Chris: John, W1TAG, has an LF mains filter on his web site, but it is
designed for 120VAC service, so you have to rate components appropriately
for your higher EU mains voltage....(usual X1/Y2 X2/Y2 capacitor precautions
apply). I had a noisy APC uninterruptible power supply and John's filter
design helped my situation on 137 kHz...
http://www.w1tag.com/SWITCH_FIL.htm
Consider the possibility of RF rectification occurring on either the input
or output side of the TV preamplifier, possibly at the antenna connections,
coaxial connections to preamp input, etc., as oxidation could be the
culprit. Coaxial "F" connectors can be prone to center pin and outer
threaded barrel oxidation. I use 75 ohm RG6 coax and F connectors for my
LF/MF EWE antennas and regularly apply some intermittent DC "sealing
current" (24V through 100 ohm resistor) to keep the connector resistance
low. I see a few ohms difference before and after if I leave the antennas
alone for a week or so without sealing current treatment. Any time I notice
some IMD products at LF it is usually F connector oxidation that is the
culprit....
Connectors with gold or palladium center pins (and shells) help in that
regard...
73 Mike wa3tts
----- Original Message -----
From: "Chris Wilson" <[email protected]>
To: <[email protected]>
Sent: Wednesday, May 18, 2016 12:04 PM
Subject: LF: Can LF damage a mains input filter?
18 May 2016
Long story, but since stopping LF 136kHz TX for a while in lieu of
some HF working all the digital TV's in the house freeze or totally
blank on all bands above top band, up to 50MHz when I transmit at more
than about 5 or 10W. I have a loft mounted UHF TV aerial feeding an
amplifier cum distribution box. It has an internal mains PSU. Without
it we receive hardly any channels. It's been fine for years, and I
have never had TVI. My HF set up is unchanged from when I had no
issues. I put the TV antenna co-ax direct into my SA and on circa 531
MHZ see a broad digiTV signal that's strong. If I TX on say 20 meters
at high power into my antenna I see zero change in the TV signal. I
have also fed the output of my HF TX (TS-590 Kenwood) into the SA via
an attenuator and the output looks spotless on all bands. However, if
I connect the TV aerial amp / distribution box up and look at the
output from it the TV signal immediately drops into the noise when I
TX. My neighbours have no issues at all.
This seems to have occurred since I have been active on LF, and I had a
stage where full power would trip the main RCD in the consumer unit,
so RF was getting into the mains. Is it conceivable something has
occurred to perhaps a mains filter in the TV amp? I looked inside the
plastic case and it has a small mains transformer that feeds feed
throughs into a screening can with all the RF stuff within it. If
there is any mains input filtering it must be on the low voltage side
of the transformer. The unit has a moulded on three pin mains plug, but
with a plastic earth pin, so the unit is not grounded.
Is it possible to make a mains input filter for a piece of equipment
that would filter 136kHz but not affect normal 50Hz mains operation?
Has anyone experienced anything like this?
I have ordered a new amp / distribution box of known make, and will
just try replacing it, but would also like to know if my LF activity
could have done this?
Thanks.
--
Best regards,
Chris 2E0ILY mailto:[email protected]
My part time LF grabber is at
http://www.chriswilson.tv/grabber.html
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