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RE: About (HAMSAT) VO-52 Beacon



Hi William,

Thanks so much taking the time to clear up the cause of the beacon's
interesting "signature." After your explanation of the derivation of the
beacon, I fully understand what's happening. Your post also cleared up the
frequency shifting noticed by several.

As I mentioned in my last post I concluded that it was caused by too much
uplink power. Bruce, VE9QRP posted that he actually feels it's a "feature"
that he uses to tell when the transponder is being used. Perhaps this
discussion will encourage some to back off a bit on the uplink power.

Please understand that my critique of the signal was meant to understand
what was happening and not to reflect negatively in any way on your splendid
accomplishment and I can't overstate my sincere appreciation for the effort
you went through to give us another fine "linear" transponder

Best regards and 73s...Bill - N6GHz

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of William Leijenaar
Sent: Friday, November 25, 2005 7:04 PM
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] About (HAMSAT) VO-52 Beacon


Dear AMSATs,

I wish I had the same free time now as when I designed
the HAMSAT and P3e transponder. Unfortunatly these
times have been changed (for the moment) due to QRL
things.

However, I often try to be QRV on the HAMSAT and check
the signals from my transponder and read the messages
on amsat-bb. I just read about the beacon "problem".
The "problem" with the beacon is actually not a
problem but it is known. The beacon signal is injected
at the IF, and runs throught the transponder from the
IF section, up converter, via the final PA to the
antenna.

The changes you hear on the beacon frequency is caused
by the amplitude limiters in the IF that are activated
by a too strong uplink signal. These limiters are only
for protection, to avoid that the IF and VHF
amplifiers get overloaded and generate all kinds of
unwanted signals at the output.

My transponder is straight forward to keep it physical
small and cheap in cost (as I had no sponsors). Unlike
most other transponders my transponder on HAMSAT has
no AGC system. It gives always maximum gain with
maximum sensitivity. The main reason is that the AGC
systems I had didn't fit in the small sized box. As an
option I choose for limiters, and it worked great in
tests.

Secondly, I tought limiters might be helpfull against
aligators. To deal with too strong signals most
transponder have an AGC to lower the RX gain, and
actually be helpfull to the alligators.
With the limiters their SSB signal will get distorted
and they might lower their powers to have better audio
quality.

The change in beacon sound is an indication for too
much uplink powers and will be heared mainly in areas
where higher powers are available on the uplink, like
US, Europe, Japan...

Its funny to know that nobody here has discovered that
the bandpass is shifted some down in frequency...
There is no technical failure, the reason is known
here...
No panic please :o)

Please keep in mind that this transponder is my privat
work and privat money. Frankly speaking this is my
privat transponder I "give" to the amateur world. I
was one of those many poor students, and this was the
best I could do with my resources I had available at
that time... The whole thing is just 16cm x 10cm x 3cm
!! even smaller than the professional Indian
transponder :o)

I hope you all enjoy my transponder even when it is
not perfect,

73 de PE1RAH
William Leijenaar
---
Access over 1 million songs. Try it free.
http://music.yahoo.com/unlimited/
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