About (HAMSAT) VO-52 Beacon

There have been comments that the CW beacon signal on the Dutch transponder has been sounding "raspy". The designer and builder William PE1RAH posted the explanation below to the AMSAT Bulletin Board.

The cause is stations running too much power on the uplink. Users are urged to reduce their power so they run no more than the minimum required for communications.

About (HAMSAT) VO-52 Beacon

I wish I had the same free time now as when I designed the HAMSAT and P3e transponder. Unfortunately 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 through 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 thought limiters might be helpful against alligators. To deal with too strong signals most transponder have an AGC to lower the RX gain, and actually be helpful 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 heard mainly in areas where higher powers are available on the uplink, like US, Europe, Japan...

It’s 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 private work and private money. Frankly speaking this is my private 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

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