Re: Ground noise on 23cm?

Paul G8AQA

I had a lot of wideband noise particularly in one direction. I temporarily put in a switchable bandpass filter before the Bulgarian SG Lab masthead preamp. In the worst direction the drop in background noise with the filter in was about 24dB.  It is now in permanently.  It was a surplus silver plated interdigital filter that I modified to increase the frequency.  The loss was too small to measure reliably.

Paul G8AQA

DBN wrote:

I've used one of John's filters for ages. Through loss is tiny, something around 0.15dB increase in NF when I put it in front of a DDK preamp on my HP8970B compared with an SMA barrel connector.

I am 51km LOS from Emley Moor and there are no cellphone masts within 2km, but the problem was severe. I had about 15 noise spikes in many directions before I added the interdigital filter. It has SMA connectors.

Neil G4DBN

On 17/09/2020 10:05, Anthony Coldman via wrote:

Morning all


I would agree with others that a filter in front of a preamp is an almost must now, I have built ones for 23cm and 13cm using the information on this site and the difference is night and day, If you prefer to buy you can also have a look at PE1RKI site he produces nice filters as well.




Anthony G7LRQ

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