Satellites for SWLs!
Satellites need not be only something for amateurs to enjoy. Anyone who possesses a decent receiver can have their slice of the action. This page is dedicated to the SWLs out there who want to hear (or see!) signals from the sky.
Amateur voice satellites can be divided broadly into two groups. Firstly, there are the traditional "linear transponder" satellites. These satellites receive a specific range of frequencies (typically 40 - 100 kHz) in one band, convert them to another band using a mixing process similar to that used in a superheterodyne receiver and amplify the converted signal for transmission back to Earth. Linear transponders are capable of relaying several different signals simultaneously. More recently, some satellites have been carrying crossband FM repeaters instead of linear transponders. These repeaters are similar to their familiar terrestrial cousins in that they receive an FM signal on a specific channel, demodulate the signal and retransmit the signal on a new frequency. Unlike linear transponders, but like conventional FM repeaters, these satellites can only carry one QSO at a time. Most amateur voice satellites use linear transponders (there are two known orbiting FM repeaters accessible in VK at the time of writing).
To successfully receive an amateur satellite, you need a receiver capable of receiving the frequency and mode of the satellite's transmissions and a suitable antenna system. Most SWLs will have a scanner, capable of receiving FM on the VHF and UHF bands, a shortwave receiver that goes to at least 30 MHz, or both. The better equipped SWLs may have multimode capabilities in the VHF/UHF spectrum, though this isn't very common for SWLs.
For antennas, an existing HF dipole and VHF/UHF omnidirectional antennas will work in a pinch. The typical VHF/UHF collinears (e.g. amateur or UHF CB verticals) typically have a low angle of radiation, and better results may be obtained with a simple ľ wave groundplane, or for the more serious, a turnstile antenna. Discones can work reasonably well too, especially on 2 metres (145 MHz). Some satellites can also be received on a handheld scanner. The more adventurous may want to build small handheld Yagis for 145 and 435 MHz to improve reception in these bands. Finally, though not essential, it is very strongly recommended to have a computer, satellite tracking software and an Internet connection available. The Internet connection is for downloading the latest Keplerian elements for the tracking software (and the software itself if you donít have any), as well as checking satellite home pages for transponder schedules and other information. Besides, the Internet is fun when the birds arenít overhead!
Hearing your first satellite! This isnít anywhere near as daunting as it sounds. The first thing is to have a look around your shack and see what equipment you have. If, like many SWLs, you have AM/FM/FM wide only scanners on VHF/UHF, then you are limited to the FM satellites on these bands. Those with shortwave receivers can also have a listen for linear transponders with a downlink in the 10 metre (29 MHz) band. For further introductory information on satellites (generally aimed at amateur readers, but useful for SWLs), check out "Working Your First Satellite" and "Working the Easy Sats Down Under". In addition, there are several excellent introductory articles on AMSAT's web site.
Time for a bit of an inventory. As I said before, most SWLs will have VHF FM receivers (scanners), HF SSB receivers or both. If you have VHF gear, your best bet is to listen for the FM satellites, namely SO-35, UO-14 and FO-29's digitalker when it's active. Those with HF receivers will be best advised to try and receive RS-13. Those with very good gear could also try RS-15, though this bird isn't the easiest to receive. If you're a CB operator, it could be well worth trying to hook up your 27 MHz antenna (especially if it's a beam) to your shortwave receiver.
One other thing that needs mentioning is Doppler shift. Doppler shift is a phenomenon that all of us will recognise in a different situation. Imagine you're waiting at a railway crossing. A train passes at high speed, blowing its horn. As the train passes you, the pitch of the horn appears lower than when it was approaching. That apparent shift in frequency is Doppler shifting caused by the relative speed of the train to you shortening, then later lengthening the wavelength of the sound as seen by the observer. On board the train, the pitch of the horn does not alter, but the pitch of the bells at the crossing does. When a satellite passes overhead, the transmitted and received signals are affected in a similar way. With the satellite passing at 27,000 km/h or more, a signal at 436 MHz can be shifted by up to 10 kHz from its actual transmitted frequency. Some satellites are designed with this in mind, and have AFC (Automatic Frequency Control) circuits to partially compensate for Doppler shift. Doppler shift is only significant for FM satellites on 70cm or higher bands. On 2m, the 3 kHz Doppler shift can usually be accommodated by an ordinary FM receiver, provided it's on the correct frequency. 29 MHz Doppler shift is much smaller, around +/- 600 Hz, but the satellites with downlinks in this region carry SSB signals, which are far more sensitive to Doppler shift and require constant tuning to correctly resolve.
