Gary -
My RF environment is definitely a challenge. Several multi-kW FM radio
stations and three TV stations within 5-6 km line-of-sight. I implemented a
sharp OCI helical filter
<https://www.ocicom.com/index.php/amateur-radio/products/2-meter-bandpass-fi
lter> long ago. It worked wonders in keeping these sources from crippling
my receiver chain. The broadband noise that I have described does not come
from the directions of the FM or TV towers.
Michael
From: gwj@me.com <gwj@me.com>
Sent: Saturday, December 23, 2023 8:08 PM
To: rfi@contesting.com
Cc: <nlsa@nlsa.com> <nlsa@nlsa.com>
Subject: Re: [RFI] Sources of wideband hiss
At the W6TCP hilltop EME site, this exact problem occurs on 2m and also on
220 MHz whenever the array is level and pointed towards one of the nearby
towns. There is NO character or modulation detectible, just a broadband
increase in the noise floor. It was bad enough on 220 to cause serious
problems. The solution there actually surprised me. He upgraded the LNA from
a P220VDG (from DB6NT) with a fairly broad LC bandpass filter to one from
WD5AGO with a much sharper cavity bandpass. That change alone was worth
almost 20 dB in noise reduction! All I can figure is that there must be a
great many VHF transmitters out there and with our high antenna gain, some
kind of complex intermod was occurring but I really don't know. So I will
always cast some suspicion towards out-of-band sources, in addition to the
usual buzzing switchmode converters.
-Gary NA6O
What are some sources of wideband hiss? I'm talking about an unstructured,
apparently unmodulated many-dB increase in the noise floor across the 2m
band* No associated birdies or other noticeable signals, just a nasty
hiss.
I see it in the direction of high-voltage power lines 2km away and also
toward a couple of houses I just a few hundred meters distant. The
mechanisms of those sources are not necessarily the same of course. Ideas
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