[Elecraft] Elecraft: RFI Problems

[Martin.Evans at simoncarves.com]

Sorry this is "off topic" but there is so much experience here. I've been
licensed for only 2 years, my only rig is K1 so I've been QRP CW only (and
enjoyed it immensely). I've recently started using a PA to get up to 100W
on 3.5 to 21MHz, but RFI problems have started to appear. Here are the
symptoms:

50Hz hum on key down on hi fi
Similar problem on mains MW radio.
Freezing of PC modem on key down.

These are all in different rooms of the house and all at least 15 feet away
from the rig.

The rig is on the ground floor right next to the outside wall where the
coax feeder runs out at ground level. Feeder is about 70 feet long and all
at ground level until it rises to a multi dipole at 30 feet up, cut for
80/40/20m. Feed point is at least 50 feet from house. The feeder shield is
connected directly to the PA ground point and therefore to the mains ground
wire. I have no Balun and no RF ground so I guess I've broken all the
rules.

I suspect RF is on the mains 240V house wiring and can see it on my scope
(about 5mV P-P superimposed on the mains). I have a number of things to try
but not sure in what order of priority, maybe someone could help, I want to
tackle the source of the RFI first, rather than the affected domestic
equipment.

Here's the list:
Make a coax choke balun in the feeder to reduce out of balance currents
(quick and cheap)
Fit a commercial balun (heavy and pricey)
Construct an RF ground in the garden and connect to feeder sheath at entry
into the house. (time consuming)
Fit a ferrite ring choke to the PA mains lead
Build an inductively coupled ATU to avoid connection of feeder sheath to
the mains ground.
Fit ferrite ring chokes to the affected equipment
Fit a proprietary RFI filter to the telephone line (to cure the modem
problem)

Or maybe I should just go back to QRP hi.

Any advice would be greatly appreciated as I don't want to run the risk of
causing RFI to the neighbours.


Why not take a look at our Web site?
http://www.simoncarves.com

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