Hi Jim:
You may just be right about other things in the house generating RFI,
however, a grand majority of my problem went away by just turning the
computer off. This being the case, proximity to the antenna coax to the
computer is the big problem. Short of doing away with the computer (not
an option), I agree with Ian that the coax shield is primarily picking
this up. His point was that this energy goes retrograde up to the
antenna and then sends it back down the center conductor. I believe
this energy goes both retrograde and antegrade, as I did notice
decreased intensity of the interference by adding a 'line isolator' (a
current balun by Antenna Works) at the antenna switch. This did allow
signals to be heard which could not be heard before, so I don't think
I'm adding loss there, just choking the antegrade interference. But
your point is well taken as I have noticed that when I approach the
house listening to AM in my truck, there is much signal loss and
interference.
Jamie
WB4YDL
On Sunday, August 4, 2002, at 03:24 PM, Jim Lawler / WY0B wrote:
> Hi Jamie,
>
> It sounds to me like you have some RFI generated in your house.
>
> Before I tried extra coax, (can't imagine that would help much, except
> for
> the additional loss the extra coax would cause to all received signals,
> including to the signal you want to receive), I would trip all breakers
> in
> your house one at a time and see if the RFI clears when a particular
> breaker
> is tripped. Then, inspect / turn off ALL devices on that circuit.
>
> Just my .01 cent worth (figuring in inflation, of course.)
>
> 73,
> Jim / WY0B ...
>
> ----- Original Message -----
> From: "James C. Hall, MD" <nwtncc@iswt.com>
> To: <rfi@contesting.com>
> Sent: Saturday, August 03, 2002 5:28 PM
> Subject: [RFI] Computer RFI problem
>
>
>> Here is an interesting problem:
>>
>> I put up an old Cushcraft R-7000 on the roof as a secondary antenna. My
>> primary antennae are on a tower 150 feet from the shack and perform
>> very
>> well without RFI difficulties. When receiving with the vertical on 20
>> meters, I hear S9 computer generated interference. Changing antennas to
>> either the beam or an inverted V yields no such interference. This only
>> occurs on 20 meters - at least very audibly - and only with the
>> vertical.
> I
>> used to have trouble with the lower frequency bands ie. 75/80 meters
>> until
> I
>> switched out the computer power supply with a better filtered and
>> shielded
>> one. Now no problem on those bands.
>>
>> I'm thinking about adding some length to the coax off the vertical to
>> see
> if
>> that would help ... but I doubt it.
>>
>> Any ideas ?
>>
>> Thanks,
>>
>> Jamie
>> WB4YDL
>>
>>
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>
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