Working the Easy Sats Down Under.
There are a number of excellent introductory articles on amateur satellite operation, some of which inspired me to move beyond SO-35 and try some other 'birds', such as UO-14, RS-13 or FO-20. However, operation from the Australia/NZ region is a little different to that in the Northern Hemisphere. The most notable differences are that AO-27 doesn't operate down here, and traffic on all satellites is much lighter than it is in the Northern Hemisphere, so operating procedures are sometimes different as a result.
What is an Easy Sat?
There is no "one" definition of an Easy Sat, but most people agree that an "Easy Sat" is one which requires little or no extra equipment than most amateurs would already have. I'll follow this basic definition, taking into account the antenna and power requirements as well as the actual transceivers used. While packet specialists may consider digital satellites "easy", I haven't included them, mainly because I haven't worked digital satellites.
Doppler and all that stuff ("Why is everyone drifting so badly?").
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. For SSB/CW operation, Doppler shift is significant on all satellites. The amount of Doppler shift for a low Earth orbiting satellite is proportional to frequency, and is approximately as follows:
15m +/- 400 Hz
10m +/- 600 Hz
2m +/- 3 kHz
70cm +/- 10 kHz
It is customary (unless running computer frequency control) to vary the higher frequency in use to compensate as best as possible for Doppler shift. For example, on Mode (2m up, 10m down), one would adjust the 2m uplink, but on Mode J (2m up, 70cm down), one would adjust the 70cm downlink to compensate for Doppler. More info on Doppler shift can be found here.
Inteoducing the Easy Sats!
There are several amateur satellites which could be classed as "Easy Sats". The easiest of the "Easy Sats" are literally orbiting FM repeaters. There are two FM satellites, which are accessible over the Southern Hemisphere. namely SO-35 and UO-14. The rest of the easy sats are linear transponders, which take a block of frequencies and convert them to a block of frequencies in another band using a mixing process much like a transverter or superheterodyne receiver in space. There are 3 linear transponders which I'd class as "easy", namely RS-13, FO-20 and FO-29 (in JA mode). FO-29 also has a "digitalker", which is an orbiting voice beacon which occasionally gets activated from time to time, and is very easy to hear in this mode. In the following table, I list the easy sats, in approximate order of increasing difficulty, and list the minimum and recommended equipment requirements to satisfactorily work each bird.
|Satellite||Minimum equipment required.||Recommended minimum equipment.|
|FO-29 in digitalker mode||Handheld scanner with rubber duck||Handheld 70cm transceiver with 1/2 wave antenna|
|SO-35 (parrot mode)||2m handheld with rubber duck||2m handheld with small Yagi|
|SO-35 (Mode B)||2m/70cm handheld with rubber duck||2m handheld with 5/8 wave, 70cm handheld with 1/2 wave.|
|UO-14||2m handheld with 5/8 wave, 70cm handheld with 1/2 wave.||2m and 70cm handhelds with small beams, or high power 2m into vertical, 70cm with small beam.|
|RS-13||2m handheld, 10m SSB with small vertical (if you can send CW with the PTT!), or 2 HF rigs and wire antennas.||2m and 10m all mode, or 2 HF transceivers, dipoles or turnstiles on HF, vertical or turnstile on 2m.|
|FO-20 and FO-29 in JA mode.||2m and 70cm all mode with portable beam.||2m and 70cm all mode with portable or rotatable beams.|
As you can see, the requirements for many satellites are quite modest, and you probably already have all the gear you need for some of them in the shack. Here's a run down in detail.
FO-29 in digitalker mode:
Being a beacon, FO-29's digitalker is continuously transmitting when the satellite is overhead. When it's operational, it uses most of the transmitter power, so it is a reasonably strong signal and can be received with simple handheld receivers. The frequency of the digitalker is 435.910 MHz, and the mode is FM. Because the transmission is on 70cm, keep in mind the 10 kHz Doppler shift, so you will need to listen 10 kHz higher than the nominal frequency and gradually adjust this down as the digitalker drifts down the band. By the end of the pass, you will be listening around 10 kHz below the nominal frequency. The hardest part about receiving the digitalker is knowing when it's active, as the satellite is more often in Mode JA (analogue transponder) or Mode JD (digital store and forward), both of which take a bit more work to access.
