[NOTE: this originated as a Linux User Net discussion topic for Aug. 5, 2019]
The term “SDR” — Software Defined Radio — has been widely used and misused, both for descriptive and marketing purposes. As a result, it has can mean many things, depending on the context in which it is used, as well as the perspecive of the speaker.
If someone tells you, “I have an SDR”, you have to dig deeper to discover what that “SDR” actually is. Part of the confusion comes from the fact that “software-defined radio” originally described a process, not an object.
I have come up with a list of seven possibile meanings — there may be more.
People sometimes cofuse Digital Signal Processing with SDR. The difference is that DSP works on audio signals, not radio signals. Many analog radios use DSP in their audio stages. Note that a true SDR almost always will encorporate DSP. So, this is not actually SDR.
Again, not really SDR. I hear this most often applied to QRP rigs, such as the uBitx. The radio itself is fully analog, but it is controlled by a digital device, such as an Arduino or similar microcontroller board. This is nothing new, of course — virtually every ham rig produced in recent years has come with a digital interface. What is new is that the control device is open to be programmed by the user. I believe this is the source of confusion with SDR.
Here the radio is fully software-defined in the inside, but externally appears to be, and functions as, a traditional radio. These rigs are essentially designed to be drop-in replacements for older analog units, sporting the cutomary knob and button controls, along with legacy interfaces such as serial ports. It looks and feels so much like an analog radio that you wouldn’t know it’s digital inside without being told. Examples: Icom IC-7300, Yaesu FTDX-101D.
This is an all-in-one rig that includes a full MS Windows PC internally. That gives it the capability of running various ham software inside the box, rather than in a connected PC. Hook up monitor, keyboard, and mouse, and you have a complete shack-in-a-box. Example: Expert Electronics MB1.
I’m always on the lookout for new examples of redundant acronyms, where people pronounce the acronym as a word and follow it with the word that the final letter of the acronym stands for. Examples are “PIN number” and “ATM machine”. I recently added “NIC card” to my list (thanks to KA7PLE).
“SDR radio” might be one — or it might not. It can be argued that if “SDR” describes the process of manipulating RF signals with software and the word “radio” describes an object that functions within the accepted meaning of “a radio”, then “radio” has two different meanings – and so there is no redundancy, even though it sounds that way.
Source Credit: KC7MM Wiki
C4FM stands for Continuous 4-level Frequency Modulation. (FM), and is the actual digital modulation of the radio signal used in System Fusion over VHF/UHF. Wires-X is the node linking/voip technology that allows nodes to link across the Internet.
For WIRES-X, an amateur node station connecting to the Internet is used as the access point and connects the wireless communication to the Internet. Users’ stations can communicate with other amateur stations all over the world using a node within the radio wave range.
WIRES-X supports the C4FM digital and the clear and crisp voice technology enables high sound quality. By repeating C4FM digital data as it is via the Internet, users can enjoy clear voice communications even if they are thousands of miles away each other.
Utilizing the digital communication, the WIRES-X operation is simple, easy and user friendly.
Varieties of the new functions as well as voice communications expands opportunities for enjoyment of ham station operation.
WIRES-X automatically connects to nodes and rooms via the Internet. No more need to verify connection IDs or transmit cumbersome DTMF connection codes.
Information about nodes and rooms is exchanged via C4FM Digital signaling. Thanks to automatic reconnection to the previous contact, all you need to do is press PTT and start talking.
Easily search for new nodes and rooms, and initiate communication promptly when you find an ID that captures your interest.
Yaesu FT-70D, finding and saving Wires X rooms into memory
A repeater, in concept, is not really a complicated device. A repeater is an automatically controlled transmitter and receiver that simply transmits what the receiver hears simultaneously. Imagine having a receiver on one channel, and a high power transmitter on the other, and then holding the microphone of the transmitter in front of the speaker of the receiver. Now make the operation fully automatic. Any user that can be heard by the receiver has the effectiveness of the high power transmitter at his control.
In general, repeater systems are usually located in places of high elevation (on tall towers, on top of mountains or tall buildings) and are equipped with large and efficient antennas, extremely low loss feedlines, and a transmitter and receiver that is very durable, rated for continuous duty, and built to be as immune as possible to interference.