Now it's time to choose a 'bird' to monitor. I'll cover VHF satellites first, then the HF ones. On VHF/UHF, there are 3 satellites which can be received over Australia (Northern Hemisphere readers have another one called AO-27 which we don't have here). Two of these satellites, namely UO-14 and FO-29 have downlinks in the 70cm band, and the other, SO-35 (otherwise known as SUNSAT), has a 2m downlink.
SO-35 is the easiest of the FM voice satellites to receive. It has a very strong downlink which is (nominally) on 145.825 MHz (measured around 1.7 kHz lower at the time of writing) which can be easily received on a handheld scanner if you replace the standard rubber ducky with a better handheld antenna. Receiving SO-35 is very easy, requiring only a little bit of effort and a quick surf of the Internet to obtain details of up and coming voice passes. No Doppler correction is normally required, though I do find the downlink seems to be a bit below its nominal frequency, and tuning down 5 kHz towards the end of the pass can improve the recovered audio.
During your preparation, log onto the Internet and check the SUNSAT page at http://sunsat.ee.sun.ac.za/index.html (click on the Amateur Radio link for the skeds), to find out when the transponder is scheduled to be active over Australia and the frequencies that will be used (usually 145.825 MHz). Alternative, Australian readers may prefer to use my SO-35 page, which avoids the need to run any tracking software at all! I have a series of pre-calculated passes for major centres in Australia, New Zealand, Papua New Guinea and Fiji, which can be accessed here. The times given on both pages are in UTC. My SO-35 page will tell you exactly when SO-35 is visible, as well as the exact times that the transponder is in FM mode. If you have tracking software, download the latest Keps while youíre online and run a simulation of the pass. The software will allow you to know where the satellite will be at any given point in time, the maximum elevation of the pass and the exact times it will be visible, and often, the amount of Doppler shift that will be present. While tracking SO-35 is not critical for your success, it is good practice for the other birds.
Unlike SO-35, UO-14 takes a little more effort to receive. The downlink is much weaker, due to lower transponder power, as well as an increase of 9dB of free space loss due to the higher frequency. However, on the plus side, UO-14, unlike SO-35, operates continuously as an FM repeater. Listeners using high gain verticals such as amateur or UHF CB base antennas are likely to be disappointed. A handheld with a good UHF antenna will receive UO-14 reasonably well. Those who are handy with a soldering iron or metalwork may want to build a small handheld beam for 435 MHz, which will make a huge improvement in received signal strength. In general, it is easier and cheaper to use portable gear than fixed gear for UO-14. Fixed stations may want to try an omnidirectional satellite antenna such as a turnstile or eggbeater (have a look at amateur antenna books for construction details of these sorts of antennas). Fixed stations will also benefit from installing a preamp at the antenna to boost the received signal before it enters the coax. If you use a preamp, make sure it is at the antenna, as close as possible, and not at the receiver end of the feedline, otherwise you will not gain any real benefit.
Once you have a setup capable of receiving UO-14, it's time to get right into it! Firstly, you will need to know when UO-14 is available. I do keep a listing of passes for Melbourne, Australia, but I strongly recommend you run your own tracking software so you can be sure where the satellite is yourself. Some tracking software can also tell you how much Doppler shift there will be on the downlink. Speaking of Doppler shift, unlike SO-35, you will need to correct for Doppler when listening to UO-14. The nominal downlink frequency for UO-14 is 435.070 MHz, but for a high elevation pass, you should start listening on 435.080 MHz. As the satellite moves towards you, then away, you will need to tune down in 5 kHz or smaller steps. By the time the pass finishes, you will be receiving on 435.060 MHz. Passes that are low on the horizon may need only +/- 5 kHz Doppler correction, instead of the +/- 10 kHz described above.
One thing about UO-14 is that it is easy to know when you are hearing the downlink. The background noise with the mute open drops slightly and becomes less "harsh", even when there's no uplink signal.
FO-29 in Digitalker mode.
