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Re: [IRCA] Help Needed - QRM
Michael Yule wrote on the 9th of June,
"Hi all - I am setting up my station finally at my new home, but I seem to
have a QRM problem that I haven't run into before and I'm hoping that
someone can provide some advice. I have pretty much entirely cleaned up any
interior RFI problems, although to be sure there can be a little hash from
the laptop when it is too close to the RX. Other than that though it is
pretty much silent inside the house as heard on my ICF2010 with no external
antenna connected, and scanning across all the bands.
I have a Wellbrook 330S (I originally bought it for tropical SW years ago,
but I'm thinking of changing to a 1530S+) and a modified ICF2010 fed by 100
ft of new Bury Flex with BNC's. The location is about 600 ft up a steep
slope above Howe Sound at Lions Bay (maybe 1/3 mile inland from the shore)
facing south west by west. Should be DX paradise. Unfortunately however I
have some RF noisy neighbours, and I'll deal with that as I can. The problem
is that I'm getting a continuous 5 or 6 LED's lit with noise on pretty much
every band (not below 3 Mhz because the 330S has reduced sensitivity below
that). Part of the problem is that I can't find a recording of what 'normal'
QRN is, so I can't even tell whether a good portion of the noise I'm hearing
is aurora/thunderstorms/etc or whether most of it is man-made. When I take
the Sony to where the antenna is (on the ocean side of the house, about 4 m
away from it) and just use the wbuilt in whip for direction finding of the
noise, th!
e biggest radiator seems to be the antenna and the coax itself, although I
can also hear some QRM from the neighbours. I'm not supposed to ground the
shield on the loop, and so I'm not sure what to do next. A counterpoise
under the loop? I sent an email to Andy at Wellbrook asking if my 16' metal
mast and 3' pole above the rotator could be causing problems, and I'll be
interested in his perspective on this. I have actually disconnected the
rotator cable because it was radiating crap unto the coax as well, and I
guess I'm going to have to look for some shielded rotator cable. But I think
something else must be going on, and I'm hoping maybe someone can offer some
suggestions. I asked Anduy if maybe the loop head had deteriorated, or maybe
there's something else, but I'm at a bit of a loss I'm afraid - maybe the
BNC's weren't put on right, I dunno! Thanks for your help - I've been
offline for a year while we moved and renovated, and I want to get this
right - I miss spending ! time at the dial. "
Michael,
Getting rid of QRN is a bit "hit and miss". It is possible that you may have
conducted power line noise radiating for the loops feeder and the rotator
cable. So I would recommend that you fit a mains filter to the
receiver/antenna power supply and the rotator controller. The mains filter
should one with an Earth line choke, so that the ground connexion of your
equipment is RF isolated from the power earth. If you can tolerate a small
loss in gain above 14MHz, then place the loop close to the ground. This will
prevent the loop from picking up noise from under the antenna. I wouldn't
expect the metal mast to be problem. If you still suspect that the loop
amplifier is faulty, you can purchase either a new amplifier that slots into
the old loop or replace the loop only. You can convert the 330S to an 1530S+
just by changing the amp. or the loop. The Amplifier Interface is the same
for both loops.
Kind regards
Andrew Ikin
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