A05- More Radio Building Stuff

The crystal radio gets its name from the galena crystal (lead sulfide) used to rectify the signals. A "cat's whisker" wire contact was moved about the surface of the crystal until a diode junction was formed. The 1N34A germanium diode is the modern substitute for galena and most other germanium small-signal diodes will also work well. Silicon diodes are not a good choice because their much higher barrier potential requires larger signals for efficient rectification. Certain silicon Schottky diodes with low barrier potential will work well but most small-signal Schottky diodes will not perform as well as a garden-variety germanium diode.

The circuit is quite simple but many pitfalls await the novice. The first precaution is most important! The crystal radio works best with a long, high outdoor antenna but the beginner may not fully appreciate the danger of bringing such a wire into the house. Lightning strikes to the antenna will probably destroy the crystal radio but if precautions are not taken, much more damage will result. The best strategy is to incorporate a commercial lightning arrestor with a straight, heavy gauge ground wire leading down to a buried water pipe. It is not sufficient to disconnect the antenna from the receiver during thunderstorms.

Other pitfalls are less dangerous and relate to the receiver's performance. A common mistake when building a crystal radio is to load the tuned circuit excessively. The Q of the tuned circuit must remain high to give selectivity or strong radio stations will all mix together. A good design will usually have low-impedance taps on the inductor for connections to the antenna and diode as shown in the schematic. A long wire antenna with a good ground connection will connect to the lowest impedance tap whereas a shorter antenna with no ground connection may connect to a higher tap. The diode may be experimentally moved to different taps and even across the whole coil for maximum sensitivity. The antenna and diode connection may be made with alligator clips for easy experimentation.

Another potential problem area is the earphone. Not all crystal earphones are sensitive and the experimenter should test a few to get a "good" one. High impedance dynamic earphones are a bit more reliable and can give excellent results. Try an old telephone receiver or a modern portable tape player headset (some are high-Z and fairly sensitive). Low impedance earphones like those used with many portable radios will not work at all. A simple test is to hold one earphone wire between the fingers while scraping the other lead across a large metal object like a file cabinet. If static is heard in the earphone it will probably work well with the crystal radio.

The variable capacitor is often connected incorrectly. Make sure to connect the rotor to ground and the stator to the "hot" side of the coil. Otherwise, the radio will detune when the capacitor knob is touched. If detuning is noticed then try reversing the connections.

Some experimenters are tempted to omit the 82k resistor which discharges the capacitor on the theory that it wastes precious signal power. With a typical germanium diode, this little "improvement" may work somewhat but only because the diode has significant leakage and the performance will not be predictable. A dynamic earphone may be DC coupled eliminating the need for the resistor.

The coil may be wound on a 1.5 inch PVC pipe coupler as shown in the drawing. These typically have an outer diameter of about 2.2". Drill two small holes at each end to secure the ends of the coil. The wire type is not particularly critical but select a gauge and insulation so that the 65 turns cover about 2/3 of the coupler. An excellent choice is 30 AWG "wrap" wire from Radio Shack. The prototype uses this solid conductor wire with blue insulation. This wirewrap wire is available in 50' lengths on little spools and about 37' will be needed. A "loopstick" coil may be used in place of the coil shown. These coils have an adjustable ferrite core for tuning so a fixed value capacitor may be used in place of the variable capacitor shown. The coil, capacitor and a terminal strip for the other parts may be mounted to a small wooden board. (See photo of receiver with transistor amplifier below.)

If a metal chassis is used then the coil must be mounted horizontally and above the metal to prevent unacceptable loading.

Here are some alternative construction ideas:

Fahnestock clips make excellent connectors for the antenna and ground wires. The coil may be mounted above the board or chassis with angle brackets by adding another bend, as shown below. The windings may be quickly secured with a single layer of colored "Duck" tape that is now available in more attractive colors than gray or black. The taps to the coil can be located at the rear, near the bottom so that the unavoidable bulges in the tape don't show. An ordinary piece of wood may be quickly finished by applying adhesive-backed PVC film intended for kitchen cabinets. Just stick it on and trim flush with scissors.

One Transistor Amplifier/Detector

An amplifier may be added to boost the audio level as shown below. The current consumption of this amplifier is quite low and a power switch is not included. Disconnect the battery when the receiver is stored for long periods.

ï¿½ 1995, Charles Wenzel

Note: You may use the transistor above as a sensitive detector eliminating the need for the 1N34A diode. Simply leave out the diode, the 0.001 uF, and the 82k resistor. Connect the negative side of the 1 uF directly to the coil. Change the base resistor from 10 meg. to 1 meg. and change the collector resistor from 100k to 10k. Now add a 0.01 uF from the collector to the emitter and the modifications are complete. This detector is quite sensitive and will be overloaded by very long antennas! Use a shorter antenna or a coil tap very near ground if significant distortion is noticed. The circuit draws about 1/2 mA.