FO-29 is normally configured as a store and forward packet system or a linear transponder (which requires SSB gear to receive). However, it is occasionally configured as a "digitalker". When the digitalker is active, FO-29 acts as a beacon which replays a pre-recorded message in a continuous loop. The beacon (downlink) frequency is 435.910 Mhz, and again, allow up to +/- 10 kHz for Doppler, as with UO-14. The signal strength of the beacon should be similar to UO-14, and the comments about antenna and receiving systems for UO-14 apply here as well.
Now, we come to the HF satellite, RS-13. Unlike the satellites mentioned above, RS-13 uses a linear transponder, which is capable of relaying multiple QSOs simultaneously. Instead of FM, CW (Morse Code) and SSB are usually used on this type of satellite. FM is seldom, if ever used, due to its inefficient use of transponder power or bandwidth. However, RTTY (radio teletype), SSTV (slow scan television) and other narrowband specialised modes may be received from time to time.
RS-13's downlink is not am single signal, but instead a band of signals. There is a beacon on 29.458 MHz, and the transponder "passband" extends from 29.460 MHz to 29.500 Mhz. Signals from amateurs may be received anywhere within this bandwidth. Normally, CW will be used on the lower part and SSB higher up. While Doppler shift at this lower frequency is only +/- 600 - 700 Hz, the use of SSB and CW makes Doppler compensation much more critical, and you will need to adjust for Doppler almost continuously during the whole pass to keep the received audio intelligible. Similarly, you will likely have to retune your receiver as each participant in the conversation takes turns, as they're likely to appear to be on different frequencies as observed from your location.
RS-13 usually requires no specialised antennas for casual listening. An existing HF dipole, long wire or CB vertical can be pressed into service with good results. I can hear the beacon on a Dragon 10m handheld with the 60cm long flexible whip! Experimenters may want to try building a 10m turnstile or horizontal loop, which may yield better signals under some circumstances. A 27 or 28 MHz beam is also likely to help on low elevation passes, if you have one.
When monitoring RS-13, it is best to start by listening to the beacon frequency (or slightly above, to allow for Doppler), as the beacon is usually clearly audible, and over the Australia/New Zealand region, RS-13 can be pretty quiet. The beacon consists of Morse Code at a fairly high speed (25 WPM or more), and is usually clearly distinguishable from any other signals that may be present. Doppler shift should be evident within 30 seconds from when you first hear the beacon. Once the beacon becomes fairly strong, you may like to try tuning up through the passband and see if there are any stations. Because there is no set "carrier" frequency", it is best to tune up and down the passband, as though you were looking for new shortwave stations. Hopefully you will soon encounter a QSO and be able to listen in. Remember that the different stations involved may seem to be on quite different frequencies. This is normal, unless everyone is running a computer controlled station or is very close together.
Sometimes, the downlink from RS-13 may be distorted. Morse can sound "hissy", without a "note", and SSB may become rather strange sounding, especially if the satellite is near one of the Earth's poles. This is not due to some fault, but is more likely caused by auroral activity near the poles. Believe me, it sounds quite wierd the first time you hear it, and it's a good excuse to learn Morse Code, as that's all that gets the message through sometimes!
Where to from here?
Once you've mastered the simple birds, you may want to try something more challenging. There are linear transponders in the 2m and 70cm amateur bands, which require a bit more attention to Doppler tuning. Also, you will probably need to buy or build a receive converter so that you can use your shortwave receiver to resolve the CW and SSB signals from these satellites. Alternatively, you may like to try something different and "download" weather pictures from weather satellites on 137 MHz, receive amateur operations from Mir and the up and coming International Space Station, or monitor commercial and military satellite communications. Even digital communications can be found on Amateur satellites, if this catches your fancy. More information of these sorts of activities can be found in SWL magazines or on the World Wide Web. Of course, you may decide you want to join in the action yourself and get your own Amateur licence, so you can work the birds yourself.
Listeners need not miss out on all of the excitement, and with relatively simple gear, anyone with commonly available receiving equipment can see for themselves the excitement of satellite operation. With a bit of luck and some preparation, listeners can monitor cosmonauts on Mir or future astronauts on the International Space Station. Satellite monitoring is within the reach of any SWL or scanner operator, and many enjoyable hours can be had listening to what's happening over your head.
