Posted by
G3VVT on
Jan 30, 2005; 1:01am
URL: http://elecraft.85.s1.nabble.com/Elecraft-RFI-Problems-tp374033p374037.html
In a message dated 29/01/05 16:36:57 GMT Standard Time,
[hidden email]
writes:
If you have a balanced antenna
system, or even an unbalanced system with RF properly choked off from the
outside of your coax, there will be no RF on the chassis that 'as to go
somewhere'.
In addition, it is very difficult to provide an RF ground at HF.
---------------------------------------------------------
With my shack in an upstairs spare bedroom it is difficult to provide an RF
ground in any case, the only ground being the power ground. The house is
built on rock so I doubt if a ground rod would go in very deep even if I tried.
Opted like Vic for a balanced antenna with balanced feeder. Using 100W have
not seen any problems unless I try to operate on a band that the antenna is
not resonant on. Using 75 ohm balanced twin as the feeder as the use of 300 ohm
ribbon or higher would be impractical from my shack. The 75 ohm twin seems
quite docile in use and can be installed in close proximity to metallic
objects which is not recommended for 300 ohm or higher impedance twin feeder.
To date the only interference problem have been with telephones whose drop
wires are parallel to my antenna. The phone company fitted RF filters to the
affected telephones at the point of entry into the house and one modern
telephone had to be suppressed internally. Older telephones seem less affected. A
problem that may be coming up is the use of ADSL broadband would probably
prevent normal telephone RF suppressers being used at the point of entry to the
house as this would also stop ADSL from working. A separate RF filter at each
telephone would be the only answer in this case.
As a parallel subject there was an interesting article in the February 2005
Radcom, EMC column advocating the use of ADSL telephone filters as being very
suitable for use as RF filters on telephones for the lower bands and the
performance figures for one type of ADSL filter were quoted. See them available
at computer fairs at about £3 each ($5.70 US).
Bob, G3VVT
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