Crystal Radio Audio Amplifier

Here is a simple audio amplifier using a TL431 shunt regulator. The amplifier will provide room-filling volume from an ordinary crystal radio outfitted with a long-wire antenna and good ground. The circuitry is similar in complexity to a simple one-transistor radio but the performance is far superior. The TL431 is available in a TO-92 package and it looks like an ordinary transistor so your hobbyist friends will be impressed by the volume you are getting with only one transistor! The amplifier may be used for other projects, too. Higher impedance headphones and speakers may also be used. An earphone from an old telephone will give ear-splitting volume and great sensitivity! The 68 ohm resistor may be increased to several hundred ohms when using high impedance earphones to save battery power.

To use the circuit as a general-purpose amplifier, apply the input signal to the top of the potentiometer. (Leave out the diode and .002 uF capacitor.) A higher value potentiometer may be used for a higher input impedance.

ï¿½ 1995, Charles Wenzel

Information Log A06- Solar Flux

Solar Flux

One of the key solar indices is a measure known as solar flux. It’s used as the basic indicator of solar activity, and to determine the level or amount of radiation being received from the Sun.

The higher the solar flux, the better for amateur radio.

Solar Flux is measured in solar flux units (SFU) and is the amount of radio noise or flux that is emitted at a frequency of 2800 MHz. The solar flux is closely related to the amount of ionization and hence the electron concentration in the F2 region. As a result, it gives a very good indication of conditions for long-distance communication.

The figure for the solar flux can vary from as low as 50 or so to as high as 300. Low values indicate that the maximum useable frequency will be low and overall HF conditions will not be very good. Conversely, high values generally indicate there is sufficient ionization to support long-distance communication at higher-than-normal frequencies.

Typically values in excess of 200 will be measured during the peak of a sunspot cycle with high values of up to 300 being experienced for shorter periods.

Apart from the Solar Flux, another important influence on the ionosphere, and hence radio propagation prediction, is the level of geomagnetic activity. While the geomagnetic activity is a measure of the state of the Earth’s magnetic field, this, in turn, is influenced by the Sun. To indicate the state of Geomagnetic activity, there are two indices that are used that are related to each other.

The K Index and the A index.

Although different, both these indices give indications of the severity of magnetic fluctuations, and hence the level of disturbance to the ionosphere.

The K index is a three hourly measurement of the variation of the Earth’s magnetic field compared to what are “quiet day” conditions. The measurement is made using a magnetometer. This indicates the variation of the magnetic flux in nanoTeslas. This reading is then converted to the K index. The relationship is quasi-logarithmic, that is, an almost directly proportional on a logarithmic scale.

The A index is a linear measure of the Earth’s field. As a result of this, its values extend over a much wider range. It is derived from the K index by scaling it to give a linear value which is termed the “a” index. This is then averaged over the period of a day to give the A index. Like the K index, values are averaged around the globe to give the planetary Ap index.

Values for the A index range up to 100 during a storm and may rise as far as 400 in a severe geomagnetic storm.

Ap and Kp Indecies

There are two solar indices that are used to determine the level of geomagnetic activity… the A index and the K index.

These indices give indications of the severity of the magnetic fluctuations and hence the disturbance to the ionosphere. The first of the two indices used to measure geomagnetic activity is the K index.

The K-index quantifies disturbances in the horizontal component of earth’s magnetic field with an integer in the range 0–9 with 1 being calm and 5 or more indicating a geomagnetic storm.

The K index is a “quasi logarithmic” number and as such cannot be averaged to give a longer-term view of the state of the Earth’s magnetic field, so the A index was created which is a daily average.

During very severe geomagnetic storms the A index can reach values of up to 200 and very occasionally more.

The A index reading varies from one observatory to the next since magnetic disturbances can be local. To overcome this, the indices are averaged from Northern and Southern Hemisphere monitoring stations to provide the Ap index or the planetary value.

Similarly, the Kp index is the planetary average of all the K indices at observatories around the globe.

K values between 0 and 1 represent quiet magnetic conditions and this would indicate good HF band conditions, subject to a sufficient level of solar flux.

Values between 2 and 4 indicate unsettled or even active magnetic conditions and are likely to be reflected in the degradation of HF conditions. Moving up the scale, 5 represents a minor storm. A K value of 6 represents a larger storm and 7 through 9 represents a very major storm that would result in a radio blackout of HF communications.

Relationship between Kp index and A Index

Ap IndexKp IndexDescription

Quiet

Unsettled

Active

Minor storm

Major storm

132

Severe storm

208

Very major storm

400

Very major storm

Generally, the higher the flux, the better the conditions will be for the higher HF frequencies and even 6 meters. However, the levels need to be maintained for some days. In this way, the overall level of ionization in the F2 layer will build up. Typically values of 150 and more will ensure good HF band conditions, although levels of 200 and more will ensure they are at their peak.
The level of geomagnetic activity has an adverse effect, lowering the maximum usable frequencies. The higher the level of activity as reflected in higher Ap and Kp indices, the greater the depression of the MUFs. The actual amount of depression will depend not only on the severity of the storm but also its duration.
For Best Conditions, The Solar Flux Should Remain Above About 150 For A Few Days With The K Index Below 2.
When these conditions have been met, check out the bands and expect some good DX to be about!
For the latest solar indices, visit Solar Ham. This is not the only sight for current information, but it’s an easy to follow site which has current the latest images of the sun as well as graphs and predictions. You can also check out spaceweather.com which is another reputable site. And don’t forget closer to home, the Australian Bureau of Meteorology has a Space Weather Service. Finally, for more information about the Ionosphere, you’ll find details on the Sporadic E page.