And in case you have got the satellite bug, here's a few more satellites you can monitor with varying degrees of difficulty (some may require receive converters).
|Satellite Frequency Chart||RS-12||RS-13|
|15m Uplink (Modes K&T)||21.210 - 21.250 MHz||21.260 - 21.300 MHz|
|2m Uplink (Mode A)||145.910 - 145.950 MHz||145.960 - 146.000 MHz|
|10m Downlink (Modes K&A)||29.410 - 29.450 MHz||29.460 - 29.500 MHz|
|2m Downlink (Mode T)||145.910 - 145.950 MHz||145.860 - 145.900 MHz|
|10m Beacons||29.408 & 29.454 MHz||29.458 & 29.504 MHz|
|2m Beacons||145.912 & 145.958 MHz||145.862 & 145.908 MHz|
|ROBOT Uplinks||21.129 & 145.831 MHz||21.139 & 145.840 MHz|
This page is written as an introduction to operating the Radio Sputnik 12 and
13 amateur satellites. It is designed to give the beginner a clear understanding
of what is required to operate it, as well as inform the experienced satellite
operator of the differences from standard VHF/UHF satellites. If you have
already read this page or are simply looking to ask some questions or set up a
scheduled contact, you may:
CLICK HERE FOR THE RS-12/13 FORUM
To operate in "Mode A" you would require a 2 meter SSB or CW transmitter and a 10 meter receiver. For "Mode K" you would need either two radios with two antennas or one radio with the capability to switch between two different frequencies on two seperate bands. Those bands being 15 meter transmit and 10 meter receive. The more rare "Mode T" requires a 15 meter transmitter and a 2 meter capable receiver. Sometimes the modes and thusly the frequencies are combined; those being "Mode KT" and "Mode KA". (It is important to note that in the US, Technician and above licensees can utilize Mode A, but to use Mode K or Mode T, an Advanced or Extra class license is required.)
Many hams work the RS-12/13 satellites with little more than a dipole or
vertical antenna. In fact, I have had many QSOs with 5 watts and a vertical, but
it does take a little practice. On Mode A, 25-50 watts is usually sufficient
into an omnidirectional antenna. A dipole will work just fine for reception, but
many have found a full wave horizontal loop to be the best. A beam is a plus,
but it also requires learning how to turn the rotor in QSO. No
"special" equipment is required other than a computer to figure the
satellite's "track" or 'when the satellite will be in range'. Running
the "keplerian elements" or the numbers to calculate position is the
same as for any other satellite. Or you can get them e-mailed to you from the
NASA website. They have a service called J-Pass. Just click on the link below to
go there and sign up. You will need to know your latitude and longitude, (which
can be obtained from Buckmaster's
or QRZ callsign servers) if your city or
one close to you is not listed. Also you will have to enter your time zone and
some e-mail preferences. You will need to choose the RS-12/13 satellite and any
others you may wish to track. Then J-Pass will send you e-mail updates of the
satellite's passes over your location.
CLICK HERE TO REGISTER WITH J-PASS E-MAIL SERVICE
Which leads us to awards. The reason for exchanging grid squares is that many stations are competing for awards for a certain number of grid squares, usually 100 or more for VUCC (VHF UHF Century Club). Its very similar to DXCC when chasing DX. Others may be trying for Worked All States, or any one of many specialized satellite awards offered by various AMSAT clubs. But many just enjoy the thrill of working another station through a man-made object, completely independent of propagation! However, sometimes propagation does come into play since these satellites utilize HF frequencies! More on this exciting facet later...
One note on QSLing. When sending a QSL for a satellite QSO, it is considered a courtesy to write in your grid square, if it is not already printed. And to state the satellite name and mode of operation. For instance, on my cards I write in 21/29 under MHz signifying Mode K, or I could just write in "Mode K". And under Mode, I write CW/RS-13 or whatever is appropriate.
Doppler Shift happens to radio waves just as it does to a train whistle or a siren as they pass by. It causes the frequency to rise and fall. With the satellite, it just seems like the other guy has an older radio with a real bad drifting problem! But seriously, as a signal goes up to the satellite it is affected and again as it is retransmitted back down it is affected, so it is not as simple as the siren or train whistle analogy. Suffice it to say that frequencies tend to drift as the satellite passes over, and stations constantly have to adjust frequency. But which frequency do you adjust?!! Back to that in a bit.
