[amsat-bb] AO-51 S band reception

Luc Leblanc lucleblanc6 at videotron.ca
Sat Apr 25 04:01:08 PDT 2009

On the current AO-51 S band downlink i notice the "always" present deep fades period during a pass as the S band antenna are Dual band L/S 
Open Sleeve (1/4 wave stub) it confirm why my actual linear "WI-FI" stacked yagi perform better than my BBQ grill and dish with circular 

Foliage and blocking structures "seems" to have a lesser effect on the yagi than on the circular polarisation antenna. On one QSO with 
Clare VE3NPC we noted that theses fades does not happen at the same time at our respective QTH (Ottawa and Sorel-Tracy) making the 
following excerpt quite accurate. 

>From down to earth web site: http://www.docstoc.com/docs/5178447/down-to-earth

Satellite antennas are usually whips or dipoles. The satellite may slowly tumble, changing the orientation
of the antennas. If you happen to be "off the end" of its antenna, the signal may be too weak to work. Even
if you remain out of its "null", the direction of the linear polarization of the satellite downlink signal
changes relative to you during the pass. If the polarization at some instant happens to be perpendicular to
the polarization of your receiving antenna, there is about a 20dB (100x) signal loss.

I think i will give up in the fades elimination fight 100X signal is nearly impossible to compensate at the receiving side. It is probably 
an AO-51 S band limitation. Could be the internet can be a solution if each station can feed their downlink audio on Skype or echolink it 
will be possible to listen on theses various downlink sources making possible to have a full pass reception as there will be always one 
receiving station out of the fades.

DSTAR on S mode

As the first DSTAR satellite transmission has been made on AO-27 i don't know if the same test can be perform on AO-51. If someone with 
DSTAR capabilities is interesting to "test" it on mode V/S  just let me know. Why on mode V/S it's because i will have to be in half duplex 
as my DSTAR  transceiver is a monobander. It is a very "dangerous experiment" here as i will have to manually TR switching between the VHF 
antenna and the downconverter line.

But it will be interesting to know if a DSTAR digital signal can passed through AO-51 first?  I can try to send a couple of CQ on the last 
mode V/S  evening pass listening what goes out too?


Luc Leblanc VE2DWE
Skype VE2DWE


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