Information Log A07: Noise Floor

What is Noise Floor for radio receivers
The noise floor of a radio receiver is the level of background noise that is present before any wanted signals are received.
Radio Receiver Sensitivity Includes:
Receiver sensitivity basics Signal to noise ratio SINAD Noise Figure, NF Noise floor Reciprocal mixing
The noise floor of a receiver is an important aspect of its operation as it gives a guide to the level of the minimum signal that can be received.
Noise is always present and received on a radio even when no wanted signals are present. The level of the noise floor determines the lowest strength signals that can be received and therefore the noise floor level is an important characteristic of any radio.
The noise floor can be defined as the measure of the signal created from the sum of all the noise sources and unwanted signals within a system.
Residual noise forms the noise floor
When designing a radio receiver for any radio communications system it is necessary to ensure that the performance of the radio receiver matches the performance required. For some radio communications systems, typically those operating on frequencies below about 30 MHz, the level of noise from the antenna system may be relatively high. In these cases, it is of no use to have an ultra-low noise radio receiver. However in applications such as VHF and UHF fixed or mobile radio communications systems where the levels of received noise are much lower, then a low noise radio receiver is more useful.
Radio receiver blocks that affect noise floor
In order to reduce the levels of noise and thereby improve the sensitivity of the radio receiver, the main element of the receiver that requires its performance to be optimised is the RF amplifier.
The use of a low noise amplifier at the front end of the receiver will ensure that its performance will be maximised. Whether for use at microwaves or lower frequencies, this RF amplifier is the chief element in determining the performance of the whole receiver. The next most important element is the first mixer.
Radio receiver noise floor
While noise can emanate from many sources, when looking purely at the receiver, the noise is dependent upon a number of elements. The first is the minimum equivalent input noise for the receiver. This can be calculated from the following formula:
P=k T BP=k T B
Where:
P is the power in watts
K is Boltzmann's constant (1.38 x 10^-23 J/K)
B is the bandwidth in Hertz
Using this formula it is possible to determine that the minimum equivalent input noise for a receiver at room temperature (290°K) is -174 dBm / Hz.
It is then possible to calculate the noise floor for the receiver at 20°C / 290°K in a 1Hz bandwidth:
Noise floor=−174 +NF+10log10(Bandwidth)Noise floor=-174 +NF+10log10(Bandwidth
Where:
NF is the noise figure
dBm is the power level expressed in decibels relative to one milliwat
The concept of noise floor is valuable in many radio communications systems and enables the radio receiver design and performance to be matched to the requirements of the overall system.