The end result? People using a repeater get much greater range from their radio equipment than would be possible talking from radio to radio. This is how an individual with a portable walkie-talkie (handheld) transceiver can communicate with people many miles away with good clarity.
Repeaters are used in police, fire and ambulance service communications (commonly called “Public Safety”), Commercial (Business) Communications, Federal, State and Local Government agencies, Emergency Communications, and by Amateur Radio Operators. Repeaters can be powered by the regular commercial power lines, or they can be connected to multiple sources of power, including batteries and/or generators for when commercial power is lost. Repeaters can be built that are extremely power efficient and may run exclusively from batteries; recharged by solar, wind or water power.
Here’s a link to a solar-powered amateur repeater: http://www.polkcounty.org/ham/
What is Simplex
Simplex is point to point communications without the use of a repeater. Simplex operation utilizes the same frequency for receive and transmit, like a CB radio. I.E. Portable to Portable or Mobile to Mobile. The commercial 2-way world calls Simplex operation ‘Talk Around” because you are talking around the repeater, not through it.
There are such things as Simplex Repeaters. These machines listen on the frequency for activity, when it recognizes something it will begin to record that activity for a pre-determined time; usually 1 minute. A slang term for these is a “parrot repeater”. After the activity ceases or the time has expired, the unit will repeat what it has recorded. This method of communications is somewhat cumbersome over a conventional repeater; because you are forced to listen to what you said earlier in time and the channel usage is problematic as you never know when someone else is recording; however it should not be discounted as these types of systems can be very beneficial.
What is Duplex
The simple explanation of full duplex operation is like the telephone, where both people can talk at the same time. In contrast, a pair of handhelds operate in half-duplex mode because only one person can talk at a time. Since the ‘repeater’ listens and talks at the same time in relaying your message, it operates in full duplex mode.
How does a Repeater work
At first glance, a repeater might appear complicated, but if we take it apart, piece by piece, it’s really not really so difficult to understand. A basic repeater consists of several individual pieces that, when connected, form a functional system. Here’s a simple block diagram of a repeater:
The collection of the antenna, the feedline, the duplexer, and the interconnecting cables is frequently called the “antenna system”.
Most repeaters use only one antenna. The antenna simultaneously serves both the transmit and receive RF (Radio Frequency) signals that are going in to and out of the repeater. It’s generally a high performance, durable, and very efficient antenna located as high on a tower or structure as we can get it. Antenna systems of this type can easily cost $500 or more, and that’s not including the feedline. On the other hand, when properly installed and maintaned they can last from 10 to 25 years.
The feedline on most repeaters isn’t just a piece of standard coax cable, it’s what’s called Hardline. This stuff is more like a pipe with a center conductor than a cable. It’s hard to work with and very expensive. So why do we use it? Performance! The signal loss is much lower in hardline than in standard cable, so more power gets from the antenna to the receiver and weaker signals can be received. A hard rule is that once any percentage of a received signal is lost that you can’t get it back – ever.
Remember, the signal at a repeater site doesn’t just travel a few feet to an antenna like in a mobile rig. It may go hundreds of feet up the tower to the antenna. Just for fun check out the specs on a roll of coax some time and see how many dB of loss you’ll get from 200 feet of cable, and remember 3 dB is 1/2 of your power, and 10 dB is 90% of your power. Hardline also tends to be more durable than standard cable, which increases reliability and helps us minimize the financial expense, and the tower climbs to replace it.
This device serves a critical role in a repeater. To make a long story short, the duplexer separates and isolates the incoming signal from the outgoing and vice versa. Even though the repeaters input and output frequencies are different, the duplexer is still needed. Why? Have you ever been in a place where there’s lots of RF activity, and noticed the receive performance of your handheld radio degrades to some degree? This is called desensitization, or desense, and it’s a bad thing on a repeater. The receiver gets noisy or gets desensitized to the point of total deafness from the strong RF signals being radiated in its vicinity and confused about which signal it should receive.
