[amsat-bb] Why too much uplink power is bad/eggbeater antennas on xmit

John Brier johnbrier at gmail.com
Mon Aug 3 00:07:39 UTC 2015

Sorry to hijack this, but I have a question about this "And I explained why too
much uplink power is bad for both FM and linear sats, in terms of bandwidth
and power consumption on the satellite."

I understand why it's a problem on linear satellites, but why is it
also a problem on FM sats?

John Brier, KG4AKV

On Sun, Aug 2, 2015 at 7:53 PM, Philip Jenkins <n4hf.philip at gmail.com> wrote:
> The discussion on uplink power fits right in with a conversation I had last
> weekend...
> While I was not wearing my AMSAT badge at a hamfest on July 25, a married
> couple - both hams, both fairly recently licensed - recognized me from a
> previous hamfest when I was wearing that badge. Their question for me was
> to why they could hear  (a) satellite(s), but no one could hear them...
> The satellite in question is SO-50 (and I did take a few minutes explaining
> the difference between linear birds and FM-only ones).
> Before the OM joined us, his YL told me that her husband doesn't want to
> use antennas like the Elk or Arrow, even on a tripod. I then suggested to
> her that he consider a fixed elevation mount, so as to only have to track
> the azimuth.
> Then the OM showed up. He doesn't even want to consider the
> fixed-elevation, because he'd still have to track . I suggested he leave
> the tracking to a computer...still not acceptable
> He then explained that they spend a lot of time in a motorhome. For his
> antennas now, he is using eggbeaters. On the 440 receive side, he is
> thankfully using a pre-amp, so he can hear adequately,
> For the transmit, he is using 50 watts into an eggbeater, and still can't
> be heard on the satellite. He told me one recommendation he was given was
> to increase the xmit power to 150 watts (*I visibly shuddered*) so as to
> overcome the non-directionality of the eggbeater. (And I explained why too
> much uplink power is bad for both FM and linear sats, in terms of bandwidth
> and power consumption on the satellite.)
> On further questioning, he knew about the PL tone to turn-on SO-50, but
> didn't know about the different PL to actually access the satellite on each
> transmission. I explained to him that it is like terrestrial repeaters; no
> matter how much power you run, the repeater won't "hear" you unless you
> transmit the PL every time.
> In a follow-up email the next day, I passed on the SO-50 operating guide
> (PDF) from the AMSAT website, and advised him to try programming his radio
> with the proper PL and frequencies for adjacent memories BEFORE consdering
> increasing transmit power.
> I really think his problem is not using PLs, rather than inadequate power
> levels on an omni antenna.
> My question is two-fold (I still need to follow-up with him). 1) For those
> of you successfully using eggbeaters for the uplink (and he is adamant
> about not using a yagi, despite my advice that the performance will suffer
> quite a bit with eggbeaters), what output power do you typically use? I
> think 50 watts into an eggbeater is probably still too much power,
> considering 5 watts into an Arrow is usually enough for successful
> communications.
> 2) I know that various power levels are suggested for various gain
> antennas, but I'm wondering what the suggested EIRP is for successful - not
> ones which would hog the satellite  - uplinks.
> Philip N4HF
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