Information Log A08-Spectrum Analyzer

spectrum analyzer is a device used to measure the strength of an RF signal over a defined band of frequencies. The signal passes through a filter that allows only a specific range of frequencies, and the resulting signal is then passed through an amplifier and displayed on a screen.
The amplitude of the signal (the vertical axis on the screen) is then measured, and the plotted results represent the function of frequency (the horizontal axis). The overall shape of the resulting plot is the signal's spectral density.
Another primary function of a spectrum analyzer is to measure the power of known and unknown signals. Understanding how frequency, amplitude, and modulation parameters behave over short and long periods is critical to understanding the behavior of modern RF systems.
The MXA signal analyzer offers a robust performance in virtual identification of any wireless device signals with evolving testing demands including contemporary parametric or RF functional tests. – Source: Keysight
This article will look at the different types of spectrum analyzers, how they work, and their uses. This information will help you understand how to reliably detect and characterize RF signals that change over time.
What Are Spectrum Analyzers Used For?
By sweeping through the frequency spectrum, a spectrum analyzer provides a detailed analysis of the power of a signal at each frequency level. This information identifies which frequencies are responsible for the overall strength of the signal and troubleshoots any issue that causes a drop in signal strength. In addition, spectrum analyzers monitor a system's health by tracking changes in the strength of various signals over time.
The Keysight E4440A spectrum analyzer has been assisting the aerospace/aviation/defense and communications organizations in applications where the utmost performance and wideband analysis capacity are required – Source: Keysight
A spectrum analyzer is a powerful tool used in
Telecommunications to measure the performance of cellular networks and debug wireless communications.
The defense industry to test radar systems and detect hostile emitters.
Satellite communications to evaluate link quality and monitor interference.
Broadcasting to ensure compliance with regulations and optimize transmitter performance.
The aerospace industry to test aircraft avionics and ground-based radar systems.
Medical research to study brain waves and investigate the effects of electromagnetic radiation.
For engineers learning about spectrum analyzers, another piece of test equipment often used in conjunction with them is an oscilloscope. Using a spectrum analyzer and an oscilloscope together provides a complete picture of a signal.
Spectrum analyzers measure the amplitude of a signal as a function of frequency. They characterize signals spread out over a wide range of frequencies, such as those generated by RF transmitters. On the other hand, oscilloscopes measure a signal's voltage as a time (time domain). They are often used to troubleshoot electrical circuits by observing the waveforms of the various signals passing through them over short and long intervals.
For example, if you are trying to optimize an RF transmitter, you may use an analyzer to measure the output power as a function of frequency. Then you can use an oscilloscope to measure the shape of the transmitter's output waveform. By looking at both the power spectral density and the walveform, you can better understand how the transmitter is performing and identify any areas that need improvement.
These analyzers are also excellent at detecting and measuring noise and spurious signals. Signal noise is any unwanted signal that is present in a system. Spurious signals are not supposed to be present in a system. Together, these two types of interference can diminish and distort a signal.
By analyzing the frequency spectrum of a signal, a spectrum analyzer produces a graph that shows the signal's amplitude versus frequency. The amplitude measurement is in decibels, and the frequency is in hertz. By comparing these two measurements, you can identify any out-of-band signals or noise that may be present. This allows you to isolate and remove noise and spurious signals, ensuring accurate measurements.
How Do Different Types of Spectrum Analyzers Work?
There are two types of analyzers – analog and digital. An analog spectrum analyzer uses various techniques, such as filters and tuned circuits, to measure the strength and frequency of a signal. Digital analyzers use Fast Fourier Transform (FFT) to analyze the signal. FFT is a mathematical algorithm that converts the signal from the time domain to the frequency domain. This function allows the digital spectrum analyzer to take measurements very quickly.
Let's look at some different subtypes of spectrum analyzers and their uses.
Vector Spectrum Analyzer
A vector spectrum analyzer measures the spectral characteristics of a signal. They measure the amplitude and phase of a signal at each frequency within its operating range.
These measurements then generate a plot of the signal's amplitude as a function of frequency. This plot can provide valuable information about the spectral characteristics of the signal, which can optimize its transmission over long distances. The spectrum is simply a representation of energy across different frequencies.
The heterodyne principle is a crucial concept in signal processing and communications. In its simplest form, it states that you can combine two signals close in frequency to produce a new signal at the difference of their frequencies. This new signal, known as the beat frequency, contains information about both original signals.
Vector spectrum analyzers make use of the heterodyne principle to analyze signals. By mixing the target signal with a known reference signal, the VSA can create a beat frequency that has characteristics of the original signal. The VSA can then analyze this beat frequency to determine the signal's amplitude, phase, and other properties. This aspect makes VSAs an essential tool for measuring and troubleshooting complex signals.
Simplified flow diagram of a vector spectrum analyzer – Source: Keysight
VSA Pros VSA Cons
Measure the magnitude and phase of a signal. This is important because many real-world signals are not sinusoidal and have different amplitudes at varying frequencies.
Limited frequency range. They can only measure signals at a specific frequency.
Characterize complex signals. A complex signal can be a combination of multiple sinusoidal signals with different amplitudes, phases, and frequencies.
Limited dynamic range. They can only accurately measure signals within a certain range of amplitudes. Combined with their restricted frequency range, this may be limiting for some applications.
The ability to generate eye diagrams. These are graphical representations of how well an electrical signal conforms to certain standards. Eye diagrams are commonly used in digital communications systems to assess signal quality.
Typically have a much higher learning curve than their traditional counterparts. New users may find it challenging to become proficient in their use.
Swept Spectrum Analyzer
Swept spectrum analyzers sweep a sinusoidal signal across an RF (radio frequency) spectrum and measure the system's response under test at each frequency. It does this with the use of a local oscillator. The local oscillator's output signal mixes with the analyzer's input signal, and the resulting signal passes through a filter.
