50Hz spaced spurious reports

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g4enz
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Joined: 2008/11/08 - 11:23
50Hz spaced spurious reports

I have long had an intermittent issue with giving STRONG stations extra reports about 30dB down and 50Hz offset from their transmit frequency. I have long puzzled about the source of this.

I have two radios, an Icom 7700 and a Flex 1500. The Flex is the one I mainly use for WSPR though I can use the Icom when I want to make comparisons.

Whilst comparing my doublet and my Cushcraft vertical (R8), I used the Icom and Flex both monitoring signals on 40m. Some European signals were very strong of equal strength on each setup, BUT only the Flex was showing weak 50Hz images.

I decided to swap the antennas between the two radios and, guess what, the images moved from Flex to Icom. It appears that the extra signals were specific to my doublet.

The next test was to run Flex and WSPR and doublet using my Netbook computer, ALL running on battery power, and with the house power switched off. Guess what, I still get 50Hz images.

The local 11kV distribution transformer for my area happens to be across the road from my property and my doublet gets within 20m of this transformer. The Cushcraft vertical is about 60m away from the transformer.

I must be picking up 50Hz from the transformer and mixing it with received signals. I cannot think of anything else that fits the observations. I would be very interested to know if anyone else has had similar experiences.

So, to all those who get the occasions "extra spot", I apologise, the fault is probably mine.