The result is poor receive quality, or in extreme cases, complete lack of receive capability. Keep in mind that in this example, the radios are picking up radiated power from one another and that’s enough to cause trouble. Now imagine how much trouble there will be if you not only have the transmitter and receiver close together, but connect them to the same antenna!
Transmitting only a few hundred kHz away in frequency would blow away the input to the receiver if the equipment was simply connected together with a Tee. That’s where the duplexer comes in; it prevents the receiver and transmitter from ‘hearing’ one another by the isolation it provides. And the more isolation the better.
A duplexer is a device that is referred to by several different names like cavities or cans. A duplexer has the shape of tall canisters and is designed to pass a very, very narrow range of frequencies and to reject all others. There is some loss to the system because of the duplexer (called the “insertion loss”), however, the advantage of being able to use a single antenna and a single feedline usually outweighs the drawbacks.
Receives the incoming signal. This receiver is generally a very sensitive and selective high performance one which helps weaker stations to be heard better by the repeater. It’s also where CTCSS (Continuous Tone Coded Squelch System) or “PL” decoding takes place. More on this later.
Most machines have a transmitter composed of two parts: an ‘exciter’ and a power amplifier. The exciter created low level RF energy on the proper frequency and then modulates it with the audio. The power amplifier stages simply boosts the level so the signal will travel further. Transmitters come in two types: intermittent duty and continuous duty. One that is rated for continuous duty is preferred.
The term “Station” is used to describe a stationary two way radio set; which includes the transmitter, receiver and sometimes the control circuitry. One example is the dispatch radio for a fire department. A ‘Repeater Station’ is a station designed to be used as a duplex repeater.
This is the brain of the repeater. It handles station identification (through either CW or voice), activates the transmitter at the appropriate times, controls the autopatch, and sometimes does many other things. Some machines also have a DVR (Digital Voice Recorder) for announcements and messages. The controller is a little computer that’s programmed and optimized to control a repeater.
The various models of controllers have different useful features like speed-dial for phone patches, a voice clock, facilities to control a remote base or linking, etc. The controller gives the repeater its ‘personality’. Whenever you’re using a repeater, you’re interacting with its controller. In the early days of repeaters the controller was a large chassis full of relays and timers. These days a controller is most often a microcomputer based unit.
What is a Phone Patch or Autopatch? AKA “The Patch”
Many repeaters have a feature that allows you to place a telephone call from your radio. Phone calls are generally restricted to the local calling area of the repeater to avoid long distance charges to the repeater’s sponsors. If in doubt, ask if the repeater has an open patch and how to access it.
When using the patch it is common courtesy to announce your intentions, e.g. “This is N3XZY on the patch”. This may help to prevent anyone from keying up while you are trying to use the function. In most areas when you are finished with the patch the accepted protocol is to announce it, e.g. “This is N3XZY clear the patch”.
A DVR is a Digital Voice Recorder, or in modern terms a “voice mail” system for the repeater. Usually it’s an option that is installed into the controller.
Operating using a repeater isn’t difficult. A good source of info is the ARRL Repeater Directory. It’s an inexpensive book with repeater listings all over the US. It contains frequency, offset and whether the repeater is + or – in shift (see “offset” below), whether or not it requires a PL tone, and other features (like an autopatch, or repeater-to-repeater linking).
What is Offset
In order to listen and transmit at the same time, repeaters use two different frequencies. On the 2 meter ham band these frequencies are 600 kHz apart. As a general rule in the USA, if the output frequency (transmit) of the repeater is below 147 MHz then the input frequency (listening) is 600 kHz lower. This is referred to as a negative offset. If the output is 147 MHz or above then the input is 600 kHz above. This is referred to as a positive offset. However in any given area the offset rules can be different.
