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RE: WiSP, AO10 & FM sats



> > Well.  I have quite a lot of things to ask.
> 
> Feel free to ask.  That way lots of people learn.

:-)

> > OK.  Item #2.  AO10.  I think I heard AO10's beacon yesterday but
> > haven't heard it before or since.  Also I cannot hear myself on the
> > downlink.
> 
> In the next paragraph you said you are using a 70cm 5/8 wave 
> ground plane
> for both 2M and 430.  That is a lousy antenna for the FM 
> satellites and it

With a short coax run, it is possible to hear the FM birds on a 5/8, but
it's very marginal, at beat.  A 3/4 wave will work better at high
elevations.

> would almost qualify as a miracle for you to be able to work 
> AO-10 with
> that.  Yes, it's been done with less, but under "normal" 
> circumstances, it

Generally, only possible at perigee under exceptional conditions.  

> would be very hard.  For example, I'm running 22 elements CP 
> with a tower
> mounted GAsFet preamp and I can't hear AO-10 part of the time 
> (even when
> it's working).

Now, that's a tough bird to work! :-)

> I don't know about WiSP, but as to measuring the blockage, 
> what I did is to
> make sure I keep current keps and the computer clock is 
> exactly correct and
> then over the course of may passes, record the elevation (as 
> reported by
> Nova - what I use for tracking) of LOS and AOS.  I now have a 
> chart that
> shows where the blockage actually is for 70 cm RF.  It's 
> quite accurate.

Interesting technique.  As I tend to operate manually, I can gauge the
blockage by observation.  Sometimes signals seem to make their way around
obstacles, sometimes not.  It depends on the pass.  I find I also have a lot
of success at low elevations by bouncing the signals off a nearby reflector,
such as a house, or even a brick fence!  Perhaps because these objects
sometimes have a better "view" of the bird than I have at that time.

> > One of my biggest problems is trying to sort out real 
> (wanted) signals
> > from the muck.  I seem to get some "birdies" as I have said before.
> 
> Most of us do to some sort or another.

Becomes worse at higher power.  Also depends on the quality of transceiver
in use.  I have no problems at the 5W power level from an Icom IC-T81A
(which has a very clean FM Tx), but 10W from the 2m transverter into the
same setup gived me all sorts of birdies to contend with.

> UO-14 passes are not that long so that should have been a 
> clue.  If you have

Indeed.  The longest UO-14 hangs around for is 15 mins on an overhead pass.
Also, Doppler shift should be evident within 5-10 minutes of AOS.

> directional antennas, it's easy to move the antennas away 
> from the satellite
> and watch the beacon or downlink go away.  If it doesn't then 
> it's not the
> bird.  Since you are running omni antennas, that technique 
> does not work.

Listening for Doppler is probably the technique with the fastest results.
Eventually, the downlink should drift away from the centre of the passband
and become distorted (for FM).  On SSB, Doppler shift should be evident
almost immediately (Whoa!  Why am I drifting so badly? ;) ).

> I gather you are running a multiband antenna with a diplexer. 
>  It would
> likely help if you had separate antennas and are able to keep 
> them well
> apart.

The idea someone else brought up of using a diplexer with the 70cm port
terminated with a 50 ohm resistor is a good one to minimise the 3rd harmonic
output at the antenna.  Might have to try that trick myself on the
transverter.  I have a number of network terminators, which are ideal for
this purpose (they're just a standard 50 ohm 1/2W resistor soldered into a
BNC fitting).

> As someone else suggested, move to near the top or bottom of 
> the passband
> for tests as there is seldom anyone there and you won't interfere with
> another conversation.
> Someone also suggested leaving your transmit alone and 
> dialing around the
> receive so your transmit signal does not pass over other 
> conversations.
> There are two schools of thought on that one.  One says to 
> dial around the
> receive and the other says to dial around the transmit to 
> find yourself.
> The argument for moving the TX is that while you likely will 
> sweep across
> someone else, it will only be momentarily and not much of a 
> problem, whereas
> if you leave the uplink frequency constant and dial around 
> the receive you
> may be transmitting right on top of someone else for a 
> somewhat extended
> period of time.

I tend to prefer moving the Tx for initial signal aquisition, for the reason
you mention.  The obvious assumption here is that the downlink frequency
you're listening to is clear (assumption here being you can hear the
downlink - have you checked the beacon? :) ), so you're unlikely to QRM
anyone else for more than a few seconds.
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