The amplified, filtered signal then travels to a detector which graphically shows the amplitude of the input signal as a function of frequency. The graph typically displays the results using a logarithmic scale for the amplitude (y-axis) versus a linear scale for the frequency (x-axis).
By observing the shape of the response curve, you can determine the system's center frequency, bandwidth, gain, and noise floor.
Swept spectrum analyzers troubleshoot and monitor RF systems, such as cellular communications, WiFi networks, satellite systems, and radar systems. They also measure the performance of RF components, such as filters, amplifiers, and antennas.
Simplified flow diagram of a swept spectrum analyzer – Source: Keysight
Swept Spectrum Analyzer Pros Swept Spectrum Analyzer Cons
Faster and easier to use. They take measurements in just a few seconds, while traditional spectrum analyzers can take several minutes.
Generally less sensitive than Fourier transform-based analyzers, making them less suitable for low-noise applications.
More accurate. Swept spectrum analyzers combine multiple measurements taken at different frequencies to create a more precise picture of the signal's power. Traditional spectrum analyzers measure the power of a signal at each frequency within its bandwidth. The strength of a signal can vary significantly from one frequency to another, resulting in an inaccurate measurement.
Subject to distortion due to how the signal spreads out over the frequency spectrum.
Less expensive. As they use fewer components than a traditional analyzer, a swept spectrum analyzer is an excellent choice if you need an affordable analyzer that is accurate and easy to use.
Requires a stable local oscillator. This can be challenging to generate for some frequencies.
FFT Spectrum Analyzer
A Fast Fourier Transform (FFT) spectrum analyzer measures the strength of signals at different frequencies. A mathematical operation splits the signal into multiple frequency bins (a range of frequencies used to group similar signals for further processing), and the spectrum analyzer displays the amplitude of each bin. The analyzer's resolution comprises the number of points used to sample the signal and the number of bins used to represent the signal.
The FFT Spectrum Analyzer also examines the spectra of signals that are time-varying or non-periodic. It is also helpful for analyzing modulated signals by a carrier wave. The FFT Spectrum Analyzer also measures the power spectral density and identifies harmonics in a signal.
Various applications use FFT spectrum analyzers, including
Telecommunications
Acoustics and audio signals
Radar
Power quality monitoring
Simplified flow diagram of a fast Fourier transform spectrum analyzer – Source: Keysight
FFT Spectrum Analyzer Pros FFT Spectrum Analyzer Cons
Highly detailed measurements. FFT spectrum analyzers can provide more detailed information about the frequency components of a signal. This allows for a more accurate analysis of the signal.
Limited signal types. FFT spectrum analyzers only analyze periodic signals. This means they are not well suited for analyzing transient signals, such as those found in pulsed radar or communication systems.
Faster measurements. FFT spectrum analyzers are typically quicker than other spectrum analyzers, making them more efficient.
Spectral leakage. When performing FFT-based analysis, windowing artifacts can be a significant problem, especially when using short windows. If you apply a window to a signal, it creates discontinuities that break the periodicity.
Accuracy. FFT spectrum analyzers are less affected by noise than other types of spectrum analyzers. This makes them ideal in environments with a lot of signal noise.
Causes aliasing. Windowing can also cause aliasing, which occurs when high-frequency components read as low-frequency spectral components, leading to errors in the measurement. To overcome this, an anti-aliasing filter removes high-frequency components from the signal.
Real-Time Spectrum Analyzer
Real-time Spectrum Analyzers (RSA) measure a signal's strength and frequency domain.As its name suggests, time-domain signals depend on time, whereas frequency-domain signals rely on frequency. RSAs use Fast Fourier Transform (FFT) to enable signal transformation from one domain to another, connecting the two. The time and frequency domains are effective analytical techniques that offer crucial information about signal properties.
RSAs provide a closer analysis of signal behavior by performing a "gapless" capture of the signal waveform, allowing you to see the signal's behavior over time in a single view. An RSA captures individual energy pulses with a time gate that opens and closes around each trigger event. The window size (gate) covers the expected pulse width plus a small margin to ensure the leading and trailing edges of the signal are both captured.
The trigger level detects signal energy above the noise floor, so blank sweep measurements (no signal triggers) are minimal. However, if the time between pulses is very short, gaps occur between capture sweeps.
Setting a low trigger level ensures that even weak signals will trigger a capture, while a short window width eliminates any delay in opening the gate when a pulse occurs. As a result, gapless capture provides a more accurate domain analysis of pulsed signals.
The RSA displays the domain information on a graph, which will help identify any problems with the signal. For example, too much noise or distortion will appear on the graph. Real-time analysis is mainly used in research and development settings as it is essential for characterizing signals and testing new equipment.
Real-Time Spectrum Analyzer Pros Real-Time Spectrum Analyzer Cons
Provides a more accurate picture of the signal environment. RSAs do not rely on taking samples of the signal at discrete points in time. Instead, they analyze the signal continuously, providing a “true” representation of the signal's behavior.
Often have reduced frequency resolution. This makes it difficult to identify subtle signal abnormalities.
Faster measurement setups and easier identification of signal anomalies.
Typically require more time to set up and configure than conventional models.
Easily configured to display only the information that is important to you. They offer great flexibility and insight into your signal environment.
Real-time analysis is less suited for analyzing very low-frequency signals.
How To Use a Spectrum Analyzer
The controls and interface of a spectrum analyzer can vary depending on the model and manufacturer, but most spectrum analyzers have several standard features.
You control the frequency span, range, and resolution by dials or buttons on the front panel. Adjusting these settings alters the range of frequencies displayed on the screen.
The trace, or line, on the screen represents the strength of the signal frequency. You adjust the amplitude of the trace by using the vertical scale knob. Move the trace up and down on the screen by adjusting the offset.
The level setting controls the maximum and minimum power levels displayed on the screen, known as the vertical scale. It is important to note that the level setting does not affect the actual power of the measured signal. You adjust the level setting by using the dial on the front panel.
The time base, or sweep speed, is another important spectrum analyzer feature. This controls how long it takes for the trace to move across the screen. A faster sweep speed will allow you to see brief signal anomalies. Adjust the time base to suit your desired speed by using a dial on the analyzer's front panel. Most spectrum analyzers have an auto-scale feature that automatically adjusts the level and sweep speed settings. This is a convenient feature if you are unsure what settings to use.

