Hi everybody,
I'm setting up a portable satellite station to work the linear and FM birds. The equipment is a Funcube Dongle Pro+ for RX (with a diplexer to avoid desensing), an FT-817ND for TX and a homebrew handheld yagi similar to the arrow satellite antenna (3el on 2m and 6el on 70cm, DL6WU spacing). I use computer control for Doppler on both RX and TX.
I'm quite a newbie to the satellite world and yesterday it was the first time I managed to hear myself on the downlink of some satellite, after a few unsuccessful attempts (in which I also had to cope with bad weather). It was on FO-29, at about 17:00UTC, 4th February (my locator is IN80do). I'm quite excited about it. Hopefully, next time I will be able to work some contacts.
I have some impressions and some questions on operating tips that may be useful. The first impression is that it's very nice to use an SDR with Doppler correction for RX, because I get to see the full passband of the transponder and the beacon of the sat, and the frequencies I see at my screen are the frequencies as transmitted by the satellite. I can see the Doppler of the satellite by looking at how local spurs sweep up across the band, and I can also check the precision of my TLE's by checking if the beacon drifts. This time it was rock solid.
It also seems that most people tune only their receive, since the QSOs slowly get higher in frequency. This is probably the most sensible thing to do if you're not using computer Doppler control, because FO-29 is V/U. I've also seen that most people crowd the centre of the passband, at about 435.850MHz. FO-29's transponder is 100KHz wide but I've heard that the downlink is stronger near the centre of the passband. Does anyone know how much the difference is or if this hardly matters at all? Also, since I'm using full Doppler control, is there any suggestion for a frequency on which to call CQ? If I'm just next to a station which is tuning only the downlink, I will be run over when he goes up due to Doppler shift, so I have the impression that I'll be probably better at something like 435.840MHz, with most people above me. Or is this lower part of the passband for CW? Of course this question is only for FO-29. It doesn't apply to AO-73 because its passband is only 20KHz, so there is not much free room usually.
Another nice thing of the SDR is that I have it calibrated to report signal strength in S-units (with S9 = -93dBm) in a more or less accurate way. This way, I can see that my noise floor is S2, the beacon ranges between S3 and S4, and strong stations are S5 to S6 in the downlink. Would you guys consider it useful if I use this "true" measurements when giving signal reports? I hear that most people go with 59 or 58 or nothing at all, but keep in mind that with my setup a report of 56 really means 12dB above the beacon, and nobody will likely be 59 if that's at all possible, keeping in mind the power of the satellite and the path loss equation.
My own downlink had about the same signal strength as the beacon. I guess that's about right to make plenty of contacts. I also read somewhere that you should adjust your power to be about the same strength as the beacon. I keep hearing stations much stronger than the beacon, so I guess that it's not practical for everybody to measure their downlink strength or lower their power.
I also heard people working some stations that for me where completely in the noise for me, so I guess these people have much better RX equipment than me. Those of you with good RX, could you provide an accurate measurement of strength of the beacon for you so I can compare with my own measurements?
Another thing that I observed is that there were FM signals on two frequencies being repeated by the transponder. This had the Doppler shift that a fixed frequency 2m signal will have when repeated by the satellite. One of the signals had CTCSS while the other didn't. The signals where two weak to copy, but it seemed that the language was Spanish. It seems that it people talking on FM simplex about 145.985MHz. Does this happen often? It's a pity that people don't follow good operating practices.
Finally, sorry for the long post, and in case anyone wants it, I have a full SDR recording of the pass. I will usually be recording the SDR when I'm working satellites, so if anyone finds these useful, please let me know.
Hope to work you soon on the satellites.
73,
Dani EA4GPZ.
Dani,
You have an excellent satellite station comprised of the Yaesu FT-817ND and FUNcube Dongle Pro+. It should provide hours of enjoyment through experimentation of SDR technology. I call my similar station "the poor man's Flex radio."
For a period of several months, I experimented with using the Dongle as my SDR TX and used a Yaesu FT-857D. I was using the HDSDR software configured for Kenwood CAT control within SatPC32. The FT-857D was configured as the transmit radio -- also via CAT control.
During this time I learned to appreciate full CAT control with the SDR. You can manually tune while listening on SDR; however, having full control makes it easy to move around the transponders' passband. On all birds except for AO-73, I was able to use full-control all of the time.
Your observation of FO-29 and operators' Doppler shift compensation is correct. Many stations who do not use computer Doppler correction only tune the downlink. This is common and the generally accepted practice. It is not a perfect system by any means. If people would spread out a little bit more and not try to call CQ 2 kHz apart from the next station, less collisions between QSO's would occur. My recommendation is to not call CQ within 5 kHz of the center because that's where everyone goes by default. Most radios and computer SDR programs are very user-friendly for VFO tuning, otherwise they are not useful for radio operators. The lower part of the passband is generally where you will find CW.
Your observation of AO-73 passband behavior is correct. There's not as much free room but it is adequate for multiple QSO's so long as people adjust for Doppler shift correctly.
