[amsat-bb] First impressions on FO-29
daniel at destevez.net
Thu Feb 5 14:24:23 UTC 2015
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
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.
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