Friday, April 08, 2011

70MHz FM update

You'll recall that I've mentioned a few times the mysterious 'hum' that appeared on my 70MHz transmissions. Several times this seemed to be down to poor SWR because of a frozen aerial, another time a poor power connection, a further time a cat had knocked the negative supply to the rig from the PSU. Then it happened again last week and I couldn't really decide what the cause was.



Since I had recently acquired a converted Ascom SE550 rig for 70MHz I decided to use that instead. Got it all connected up and it seemed to work ok. I was very pleased of Andy, G0BEQ's manual which helped me set up the memories, configure the squelch, dispose of the roger beep (!) and generally tweak the rig as I wanted it.

However, Julie complained (quite rightly!) that the audio from the rig was particularly loud, even at minimum setting. Loud squelch bursts were clearly audible downstairs away from the shack! To get over this, I have done a rather crude (but effective) modification of putting a 100k pot in the speaker lead and using that to trim the audio level.

The converted SE550 seems to be working alright. There was a little tropo around on 70MHz yesterday and I was surprised that distant stations were being heard through the Tring Parrot, MB7FM - stations from as far afield as Clacton on Sea and Portsmouth. Sadly, I couldn't hear them direct, although there was just a hint of G3VXM from Portsmouth.

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