Do not overlook the amount of RF modulated by 60 and 120 Hz and harmonics
thereof that are exiting the 'box' (RF amp, radio, etc.) via the POWER CABLING.
While at Heathkit we nailed down an otherwise 'clean' carrier that ONLY sounded
dirty when monitored locally when the transmitter was running into a dummy load
in the lab. The spectrum analyzer showed modulated carrier coming out of the
radio on the power cabling BUT clean exiting the RF output spigot.
What one hears is AC modulated RF in that day and age. Move forward 30 years
and add switching power supplies into the mix plugged into the same AC power
bus.
de Jim WB5WPA
From: David Robbins <k1ttt@verizon.net>
To: 'Matt NQ6N' <matt@nq6n.com>; jim@audiosystemsgroup.com
Cc: rfi@contesting.com
Sent: Monday, September 25, 2017 1:13 PM
Subject: Re: [RFI] SO2R and 2nd harmonic
- Seemingly RF Flooding would not be helped much by stubs or bandpass
filters if the desired transmitted signal is interacting with a wall wart.
Thus it would seem that adding or removing stubs meant to filter the second
harmonic would not be likely to reduce RF flooding from a wall wart that
was being excited by the desired signal. Is this intuition correct?
yes
- How does one differentiate between transmitted broadband phase noise and
RF flooding? Are there signal characteristics that can help differentiate
the two?
One common one is that there is a sharp power threshold where it starts.
Listen to the second harmonic while only at 1w and start turning the power
up. if the noise suddenly increases you have something that is either
rectifying or doing something else nasty outside.
- I generally use LMR400 Flex coax in the shack and LMR400 once the coax
gets outside. How much impact is the leakage in the shielding of this coax
likely to have on my inter-station interference? At present, six runs of it
run in a bundle along the ceiling from the output of the amplifier in the
operating position over to the place where the coax leaves the shack.
Once outside the shack, each line has a loop in it and all of the loops sit
adjacent to one another near the box/panel where the coax enters the
building.
None. I use various forms of rg-213 and have never identified a coax shield
leakage problem... though I have found bad connector shield connections or
just plain loose connectors.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
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