Virtually all ham radios sold today set the offset once you have chosen the operating frequency. As an example one repeater output is 145.270 MHz. The input, or the frequency it listens on is 144.670 MHz (600 kHz below). If you have your radio tuned to 145.270 MHz with the offset enabled, when you push the PTT switch (Push-To-Talk) your radio automatically transmits on 144.670 MHz. When you release the PTT to listen, the radio reverts back to 145.270 MHz to listen on the repeater’s output frequency.
|Standard Repeater Input/Output Offsets|
|6 meters (50-54 MHz)||No real nationwide standard, it varies widely.|
Most common are -500 kHz, -600 kHz or -1.0 MHz
|2 meters (144-148 MHz)||Up and down 600 kHz, depends on frequency|
|1.25 meters (222-224 MHz, also called “220”)||Down 1.6 MHz|
|70 cm (440 MHz, also called “UHF”)||Up or down 5 MHz, depends on local area usage|
|33 cm (900 MHz)||-25 MHz|
|23 cm (1200 MHz)||-20 MHz|
Note: There are exceptions to the above so check local repeater listings.
Why do Repeaters use an Offset
To use a repeater a user station must use a different transmit frequency than receive frequency. This is a form of duplex, or two frequency operation. It is known as half-duplex as you do not receive and transmit at the same time but normally use the push-to-talk button on your microphone to switch between the two.
Most repeater installations use the same antenna for transmit and receive. Without having an offset the repeater would simply hear itself when it was transmitting on the same frequency it was listening on. Even with the offset, the two frequencies are close enough that antenna system isolation is required. Again, this isolation is afforded by the duplexer.
What is Carrier Access, Tone Squelch, CTCSS or a PL Tone
Carrier Access, or Carrier Squelch means that the repeater is looking for a carrier on the receiver frequency to open the squelch. A circuit called a Carrier Operated Switch (COS) or Carrier Operated Relay (COR) senses the squelch opening, and tells the repeater that there is a carrier on the input. The controller keys the transmitter, thereby repeating the signal.
Continuous Tone Coded Squelch System, or CTCSS, is a radio communications industry standard signaling scheme. It provides an electronic means of allowing a repeater to respond only to stations that encode or send a very precise audio tone at a very low level superimosed on the transmitter along with the microphone audio. The CTCSS system is used to prevent the repeater receiver from responding to unwanted signals or interference (it’s looking for both the carrier and the tone before the signal is considered as valid).
If a repeater is “in tone mode” that means it requires a CTCSS tone to activate the repeater. If it is in “Carrier mode” then it is ignoring the CTCSS decoder, if there is one. Modern repeater controllers offer a way to switch back and forth, even automatically, between the two modes. Originally there were 32 standard tones, now there are 37.
Some manufacturers offer more, but most repeaters use one of the original 32 so as to allow the older radios to use the system. Aftermarket tone generators from several differnet manufacturers allow any station to be set up to transmit a CTCSS tone. The tones are in the 67-250 Hz range and are called sub-audible, because they’re below the normal voice audio range of 300-3000 Hz. This doesn’t mean you can’t or won’t hear them; they can be quite noticeable depending on the radio you’re using.
PL, an acronym for Private Line, is Motorola’s proprietary name for CTCSS. General Electric uses the name “Channel Guard” or CG for the same system. Other names, such as Call Guard, Quiet Channel or Quiet Tone are used by other manufacturers.
In days of old, repeaters that used PL were considered to be closed or private. This is no longer the case as tone operation has become more the rule instead of the exception. Uninformed people use CTCSS to “solve” interference problems. It doesn’t. It just covers them up, or hides them. The unwanted signal is still on the repeater input, the tone decoder simply prevents the repeater from making it obvious.
Of course, everything these days is digital. A later system called Digital Coded Squelch (DCS) uses 85 different sub-audible digital bit streams. Motorola uses the name Digital Private Line, or DPL for this. Other manufacturers use different names. DPL is gaining in popularity since more radios now come with it as a standard feature.
How do you call someone on an Amateur Repeater?
First, listen to make sure that the repeater is not already in use. Then listen some more. If you are a new ham that has never used a repater before it might pay to listen for a week or so and see what goes on, who seems to be the “regular users”, and if you know any of them, perhaps from the local ham club meeting.
When you are satisfied that the repeater is not in use, begin with the callsign of the station you are trying to contact followed by your callsign. e.g. “W3ABC this is N3XYZ”. If you don’t establish contact with the station you are looking for, wait a minute or two and repeat your call.
If you are just announcing your presence on the repeater it is helpful to others that may be listening if you identify the repeater you are using. e.g. “This is N3XYZ listening on 6-2-5”. This allows people that are listening on radios that scan several repeaters to identify which repeater you are using (and therefore which microphone to pick up to answer you).