Okay, it's time for the satellite to come over the horizon. You will begin to hear a very weak CW signal that gets gradually louder. Now not real loud. Even if it were overhead it may not get more than S7 or so, depending on your receiver setup. If you have a high noise level at your location, you may not be able to hear the satellite at all, but lets say you can. Now tune up the band a bit. In the lower half of the passband 29.460-475 you will generally find the CW signals; in the upper half 29.475-29.500, the voice. You will notice that no one is any stronger than the beacon. To understand why, lets take a look at how the "transponder" or satellite repeater works.
A transponder has a "passband" or a frequency section on its receiver that it will hear signals from the ground. It then takes ALL those signals and 'translates' them to a transmitter frequency section in a 'proportionate' amount. This means that if one signal is louder in the receiver, it will be louder coming out of the transmitter. You see, the satellite transmitter is only 8 watts and all the signals coming back down have to SHARE that 8 watts of power. It is common courtesy to turn your own transmit power down so that you are no stronger than the beacon, or else you will use more than your fair share of the signal. You will be really strong and no one else will be heard. When a strong DX station comes on frequency, they sometimes come through the satellite, unknowingly of course, and cause all the other signals to "take a fade" as it is called.
OK, so now you hear a fellow calling CQ RS CQ RS on about 29.465. "What do I do?" you ask. Well, here's a rule of thumb for these particular satellites or "birds" as we like to call them. The last two digits will be pretty close to the same. Meaning, try tuning up on 21.265 or 145.965 (listen first so you don't interfere with a "terrestrial" or non-satellite QSO). See if you can hear your own signal, by sending a series of dits. If you can hear your own signal, then he should be able to as well. If you are using just one radio and switching bands, just try winging it. Maybe try just a little higher in frequency (21.265.4 or 145.965.4) to offset the Doppler shift and give him a call. When he comes back to you, (notice I said when not if!) you will be copying what he is sending and he will start drifting. That means that when he turns it over to you, you have drifted as well! How do we compensate for that?!! Well, the standard practice with satellites is that we always adjust the higher frequency. If you transmit on 15 and listen on 10, you adjust your receive so that you can keep hearing him. (You don't want to change transmit frequencies as you may drift into an ongoing terrestrial QSO!) If you are running 2 up and 10 down, you would adjust your transmitter frequency, WHILE TRANSMITTING, so that you continue to hear yourself in your receiver.
I know it sounds complicated, but you get the hang of it pretty quick. If you listen to other QSOs in progress, you'll hear some of the stations constantly adjusting frequency. And you may think, "But they aren't even on the same frequency as each other," but that is how it sounds to YOU. They have adjusted their radios to hear each other just fine. It's that the Doppler is different for you at your location... Don't worry you'll get it.
After you make contact, he will call you and send his info. Then you do likewise. Send him an RST (never 599, be honest) your state and your name and then a break, like so: AA0PW de AC5DK GM TU UR RST 559 559 ARK ARK OP KEVIN KEVIN HW? BK. Then he will probably say 73 and thanks and sign off. You will do the same and THAT'S IT! You did it! Your first Satellite QSO. Now that wasn't really so hard was it?
Something else of interest is the effect of propagation on satellite signals. Sometimes in the spring when the MUF gets high and the "skip" starts coming in on 2 meters, you may notice that SOME of the signals on the satellite sound all warbly and funny, almost like the effect the Aurora Borealis has. It is caused by the 2 meter signals bouncing around through the ionosphere.
On 10 and 15 meters the propagation has an even greater effect. Sometimes, stations on the other side of the world may be "skipping" around the ionosphere and "bouncing" into the satellite, and their signals can be heard in the downlink, even though when you turn on 15 meters, you don't hear a thing. In fact, it is possible to have a QSO through the satellite when it is BELOW the horizon of one or both of the stations. This is called "Over the Horizon" technique (or OTH for short). Some stations have used this method to achieve DXCC through the RS-12 satellite, but that's a little complicated for right now. Suffice it to say, it can be done.
There is also something called the ROBOT. It is a computer circuit that can copy your CW signal, (with limitations), and respond to you with your callsign and a QSO number. You can even send for a QSL card for such contacts. I have never been able to make one of these QSOs myself, but I know that it can be done. Perhaps in the future I can add another page with more detailed information about this and OTH technique for the experienced operator.