Information Log A09- The Radio Spectrum

Radio spectrum is the part of the electromagnetic spectrum ranging from 1 Hz to 3000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, have become widely used in modern technology, particularly in telecommunication.

Information Log A10- Numbers Stations

http://www.numbersoddities.nl

numbers station is a shortwave radio stationcharacterized by broadcasts of formatted numbers, which are believed to be addressed to intelligence officers operating in foreign countries.[1] Most identified stations use speech synthesis to vocalize numbers, although digital modes such as phase-shift keying and frequency-shift keying, as well as Morse code transmissions, are not uncommon. Most stations have set time schedules, or schedule patterns; however, some appear to have no discernible pattern and broadcast at random times. Stations may have set frequencies in the high-frequency band.[2]

Numbers stations have been reported since at least the start of World War I and continue to be in-use today. Amongst amateur radio enthusiasts there is an interest in monitoring and classifying numbers stations with many being given nicknames to represent their quirks or origins.

According to the notes of The Conet Project,[3][4] which has compiled recordings of these transmissions, numbers stations have been reported since World War I with the numbers transmitted in Morse code. It is reported that Archduke Anton of Austria in his youth during World War I used to listen in to their transmissions, writing them down and passing them on to the Austrian military intelligence.[5]

Numbers stations were most abundant during the Cold War era. According to an internal Cold War-era report of the Polish Ministry of the Interior, numbers stations DCF37 (3.370 MHz) and DFD21 (4.010 MHz) transmitted from West Germany beginning in the early 1950s.[6]

Many stations from this era continue to broadcast and some long-time stations may have been taken over by different operators.[7][8] The Czech Ministry of the Interior and the Swedish Security Service have both acknowledged the use of numbers stations by Czechoslovakia for espionage,[9][10][11] with declassified documents proving the same. Few QSL responses have been received from numbers stations[12] by shortwave listeners [13] who sent reception reports to stations that identified themselves or to entities the listeners believed responsible for the broadcasts, which is the expected behaviour of a non-clandestine station.[14][15]

One well-known numbers station was the E03 "Lincolnshire Poacher",[16] which is thought to have been run by the British Secret Intelligence Service.[17] It was first broadcast from Bletchley Park in the mid-1970s but later was broadcast from RAF Akrotiri in Cyprus. It ceased broadcasting in 2008.[18] In 2001, the United States tried the Cuban Five on the charge of spying for Cuba. The group had received and decoded messages that had been broadcast from the "Atención" number station in Cuba.[19]

Atención spy case[edit]

The "Atención" station of Cuba became the world's first numbers station to be officially and publicly accused of transmitting to spies. It was the centerpiece of a United States federal court espionage trial, following the arrest of the Wasp Network of Cuban spies in 1998. The U.S. prosecutors claimed the accused were writing down number codes received from Atención, using Sony hand-held shortwave receivers, and typing the numbers into laptop computers to decode spying instructions. The FBI testified that they had entered a spy's apartment in 1995, and copied the computer decryption program for the Atención numbers code. They used it to decode Atención spy messages, which the prosecutors unveiled in court.[19]

The United States government's evidence included the following three examples of decoded Atención messages.[19]

"prioritize and continue to strengthen friendship with Joe and Dennis"
"Under no circumstances should [agents] German nor Castor fly with BTTR or another organization on days 24, 25, 26 and 27." (BTTR is the anti-Castro airborne group Brothers to the Rescue)
"Congratulate all the female comrades for International Day of the Woman."

The moderator of an e-mail list for global numbers station hobbyists claimed that "Someone on the Spooks list had already cracked the code for a repeated transmission [from Havana to Miami] if it was received garbled." Such code-breaking may be possible if a one-time pad decoding key is used more than once.[19] If used properly, however, the code cannot be broken.

Recent cases[edit]

In 2001, Ana Belén Montes, a senior US Defense Intelligence Agency analyst, was arrested and charged with espionage. The federal prosecutors alleged that Montes was able to communicate with the Cuban Intelligence Directorate through encoded messages, with instructions being received through "encrypted shortwave transmissions from Cuba".

