[RFI] Shielding a ground wire

[Roger (K8RI)]

On 4/28/2013 2:42 PM, Roger (K8RI) wrote:
> On 4/28/2013 11:21 AM, Timo Toro wrote:
>> I did fix my problems already. My antenna systems are not incomplete. Of
>> course more and higher masts would be nice, hi.
>>
>> But if I run over 1KW to my 4el Yagi on 40m and my PC stops working, I
>> have to fix that problem. I did not use the band aid either. Nowadays my
>> ham shack is more like Faraday shield, hi. And lightning safe.

BTW I have two computer within 2 to 4 feet of the rigs in the shop.
I have a similar set up in the house/den  with a 5th computer in my 
wife's office, about 30 feet to the South of the ones in the Den.

The station in the house is an old Icom 756 Pro (Jim's favorite <:-)) ) 
driving an Alpha 76 while the one in the shop is a Yaesu FTDX5000MP 
driving an Emtron DX-2sp into a Palstar AT5K.

All 5 computers are wired to the stations and each other with CAT6 
through an 8 port switch. There are 3 runs of CAT6 and one phone line 
about 130 feet long between the house and shop. The towers and antennas 
for both stations are tied together with 32 or 33 8' ground rods, 
CadWelded(TM) to over 600 feet of bare #2 copper.

The tricky part is that the house and shop are on separate electrical 
feeds, but at least from the same transformer. There is close to 300 
feet of wire between them.  Actually my ground system ties both grounds 
together.

Even when I had 75 lighting up all the LEDs it did not bother the computers.

RF can get into the computer by direct pick up from the antennas, RF 
pick up via the house wiring, or common mode via the feed line. In some 
cases there is a phone line to the computer as well.

Depending on the age of the house, there may be some surprises on some 
circuits, but the most likely source is still common mode voltage 
on/from the feed line.

73

Roger (K8RI)

>
> Sounds like what I had on 75 with a center fed half wave, sloping, fan
> dipole. SWR  at resonance is less than 1.1 : 1.  When I'd get to around
> a KW out, all the LEDs on the control heads in the station would light.
> To me that said, RF on the feed line which meant it was on the ground as
> well.
>
> My first thought was a current balun.
> http://www.rogerhalstead.com/ham_files/AntennaFeed1.htm
> Not neat, but a very high impedance for common mod voltages.  It
> improved the situation but did not cure it, So I inserted another,
> similar choke where the feed line reached the tower and no more RF in
> the shack, feed lines, or ground.
>
> I stopped the RF at the source.
>
> An antenna may appear to have all its parts, a good SWR, and a good
> ground, but bear by objects, ground conditions under and near the
> antenna may leave you with an unbalanced system even though every thing
> looks good.  Matter of fact, it's extremely unlikely that an antenna
> will be truly balanced
>
> 73
>
> Roger (K8RI)
>
>>
>> I still like to use word "grounding" meaning low impedance route to
>> common point near earth potential.
>>
>> 73, Timo_oh5kw
>>
>>
>> At 9:08 -0700 28/4/13, Jim Brown wrote:
>>> On 4/28/2013 3:00 AM, Timo Toro wrote:
>>>> Tuning the ground lead to series resonance on most problematic band,
>>>> can help too. As was done in the example?, I sent earlier.
>>>
>>> This is NOT a solution, it is a "band aid."   The real CAUSES of the
>>> problems you are trying to solve are with improper or inadequate
>>> BONDING between equipment, and incomplete antenna systems.
>>>
>>> There is RF on that earth wire you are "tuning" because you are
>>> PUTTING the RF there. That wire is a conductor, so it is an ANTENNA,
>>> so it will radiate the current that you put on it and it will receive
>>> noise.  That earth wire is a problem either because your antenna
>>> systems are incomplete -- perhaps you have no counterpoise or radials
>>> on a long wire, for example, so return current for the antenna flows
>>> on that earth wire, so it is part of your antenna -- or because
>>> failure to bond together all equipment and all grounds causes current
>>> on that earth wire to couple into equipment.  To understand how this
>>> happens, study the tutorial material on "The Pin One Problem," on my
>>> website. http://k9yc.com/publish/htm  Almost all ham gear is built
>>> with Pin One Problems.
>>>
>>> 73, Jim K9YC.
>>> _______________________________________________
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>>> RFI at contesting.com
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>>
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