[amsat-bb] RE:

[Tony Langdon <tlangdon@xxxxxxxxxxxxxxxxxx>]

> I am one inexperienced newbie on the satellites.  I am just 
> trying to learn 
> how to use them and need some advice from the gray-hairs.

That's what this list is all about (not all of us are grey, hopefully that's
years away for me! ;-) ).

> As I have related, I first used the FM satellites with a 3 
> watt handheld, 
> and was able to make nice contacts when I slipped a word or 
> two in-between 
> guys that might be using a bit more.  When I bought my 
> FT-847, I admit that 
> I pushed more like 10 watts into the antenna, and (shame on 
> me) it made it a 
> lot easier to be heard.  Fewer of the stations stepped on top 
> of me.  I got 
> my 2-3 contacts in and left the rest of the pass to others.

I typically run 1.5-4W into a small beam on FM, so 10W is a bit overkill.  I
have run more, but that was only for special event stations, and under
circumstances where the accuracy of the antenna pointing could not be
verified (manual rotation and a lot of approximations - you guys should see
those demonstrations, quite a lot of fun to get it all happening :-) ).

> This puzzled me.  Then I think I began to understand.  I 
> believe (but have 
> not yet tested it by dropping to 5 watts or so when the bird 
> is well above 
> the horizon) that I may be overdriving the receiver on the 
> bird and it can 
> not send me a reasonable signal back.  I hear myself, but the 
> signal is 
> clipped and sounds like I have not found the right receiving 
> frequency.  But 
> there seems not to be ANY right recieving frequency.

It could also be a local RF overload issue as well, but I have done some low
power tests using short bursts of carrier and an FM receiver.  At around 2W
carrier, the received signal when FO-20 is > 20 degrees elevation is quite
good, on a par with the beacon, one _could_ hold a comfortable FM QSO on it
(but you wouldn't want to hog the transponder bandwidth and make yourself
unpopular :) ).  Certainly, SSB or CW would be no drama.  Dropping the power
to 0.25W resulted in a noisy carrier, but even FM would have been copyable.
CW sould be Q5, and SSB quite readable.

So, from my tests into a 2 element Yagi seem to indicate that 50W is way
over the top, and a better Rx antenna/preamp would be the way to go.  

However, keep in mind that being portable, I have the ability to adjust
polarization to match the satellite exactly, and in real time (twist of the
wrist :) ).  Over time, I have proved this to be worth several dB is path
gain (in theory, the average, assuming random polarization from the bird is
3dB each way, but with full adjustment, I need much less fade margin, as
polarization related fades are practically nonexistent for me).

> 
> If I am overdriving the bird and disrupting my received 
> signal, I may have 
> been causing the other ops in the pass band to have degraded received 
> signals as well. If I am at fault for disrupting your 
> conversation over the 
> last week or so, I appologize.

This is possible.  Depending on the design of the AGC system on board the
satellite, you could have affected everyone, or just a part of the passband,
as the satellite backed off to avoid overdriving the transmitter stages.

> Maybe some of the fades we hear on the bird are not due to 
> rotation and 
> phase change.  Maybe some of them could be due to 
> inexperienced ops like 
> myself.
> 
> Mea Culpa.  I will change my operating to much lower powers.

Well, at least you had the guts to say "I made a mistake, sorry".  Chalk it
up as a learning experience, we all make mistakes, and progress is made if
each mistake is a new one. :-)

Good luck on the birds.

P.S.  I still have to get my Fuji station sorted out.  Almost there, just
some level tweaking and a new Xtal on the 2m transverter. :-)
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