In 2006, Carlos Alvarez and his wife, Elsa, were arrested and charged with espionage. The U.S. District Court for the Southern District of Florida[20][which?] stated that "defendants would receive assignments via shortwave radio transmissions".[citation needed]

In June 2009, the United States similarly charged Walter Kendall Myers with conspiracy to spy for Cuba, and receiving and decoding messages broadcast from a numbers station operated by the Cuban Intelligence Directorate to further that conspiracy.[21][22] As discovered by the FBI up to 2010, one way that Russian agents of the Illegals Program were receiving instructions was via coded messages on shortwave radio.[18] It has been reported that the United States has used numbers stations to communicate encoded information to persons in other countries.[19] There are also claims that State Department-operated stations, such as KKN50 and KKN44, used to broadcast similar "numbers" messages or related traffic, although these radio stations have been off the air for many years.[23][24]

North Korea revived number broadcasts in July 2016 after a hiatus of sixteen years, a move which some analysts speculated was psychological war;[25] sixteen such broadcasts occurred in 2017, including unusually timed transmissions in April.[26]

Suspected use for espionage[edit]

It has long been speculated, and was argued in one court case, that these stations operate as a simple and fool-proof method for government agencies to communicate with spies working undercover.[27] According to this hypothesis, the messages must have been encrypted with a one-time pad to avoid any risk of decryption by the enemy. Writing in 2008, Wallace & Melton described how numbers stations could be used in this way for espionage:[28]

The one-way voice link (OWVL) described a covert communications system that transmitted messages to an agent's unmodified shortwave radio using the high-frequency shortwave bands between 3 and 30 MHzat a predetermined time, date, and frequency contained in their communications plan.[28]

The transmissions were contained in a series of repeated random number sequences and could only be deciphered using the agent's one-time pad. If proper tradecraft was practised and instructions were precisely followed, an OWVL transmission was considered unbreakable. As long as the agent's cover could justify possessing a shortwave radio and he was not under technical surveillance, high-frequency OWVL was a secure and preferred system for the CIA during the Cold War.[28]

Evidence to support this theory includes the fact that numbers stations have changed details of their broadcasts or produced special, nonscheduled broadcasts coincident with extraordinary political events, such as the attempted coup of August 1991 in the Soviet Union.[29]

A 1998 article in The Daily Telegraph quoted a spokesperson for the Department of Trade and Industry (the government department that, at that time, regulated radio broadcasting in the United Kingdom) as saying

"These [numbers stations] are what you suppose they are. People shouldn't be mystified by them. They are not for, shall we say, public consumption."[30]

Generally, numbers stations follow a basic format, although there are many differences in details between stations. Transmissions usually begin on the hour or half-hour.[citation needed]

The prelude, introduction, or call-up of a transmission (from which stations' informal nicknames are often derived) includes some kind of identifier,[31] for the station itself, the intended recipient, or both. This can take the form of numeric or radio-alphabet "code names" (e.g. "Charlie India Oscar", "250 250 250", "Six-Niner-Zero-Oblique-Five-Four"), characteristic phrases (e.g. "¡Atención!", "Achtung!", "Ready? Ready?", "1234567890"), and sometimes musical or electronic sounds (e.g. "The Lincolnshire Poacher", "Magnetic Fields"). Sometimes, as in the case of radio-alphabet stations, the prelude can also signify the nature or priority of the message to follow (e.g., it may indicate that no message follows). Often the prelude repeats for a period before the body of the message begins.[citation needed]

After the prelude, there is usually an announcement of the number of number-groups in the message,[31] the page to be used from the one-time pad, or other pertinent information. The groups are then recited. Groups are usually either four or five digits or radio-alphabet letters. The groups are typically repeated, either by reading each group twice or by repeating the entire message as a whole.[citation needed]

Some stations send more than one message during a transmission. In this case, some or all of the above process is repeated, with different contents.[citation needed]

Finally, after all the messages have been sent, the station will sign off in some characteristic fashion. Usually, it will simply be some form of the word "end" in whatever language the station uses (e.g., "End of message; End of transmission", "Ende", "Fini", "Final", "конец"). Some stations, especially those thought to originate from the former Soviet Union, end with a series of zeros, e.g., "00000" "000 000"; others end with music or other sounds.[31]

Because of the secretive nature of the messages, the cryptographic function employed by particular stations is not publicly known, except in one (or possibly two[32]) cases. It is assumed that most stations use a one-time pad that would make the contents of these number groups indistinguishable from randomly generated numbers or digits. In one confirmed case, West Germany did use a one-time pad for numbers transmissions.[33]

Transmission technology[edit]

High-frequency radio signals transmitted at relatively low power can travel around the world under ideal propagation conditions – which are affected by local RF noise levels, weather, season, and sunspots – and can then be best received with a properly tuned antenna (of adequate, possibly conspicuous size) and a good receiver.[19]

Although few numbers stations have been tracked down by location, the technology used to transmit the numbers has historically been clear—stock shortwave transmitters using powers from 10 kW to 100 kW.[citation needed]

Amplitude modulated (AM) transmitters with optionally–variable frequency, using class-C power output stages with plate modulation, are the workhorses of international shortwave broadcasting, including numbers stations.[citation needed]

Application of spectrum analysis to numbers station signals has revealed the presence of data bursts, radioteletype-modulated subcarriers, phase-shifted carriers, and other unusual transmitter modulations like polytones.[34] (RTTY-modulated subcarriers were also present on some U.S. commercial radio transmissions during the Cold War.[35])