If the repeater you are using is a busy repeater you may consider moving to a simplex frequency (transmit and receive on the same frequency), once you have made contact with the station you were calling. Repeaters are designed to facilitate communications between stations that normally wouldn’t be able to communicate because of terrain or power limitations. If you can maintain your conversation without using the repeater, going “simplex” will leave the repeater free for other stations to use.
The first and most important rule is LISTEN FIRST. Few things are more annoying than someone that “keys up” in the middle of another conversation without first checking to make sure the repeater is free. Saying that your volume control was down too low and you didn’t hear any conversation is no excuse – it just says that you didn’t chack your own station before you used it. If the repeater is in use, wait for a pause in the conversation and simply announce your callsign and wait for one of the other stations to acknowledge your call.
When you are using the repeater leave a couple of seconds between exchanges to allow other stations to join in or make a quick call. Most repeaters have a “Courtesy Tone” that will help in determining how long to pause. The courtesy tone serves two purposes. Repeaters have a time out function that will shut down the transmitter if the repeater is held on for a preset length of time (normally three or four minutes). This ensures that if someone’s transmitter is stuck on for any reason, it won’t hold the repeater’s transmitter on indefinitely.
When a ham is talking and releases the push-to-talk switch on their radio, the controller in the repeater detects the loss of carrier and resets the time-out timer. Many of the modern computerized controllers allow the owner to program a “beep” to indicate that the timer is reset. This beep is called the courtesy beep, or the courtesy tone.
If you wait until you hear this beep (normally a couple of seconds) before you respond, you can be sure that you are pausing a suitable length of time. After you hear the beep, the repeater’s transmitter will stay on for a few more seconds before turning off. This is referred to as the “carrier delay”, or the “hang in timer”. The length of the delay will vary from repeater to repeater but the average is about 2 or 3 seconds. You don’t have to wait for the transmitter to drop off the air before keying up again, but you should make sure that you hear the courtesy tone before going ahead.
Note: If you don’t wait for the beep the time-out timer to may not reset. Some repeater clubs have a rule that if you time-out the repeater you get to buy a round of coffee at the next ham club meeting.
What is “Doubling” ?
When two stations try to talk at the same time the signals mix in the repeater’s receiver and results in a buzzing sound or squeal. When you are involved in a roundtable discussion with several other stations it is always best to pass off to a specific person rather than leave it up it the air. e.g. “W3ABC to take it, this is N3XYZ” or “Do you have any comments Fred?, this is N3XYZ”. Failing to do so is an invitation to chaos and confusion.
It is for this very reason that when groups hold scheduled Nets (network of hams meeting on air at a predetermined time), they assign a Net Control station. The Net Controls job is to make sure there is an orderly exchange and that all stations get a chance to speak. Listen to a local net and you will get an idea of the format and how the Net Control juggles the various stations and traffic.
It’s a job almost anyone can handle, but as you will discover, some are much better at it than others. And if you try your hand at being Net Control for a night, you will discover just how hard it can be! (and you will gain a lot of respect for those that have the knack to do it and make it sound easy). A well run net is both informative and entertaining!
What is a Control Operator?
The Part 97 of the FCC Rules requires all stations in the Amateur Service that are capable of operating unattended must be monitored for proper operation while in the unattended mode. This monitoring function is accomplished by a control operator. The Control Op can be the licensee of the station or anyone he or she chooses. In many cases, he or she also ends up being the person that answers questions about the repeater.
What is White Noise?
White noise is a term used to describe a spectrum of broad band noise generated in a receiver’s detector and sampled to control the receiver’s squelch. When you open the squelch control and hear the rushing noise from the speaker, this is white noise. When the receiver is in carrier squelch mode the squelch circuit uses the presence of that noise to decide that the signal has gone away and it should mute the receiver speaker.
When the receiver is in tone squelch mode it uses the abscence of the tone AND the presense of the noise to indicate loss of signal. The “squelch tail” is that burst of white noise that you hear that starts when someone unkeys and ends when the squelch circuit actually mutes the receiver audio (some people mistakenly use the term to refer to the carrier delay mentioned above).
