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Re: AO-51 V/S tonight



At 10:52 PM 5/19/2005 -0500, James C. Hall, MD wrote:
>Tonight I rushed home after a meeting to try and catch AO-51 during that 75
>degree pass tonight. I had a Transystem 3731AA D/C with original output of
>123MHz. Thank goodness I had an old TH-77A that I had opened up the receive
>many years ago. I mounted things on a helix feed taken off my Primestar dish
>from back in the AO-40 days. Itís a 5 ½ turn helix mounted on about 3Ē
>square aluminum.  I had the whole thing set up on the back of my truck and I
>was going to try and uplink with my mobile rig.  I never got that far.
>
>
>
>Despite the great pass, signals were faint and in the noise.  It never fully
>quieted ­ not even close. I was tracking the Doppler effect, I thought,
>pretty well, but I never had enough receive to even think about
>transmitting. Iím working on a portable setup for a potential FD contact.
>Iíll try again tomorrow. Any advice / help would be appreciated.
>
>
>
>73, Jamie
>
>WB4YDL
>----

Jamie,

First off, I have yet to try hearing AO-51 on mode-S, so I have no
first-hand knowledge of reception characteristics.  

A few questions to ask yourself:
1)  You state that you "opened up" the TH-77A.  I assume you mean to
receive frequencies not standard to the radio.  Have you determined how
good it recieves at 123-MHz?  If not retuning was done it might be quite poor.

2)  How did you connect the s-band convertor to the helix:  directly or
thru coax?  These converters are not real low noise, so its very important
to connect them directly without using coax.  At 2.4-Ghz even a foot or two
of RG-8 will increase the noise figure significantly. 

3)  The 5-turn helix has quite bit of directivity (gain = 10-dB, about the
same as an 8-element yagi).  You need to point it.  Don't expect to point
it straight up for the whole pass.  I'm just wondering from your mentioning
mobile operation.

4)  Recheck all your connections, dc-voltages, IF cables.  If it has not
been used for some time one of these may the culprit.  Do you have a
2.4-GHz signal source?  Does it produce as loud a signal as when you used
it for AO-40?  Inspect the helix carefully for bad solder joints or corrosion.

5) Keep trying :-)

73's,
Ed - KL7UW  <new call>
===================================
BP40iq,  Nikiski, AK      http://www.qsl.net/al7eb
Amsat #3212
Modes: V - U - L - S
===================================
----
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