If your SDR is calibrated well, the S-unit report might be accurate. Generally, I try to not be stronger than the beacons. That can be difficult at times. If you have many users with high power, your signal will not be heard. Some stations cannot hear the beacon because of multiple issues (their antenna, feedline, etc.) and compensate for this by driving up their power. It is a great tool to use your SDR software to identify who is driving the transponder hardest. You can easily spot stations with a wide signal.
FM: I cannot speak for the EU, but in the United States, it is very common to see some FM coming from the south. It is non-ham traffic. I never hear call signs -- just a lot of foul language. Sometimes I have seen repeaters from 146.00 MHz on the FO-29 passband.
Occasionally a ham on 2m meters will stray into the satellite portion of the band and I will record their FM conversation perfectly via FO-29. I have emailed and spoken with a few of these individuals. They were unaware that simplex in that portion of 2m could be heard by satellites in space! It is very useful to make AF+RF recordings of a satellite pass for later reference.
I am aware of two stations today in the United States who are regularly using SDR in their portable stations -- one with a tablet and one with a laptop PC. I suspect we will see more of this during Field Day. I know that it will be my preferred configuration!
73 Clayton W5PFG
On Thu, Feb 5, 2015 at 8:24 AM, Daniel Estévez daniel@destevez.net wrote:
Hi everybody,
I'm setting up a portable satellite station to work the linear and FM birds. The equipment is a Funcube Dongle Pro+ for RX (with a diplexer to avoid desensing), an FT-817ND for TX and a homebrew handheld yagi similar to the arrow satellite antenna (3el on 2m and 6el on 70cm, DL6WU spacing). I use computer control for Doppler on both RX and TX.
I'm quite a newbie to the satellite world and yesterday it was the first time I managed to hear myself on the downlink of some satellite, after a few unsuccessful attempts (in which I also had to cope with bad weather). It was on FO-29, at about 17:00UTC, 4th February (my locator is IN80do). I'm quite excited about it. Hopefully, next time I will be able to work some contacts.
I have some impressions and some questions on operating tips that may be useful. The first impression is that it's very nice to use an SDR with Doppler correction for RX, because I get to see the full passband of the transponder and the beacon of the sat, and the frequencies I see at my screen are the frequencies as transmitted by the satellite. I can see the Doppler of the satellite by looking at how local spurs sweep up across the band, and I can also check the precision of my TLE's by checking if the beacon drifts. This time it was rock solid.
It also seems that most people tune only their receive, since the QSOs slowly get higher in frequency. This is probably the most sensible thing to do if you're not using computer Doppler control, because FO-29 is V/U. I've also seen that most people crowd the centre of the passband, at about 435.850MHz. FO-29's transponder is 100KHz wide but I've heard that the downlink is stronger near the centre of the passband. Does anyone know how much the difference is or if this hardly matters at all? Also, since I'm using full Doppler control, is there any suggestion for a frequency on which to call CQ? If I'm just next to a station which is tuning only the downlink, I will be run over when he goes up due to Doppler shift, so I have the impression that I'll be probably better at something like 435.840MHz, with most people above me. Or is this lower part of the passband for CW? Of course this question is only for FO-29. It doesn't apply to AO-73 because its passband is only 20KHz, so there is not much free room usually.
Another nice thing of the SDR is that I have it calibrated to report signal strength in S-units (with S9 = -93dBm) in a more or less accurate way. This way, I can see that my noise floor is S2, the beacon ranges between S3 and S4, and strong stations are S5 to S6 in the downlink. Would you guys consider it useful if I use this "true" measurements when giving signal reports? I hear that most people go with 59 or 58 or nothing at all, but keep in mind that with my setup a report of 56 really means 12dB above the beacon, and nobody will likely be 59 if that's at all possible, keeping in mind the power of the satellite and the path loss equation.
My own downlink had about the same signal strength as the beacon. I guess that's about right to make plenty of contacts. I also read somewhere that you should adjust your power to be about the same strength as the beacon. I keep hearing stations much stronger than the beacon, so I guess that it's not practical for everybody to measure their downlink strength or lower their power.
I also heard people working some stations that for me where completely in the noise for me, so I guess these people have much better RX equipment than me. Those of you with good RX, could you provide an accurate measurement of strength of the beacon for you so I can compare with my own measurements?
Another thing that I observed is that there were FM signals on two frequencies being repeated by the transponder. This had the Doppler shift that a fixed frequency 2m signal will have when repeated by the satellite. One of the signals had CTCSS while the other didn't. The signals where two weak to copy, but it seemed that the language was Spanish. It seems that it people talking on FM simplex about 145.985MHz. Does this happen often? It's a pity that people don't follow good operating practices.
Finally, sorry for the long post, and in case anyone wants it, I have a full SDR recording of the pass. I will usually be recording the SDR when I'm working satellites, so if anyone finds these useful, please let me know.
Hope to work you soon on the satellites.
73,
Dani EA4GPZ.
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participants (2)
-
Clayton Coleman -
Daniel Estévez