I hope this article has explained the Repeater in enough detail that you understand what it is and how to use it. If there is any part of this article that seems vague or confusing, please write me and I’ll do my best to explain it better.
Email Kevin: kuggie //at// kuggie //dot// com
Credits: Repeater Builder
The word “grounding” — meaning a connection to the Earth — is casually applied to so many different purposes in Amateur Radio, it’s no wonder there are many opinions and misconceptions about it. “Bonding” is a less familiar term to most amateurs. In the electrical sense, bonding simply means “to connect together” so that voltage differences between pieces of equipment are minimized.
Why Are Grounding and Bonding Important?
There are three needs we are trying to satisfy:
• AC safety: protect against shock hazards from ac-powered equipment by providing a safe path for current when a fault occurs in wiring or insulation.
• Lightning protection: keep all equipment at the same voltage during transients and surges from lightning and dissipate the lightning’s charge in the Earth, routing it away from equipment.
• RF management: prevent unwanted RF currents and voltages from disrupting the normal functions of equipment (also known as RF interference or RFI).
Why Is “Grounding” So Complicated?
The very word — grounding — means a lot of different things depending on who you’re talking to and what you’re talking about. Isn’t grounding just connecting equipment to the Earth? That is certainly one definition of grounding.
The British use the terms “earthing” and “protective earth conductor” which are more exact references to what the connection is for. But the layer of soil and rock at the Earth’s surface is not a magic zero-voltage point into which we can pour any amount of electric charge where it safely disappears! The current’s strength and frequency, soil characteristics, whether it is wet or dry, the length of the path to the Earth connection and through the soil — all of these affect what our equipment experiences at the “ground” connection.
Station Grounding for Amateur Radio – Ask Dave
Grey or gray line propagation is a form of HF radio propagation apparent at dawn and dusk where signals traveling along the line are heard at much higher strengths.
Grey line or gray line propagation is a form of radio signal propagation that provides surprisingly long distance radio communications at dawn and dusk sometimes when other forms of ionospheric propagation may not be expected to provide signal paths of these distances.
Grey line propagation is only present around dawn and dusk and therefore it cannot be used to support global radio communications at any time. Accordingly it tends to be used chiefly by radio amateurs and a few other users who can accommodate the timing and other limitations of its availability.
For grey line propagation signals travel along the grey or twilight zone between night and day. This is area where night and day meet and it is also known as the terminator. In this region signals on some frequencies are attenuated much less than might normally be experienced and as a result signals can be received at surprisingly high levels over very long distances – even from the other side of the globe.
The improved propagation conditions around the grey line are most noticeable primarily on the lower frequency bands in the HF portion of the spectrum where the level of ionization in the D layer has a much greater effect on signals that on those frequencies higher up.
The diagram below shows how the illumination remains on the F region much longer than on the D region, and this creates a situation where the D region has faded away, but the F region remains intact.
In reality, the D region fades before dusk as the illumination from the sun reduces around dusk at the Earths surface. The level of ionization in the D region drops very quickly around dusk and after dark because the air density is high and recombination of the free electrons and positive ions occurs comparatively quickly.
This occurs while the level of ionization is still high within the F layer, which gives most of the radio propagation for long distance radio communications. This occurs because the F region is much higher in altitude, and as the Sun sets it remains illuminated by the Sun’s radiation for longer than the D region, which is lower down. Also recombination of the ions takes longer because the air is very much thinner at the altitude of the F region compared to that of the D region.
The same occurs in the morning as the Sun rises. The F region receives radiation from the Sun before the D region and its ionization level starts to rise before that of the D region. As the level of the D region ionization is low, this means that the degree of attenuation to which the lower frequency signals are subjected to is very much less than in the day. This also occurs at a time when the F region ionization is still very high, and good reflections are still achievable. Accordingly this results in much lower overall path losses around the grey line than are normally seen.
In terms of the diagram above, the altitude of the D and F regions have been highly exaggerated to show the mechanism behind the grey line. This means that the fading of the D region starts to occur well before dusk and the F region remains in place until after dusk – and grey line propagation occurs around the region of dusk and dawn.
