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Thursday, 7 November 2013

Ouch - That's Noisy!

Well,

You may remember the radio I acquired a while ago, back here:

http://g0mgx.blogspot.co.uk/2013/10/another-one-really.html

And the trials and tribulations I have had over a suitable PSU for the PA in the radio. Well, eventually I have received a unit I bought from China. It's stuck in a box and looks like this:


Now, currently this SMPS is generating some horrendous noise from about 4MHz to about 6.5MHz (and probably in other places as well!). The noise is only audible on any of my radios with an antenna connected; nothing with the antenna connector pulled out.

There is a very bad example of the noise on the 60MHz CW frequency 5.373MHz, however if I stick the antenna into the Spectrum Analyser, I don't see anything different with the SMPS on or off, the trace is the same:


Odd, egh?

** UPDATE **

I conclude that the SA is nowhere near as sensitive as a HF receiver - hence the trace above doesn't show the QRM.

Anyhow, following some exchanges on the RSGBTech Yahoo Group, I've had some great advice from some SMPS wizzos and we ended up removing the earth from the SMPS board itselt (don't try this at home) and connecting the -ve power rail to the metal case and hence the mains earth.

Result? Problem solved - the noise has been eliminated.

The RX On the 1000MP is excellent, I've rearranged the shack to accommodate the radio a little:


The photo above was taken with the panoramic feature of my Nikon Coolpix - good egh?

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