[amsat-bb] Re: AO-73 sometimes hard to access

Andy Kellner hawat1 at yahoo.com
Mon Nov 25 16:46:55 PST 2013


now, not at all. Nobody is gonna dismiss your problems / concerns. For the people who work SSB satellites, they know that it can be a tricky business to get it right. And if you add to this a more-or-less un-proofen, new satellite it can make it even more tricky.

Now to my observations to last nights 55 degree pass over VK4 (orbit #62, sat eclipsed):

- Linear Transponder was there. I needed to start with an uplink frequency 4.2 kHz. higher than specified. This offset kept increasing thru out the pass to about 5 kHz. at the end of the pass (thats in addition to the doppler correction).
- Made a brief contact with a VK3 station which had similar problems finding/keeping its signal. 
- Once the downlink has been received, the signal was strong at times, however I noticed significant variations in signal strength on the downlink.
- I observed the same variations on the telemetry transponder. The signal is nice and strong and easily decodable in one frame and barely audible the next. Almost if the sat switches back and forth between high power / low power ? Other explanation could be the satellite rotating. This effect is certainly there from larger birds such as AO7, but I am not sure if any rotation would make any difference from a tiny cubesat ?

Equipment: Full duplex Yaesu 847, doppler corrected with CAT/SatPC32 and automatic tracking antennas (Nova), mast mount pre-amps etc. 2013-066B keps used.

Andreas - VK4TH

 From: James Luhn <luhn at wt.net>
To: amsat-bb at amsat.org 
Sent: Tuesday, 26 November 2013 8:55 AM
Subject: [amsat-bb] AO-73 sometimes hard to access

I have had the same experience as Perry with AO-73 with regards to 
signal problems.  I have an IC-910 transceiver and a  M2 2mcp14 (2 
meters) and  M2 436CP30 antenna with a Yaesu G-5500.  I have the IC-910 
set to about 25 watts on UHF.  I have made one contact on AO-73.  It has 
taken me forever to get the doppler correct as I usually cannot hear my 
signal.    Last night my returning signal was extremely strong for about 
1 minute.  In comparison, the received signal from FO-29 is extremely 
strong so I am assuming that my UHF antenna is working fine.  Like 
Perry, I have never experienced this before.  At times AO-73 takes some 
very deep fades (telemetry). With such a small little cube, I would not 
think the satellite is blocking the antenna (although 4 inches is 
starting to get close to 435 wavelength.  The frequency offset confused 
me at first.  I just kept cranking up the frequency and there I was but 
very, very weak. I'm not gripping as I am having a blast.  Those of you 
with experience are probably getting a laugh at what I report.  I am a 
newbie to this satellite stuff and learning as I go and extremely 
excited to make even one contact.  Maybe the geese overhead are causing 
me some problems. :-)

...a ham for 50+ years and enjoying every minute of it!
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