Re: [IRCA] Help Needed - QRM
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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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