SO-35 in parrot mode:
SO-35 is a relatively new satellite, and also the subject of my article, "Working Your First Amateur Satellite!". SO-35 currently has two modes of operation, namely parrot mode and Mode B (can also use Mode J, but this isn't routinely used). Parrot mode is, as the name suggests, store and forward voice mode, where the satellite listens for signals on a particular frequency and retransmits them several seconds later. In the case of SO-35, the parrot repeater normally operates on 145.825 MHz, and runs in a continuous cycle as follows: SO-35 sends a single tone, after which there is 10 seconds for stations to transmit to the satellite. After the 10 seconds is up, the satellite transmits two tones, followed by the audio stored in the previous 10 seconds. This pattern repeats for the rest of the pass. Unlike most voice modes, the parrot repeater requires you to only have one transceiver, which can be a handheld. However, to ensure you get a good signal into the bird (you're transmitting "blind", as you can't hear your uplink), it is recommended to use 5 watts and a small Yagi, or a 25 watt base/mobile rig into a vertical as a minimum. I found the latter worked reasonably well. Parrot mode does require a higher level of operator skill. To find out more, have a look at Taming the SO-35 Parrot.
SO-35 in Mode B:
SO-35's other mode is Mode B, which is a more conventional crossband repeater mode. The input to this repeater is 436.291 MHz (again, watch that Doppler!), and the output, or downlink is on 145.825 MHz. This repeater is duplex, and it is strongly encouraged that you listen to yourself on the downlink. This enables you to monitor your own signal for quality, which is important for QRP stations. In addition, you can instantly know if you accessed the satellite, or got squashed in the dogpiles. As this is the most popular satellite and mode in Australia, keep contacts brief and to the point, as outlined in my article, Satiquette. The tips mentioned there are intended for a busy satellite like SO-35. Still, despite the crowds, this is a very enjoyable bird to work. Most operators are pretty good and will give a newcomer or QRP station a fair go. Note that SO-35 is not available full time, but is schedules by the operators. I maintain a copy of the schedule with pass information for VK/ZL/P29 operators here, or you can visit the home page using the links provided.
As for compensating for Doppler shift goes, there are two ways you can go about it. You can either use your VFOs, which has the advantage of using no memories, but may mean manually setting up for the pass each time, or you can store common frequency pairs on a series of memories. For SO-35, using a dual band rig with 5 kHz steps, a group of memories could be programmed as follows:
Personally, I use the VFO approach, but having the memories setup would be useful for a mobile operator. Note that channels 1 or 5 may not be required for some passes, depending on your location and the pass itself.
UO-14 was a digital bird until recently, when it was switched to operate as a Mode J FM repeater. Mode J is the opposite of SO-35's Mode B, in other words, 2m uplink and 70cm downlink. The frequencies are 145.975 for the uplink and 435.070 for the downlink. Operating UO-14 is similar to SO-35 in Mode B, except that unlike SO-35's strong downlink, UO-14 has a relatively weak downlink, and a directional antenna is recommended. UO-14 has a sensitive receiver and only a few watts will access the bird, so be _very_ careful and don't transmit unless you can hear it, otherwise you may cause QRM to people you can't hear. Also, unlike SO-35, UO-14 is relatively quiet. It is quite OK to have a short ragchew on the bird, but once callsigns have been exchanged, please leave breaks for other stations to join in. Again, most operators will give other stations a go and invite them into the QSO, or if things get busy, to work other stations. When things are quiet, a ragchew can alert other operators ahead that the satellite is approaching. I keep a list of UO-14 passes online, with details for Melbourne.
Again, like SO-35, you can program a series of memory channels to make it more convenient to operate UO-14. The frequencies to use are as follows:
Note that channels 1 or 5 may not be required for some passes, depending on your location and the pass itself.
