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