In fact, when looking at the region of the radio terminator it should be remembered that there are a variety of variables that mean that it does not exactly follow the day time / night time terminator as seen on the Earth’s surface. The ionized regions are well above the Earth’s surface and are accordingly illuminated for longer, although against this the Sun is low in the sky and the level of ionization is low. Furthermore there is a finite time required for the level of ionization to rise and decay. As there are many variables associated with the “radio signal propagation” terminator, the ordinary terminator should only be taken as a rough guide for radio signal propagation conditions.
Although it may be obvious to mention, grey line propagation can only exist for stations at locations that fall along the grey line or terminator. This significantly limits the number of areas for a given station at a particular location to set up long distance communication, although there will be slight changes over the course of the year for many stations.
Frequencies that are affected by this form of propagation are generally limited to frequencies up to about 10 MHz. Frequencies higher in frequency than 10 MHz tend to be attenuated to only a minor degree by the D region and therefore there is little or no enhancement around dusk and dawn by this mechanism.
Grey line propagation is particularly noticeable on lower frequencies, for example the 3.5 MHz amateur radio band. Normally signals may be heard over distances of a few hundred kilometers in the day, and possibly up to or two thousand kilometers at night for those stations with good antennas.
Grey line propagation regularly enables long distance radio communication contacts to be made with stations the other side of the globe at very good strength levels.
The optimum times are normally around the spring and autumn equinoxes as neither end of the link is subject to the propagation extremes of summer and winter. It is at these times of year that long distance radio communication can be established with stations on the other side of the globe at remarkably good signal strength levels.
It is still possible for higher frequency signals to be affected by a grey line type enhancements. This occurs as a result of the fact that a propagation path is opening in one area and closing in another giving a short window during which the path is open on a particular frequency or band of frequencies.
Looking at the MUFs over the course of the day can demonstrate the way in which this occurs. The level of ionization in the F layer falls after dusk, and rises at dawn. This results in the MUF falling after dark.
Accordingly, stations experiencing dawn find the MUF rises and those experiencing dusk find it that it falls. For frequencies that are above the night time MUF, and for stations where one is experiencing dusk and the other dawn, there is only a limited time where the path will remain open. This results in a similar effect to that seen by the lower frequency grey-line enhancement.
The path of the grey line changes during the course of the year. As the angle subtended by the Sun’s rays changes with the seasons, so the line taken by the terminator changes. This results from the fact that during the winter months, the Northern Hemisphere of the earth is titled away from the Sun, and towards it during the summer months.
The converse is obviously true for the southern hemisphere. In addition to this the width of the grey line also changes. It is much wider towards the poles because the line between dark and light is less will defined as a result of the fact that the Sun never rises high in the sky at the poles. It is also much narrower at the equator. This results in grey line propagation being active for longer at the poles than at the equator.
Grey line propagation provides an opportunity for long distance radio communication contacts and links to be made, often with stations the other side of the globe. Signals travel along the grey line, or terminator and suffer comparatively little attenuation. An opening via grey line propagation may only last for half an hour, but it gives the opportunity for radio communication to be established between stations as far away as the other side of the globe.
Attention D1 Emergency Coordinators. If you would like to post any Public Service announcements or upcoming Events on the District 1 Website public service page, just send an email to Mark, KC7NYR and I will get your event posted or use the contact page with the request.
This service is open to all Counties in District 1 Counties; Clackamas, Clatsop, Columbia, Multnomah, Tillamook, Washington.
If you like me to also make announcements on the D1 Net about your upcoming Event, just let me know and I would be happy to do this on your behalf.
Public Service Page
To contact as many stations as possible on the 160, 80, 40, 20,15 and 10 Meter HF bands, as well as all bands 50 MHz and above, and to learn to operate in abnormal situations in less than optimal conditions.
Field Day is open to all amateurs in the areas covered by the ARRL/RAC Field Organizations and countries within IARU Region 2. DX stations residing in other regions may be contacted for credit, but are not eligible to submit entries.
Each claimed contact must include contemporaneous direct initiation by the operator on both sides of the contact. Initiation of a contact may be either locally or by remote.