RS-13 is a Mode A (2m up, 10m down) and Mode K (15m up, 10m down) linear transponder. Unlike the FM birds mentioned previously, there is no fixed channel, but instead a band of frequencies in the 2 and 15 metre bands are translated to 10 metres. To minimise bandwidth and use transponder power most efficiently, SSB or CW mode is normally used (FM is definitely _NOT_ welcome here!). Due to the dual uplinks, it is best if everyone adjusts their uplink to compensate for Doppler. For Mode K operators, this goes against the normal convention of adjusting the highest frequency, but avoids needless confusion, especially when a Mode K station is talking to a Mode A station. The passband for RS-13 is 21.260 - 21.300 (Mode K uplink) on 15m, 29.460 - 29.500 on 10m (downlink) and 145.960 - 146.000 on 2m (Mode A uplink). The transponder is "non inverting", which means that if you transmit USB, your signal will come down on USB as well, and if you are near the bottom end of the uplink, your downlink will be near the bottom end of the band. Also, please do not use any more power than is needed to make your signal as loud as the beacon. The transmitter's power needs to be shared among several users, and keeping your signal to the level of the beacon ensures there is enough to go around.
When using RS-13, listen for the beacon around 29.458 MHz (+/- Doppler). Once you have the beacon, pick a clear spot in the 10 metre band, then adjust your uplink frequency so you can hear yourself on the downlink. As other stations may need to find your frequency, it is worth making long CQ calls so they can find you in the passband.
Unlike in the Northern Hemisphere, RS-13 can be fairly quiet over Australia, so it is quite OK to have a ragchew on this satellite. In fact, most of my CQ calls go unanswered! :( ).
During the entire pass, you will need to tune your uplink to compensate for Doppler. If you're using 2 metres, the amount of shift is considerable (up to 6 kHz total from start to finish of a pass), and tuning while transmitting is a must.
FO-20 and FO-29 (Mode JA):
These two satellites are very similar to each other, and they even share the same analogue passbands. FO-20 is constantly in Mode JA (2m uplink, 70cm down CW/SSB), while FO-29 rotates Mode JA, Mode JD (digital) and digitalker mode. To work these satellites, you will need both 2m and 70cm all mode equipment. The 2m box needs to be a transceiver, but on 70cm, you can use a receive converter with an HF receiver, if you prefer. However, if you can afford a transceiver, go for it, as 70cm is an interesting terrestrial band, and there are satellites which do require 70cm on the uplink. Again, please do not use FM on these birds, and keep your signal down to the same strength as the beacon or less.
FO-20 and 29 are quite sensitive, and with portable beams, it only requires a few watts to get the full allocation of transponder power. A fraction of a watt into a beam will give good QRP CW contacts! The biggest issue with the two FO satellites is the +/- 10 kHz Doppler shift on the downlink, which requires constant attention to the tuning knob. Also, the transponder on these satellites is inverting, which means that you need to transmit on LSB to get USB on the downlink, and the top end of the uplink passband corresponds to the bottom end of the downlink passband, which can be very confusing, especially when trying to correct for Doppler shift!
To work the 'Fujis', find a clear spot on the downlink, then find the corresponding uplink frequency. You will probably have to tune the uplink to hear the signal come back down. Once you have found your uplink, all further tuning is done on the downlink. Remember that for SSB use, transmit using LSB to get the normal USB downlink. Long CQ calls are a good idea, and as with RS-13, these birds are very quiet, so feel free to have a good ragchew when it's over VK/ZL.
Finally, here's the passband information for Mode JA on FO-20 and 29.
Beacon - 435.795 MHz.
Uplink - 146.000 - 145.900 MHz (note the inverted notation!).
Downlink 435.800 - 435.900 MHz.
There are a number of satellites that can be worked with modest gear, and you can have a lot of fun. While it's possible to spend a lot of money on a top satellite station, it's certainly possible to work satellites on much less, possibly the gear you have in the shack now! Perhaps that handheld you never fire up, or the old HF box gathering dust in the corner might have a new life as a satellite rig. :-)
Good luck and Enjoy!