|[AMRadio] Station Grounding|
jcandela at prodigy.net
Mon Nov 5 18:51:35 EST 2007
Bill, KB3DKS Writes:
Antenna performance is not the issue. The coax fed dipole
is resonant at the 75 mtr AM area. Some RF in the shack is inevitable
with the dipole about 20ft over my head. Not an issue.
What I am concerned with is the advisability of seperating the house
earth from the station (RF) earth.
With heating season here the oil burner for the first floor business
has a new solid state high voltage ignitor that generates considerable
phase control noise visable on the AC line and this happens to have
serious harmonic content with an almost complete wipeout of the 3875-3890
portion of that band.
I do not know if the building ground is even still properly connected
to a good earth point. It's not my building.
So, with this said I feel that there is the possibility that the
house earth conection is useless and would like to use a (clean) earth for
the entire station power along with some filtering as appropriate.
I have been in the live sound business for at least 30 years and
floating certain grounds for loop and noise elimination has often been
necessary but not really code.
Anyway, that is the story. A noise and safety issue rather than
Reply by Jim WD5JKO,
One other way to decouple the AC line to/from your ham equipment is to take a 25' extension cord (big heavy 12-3 cord) and make a common mode choke out of it l(spooled up with about a 1' diameter coil) like we often do to get common mode RF off of coax cable. This preserves the 3 wire system and is very safe. On HF, the choked cord does it's thing. You could add additional filtering to cut back on noise that occurs between the wires (mostly hot and neutral) by using conventional "differential mode" filters. Use the power from this cable to power up the shack. If you need 220v for an amplifier, do the same thing there also.
Then use a short beefy ground wire to a stout ground rod or cold water pipe. Depending on the distance you may also need some 1/4 long insulated ground wires in order to keep the station from being 'HoT'. The 16' ground wire mentioned earlier would make the station pretty hot on 20m, especially if the antenna used an unbalanced feed.
I like to convert my boat anchors to a 3 wire plug. Too many times I have disconnected a coax cable then be greeted by high AC voltage arm-to-arm. This usually happens when I am standing on a stool and leaning over. The 3 wire system eliminates these kinds of surprises...
Tracing down RFI sources can be a long and time consuming task. That said, you may be able to talk yourself into getting access to various things at your building. The clamp over ferrite beads can be slipped over wires pretty quickly and in the right areas can do a lot of good.
I'm no antenna expert but I think a closed loop antenna will give more satisfactory reception than a open ended dipole when the area near the antenna contains significant E-Field noise radiation..
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