The frequently reported use of high-tech modulations like data bursts, in combination or in sequence with spoken numbers, suggests varying transmissions for differing intelligence operations.[36]

The Speech/Morse generator (pictured here) is a machine that has been used for many well-known numbers stations

Those receiving the signals often have to work only with available hand-held receivers, sometimes under difficult local conditions, and in all reception conditions (such as sunspot cycles and seasonal static).[19] However, in the field low-tech spoken number transmissions continue to have advantages even in the 21st century. High-tech data-receiving equipment can be difficult to obtain and even a non-standard civilian shortwave radio can be difficult to obtain in a totalitarian state.[37] Being caught with just a shortwave radio has a degree of plausible deniability, for example, that no spying is being conducted.[citation needed]

Interference[edit]

Interfering with other broadcasts[edit]

The North Korean foreign language service Voice of Korea began to broadcast on the E03 Lincolnshire Poacher's former frequency, 11545 kHz, in 2006, possibly to deliberately interfere with its propagation.[citation needed] However, Lincolnshire Poacher broadcasts on three different frequencies, and the remaining two have not been interfered with. The apparent target zone for the Lincolnshire Poacher signals originating in Cyprus was the Middle East, not the Far East, which is covered by its sister station, E03a Cherry Ripe.[38][39]

On 27 September 2006, amateur radio transmissions in the 30 m band were affected by an S06 "Russian Man"[40] numbers station at 17:40 UTC.[39]

In October 1990, it was reported that a numbers station had been interfering with communications on 6577 kHz, a frequency used by air traffic in the Caribbean. The interference was such that on at least one monitored transmission, it blocked the channel entirely and forced the air traffic controller to switch the pilot to an alternative frequency.[39]

A BBC frequency, 7325 kHz, has also been used. This prompted a letter to the BBC from a listener in Andorra. She wrote to the World Service Waveguide programme in 1983 complaining that her listening had been spoiled by a female voice reading out numbers in English and asked the announcer what this interference was. The BBC presenter laughed at the suggestion of spy activity. He had consulted the experts at Bush House (BBC World Service headquarters), who declared that the voice was reading out nothing more sinister than snowfall figures for the ski slopes near the listener's home. After more research into this case, shortwave enthusiasts are fairly certain that this was a numbers station being broadcast on a random frequency.[41]

The Cuban numbers station "HM01" has been known to interfere with shortwave broadcaster Voice of Welt on 11530 kHz.[42]

Attempted jamming[edit]

Numbers station transmissions have often been the target of intentional jamming attempts. Despite this targeting, many numbers stations continue to broadcast unhindered. Historical examples of jamming include the E10 (a station thought to originate from Israel's Mossad intelligence agency) being jammed by the "Chinese Music Station" (thought to originate from the People's Republic of China and usually used to jam "Sound of Hope" radio broadcasts which are anti-CCP in nature).[43]

Identification and classification[edit]

Monitoring and chronicling transmissions from numbers stations has been a hobby for shortwave and ham radio enthusiasts from as early as the 1970s.[44] Numbers stations are often given nicknames by enthusiasts, often reflecting some distinctive element of the station such as the interval signal. For example, the "Lincolnshire Poacher" station played the first two bars of the folk song "The Lincolnshire Poacher" before each string of numbers.[45] Sometimes these traits have helped to uncover the broadcast location of a station. The "Atención" station was thought to be from Cuba, because a supposed error allowed Radio Havana Cubato be carried on the frequency.[46][full citation needed]

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Although many numbers stations have nicknames which usually describe some aspect of the station itself, these nicknames have sometimes led to confusion among listeners, particularly when discussing stations with similar traits. M. Gauffman of the ENIGMA numbers stations monitoring group originally assigned a code to each known station.[47]

Portions of the original ENIGMA group moved on to other interests in 2000 and the classification of numbers stations was continued by the follow-on group ENIGMA 2000.[48] The document containing the description of each station and its code designation was called the "ENIGMA Control List" until 2016, after which it was incorporated into the "ENIGMA 2000 Active Station List"; the latest edition of the list was published in September 2017.[49] This classification scheme takes the form of a letter followed by a number (or, in the case of some "X" stations, more numbers).[50] The letter indicates the language used by the station in question:

E indicates a station broadcasting in English.
G indicates a station broadcasting in German.
S indicates a station broadcasting in a Slavic language.
V indicates all other languages.
M is a station broadcasting in Morse code.
X indicates all other transmissions, such as polytones, in addition to some unexplained broadcasts which may not actually be numbers stations.

There are also a few other stations[31] with a specific classification:

SK: Digital mode
HM: Hybrid mode
DP: Digital-pseudo polytone

Some stations have also been stripped of their designation when they were discovered not to be a numbers station. This was the case for E22, which was discovered in 2005 to be test transmissions for All India Radio.[51]

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