Why would one feed a dipole, generally considered a balanced antenna, with
an unbalanced coax? Should you do so, then you do need a RF choke at the
feed point to reduce current on the outside of the shield. Oh there will
always be some due to the fact the coax is in the RF field generated by the
antenna and this is exacerbated by the fact that the coax feed line does not
exit the antenna perpendicular for at least 1/4 wavelength.
73
Bob, K4TAX
----- Original Message -----
From: "Gary Hoffman" <ghoffman@spacetech.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Saturday, April 04, 2009 5:13 PM
Subject: Re: [TenTec] RF Ground
>I don't feel that this is a particularly good example for the following
> reason.
>
> If, and only if, the ground point at the radio where the coax is
> terminated
> to the radio is an excellent RF ground, then any current flowing on the
> outside of the coax will be shunted to ground at that point. As it is an
> excellent ground, impedance is low, and voltage will thus be low as well
> .... ideally zero of course.
>
> Now I grant you that excellent RF grounds are extremely rare.
>
> I just don't think they are a BAD thing, in the event you are lucky enough
> to have one.
>
> I agree with other posters who have emphasised that lightning protection
> must be done OUTSIDE the shack. A different issue altogether.
>
> I also agree with other posters who have reiterated that ALL grounds must
> be
> bonded together....a requirement of both Code and safety, not to mention
> ground potential differences leading to annoying ground loops.
>
> As to Pin 1 problems, they exist sometimes. But remember there are many
> additional problems out there in the world. As the seer once said....if
> the
> only tool you have is a hammer, every problem looks like a nail. Keep a
> broad perspective on the potential sources of problems.
>
> 73 de Gary, AA2IZ
>
>
> ----- Original Message -----
> From: "Steve Hunt" <steve@karinya.net>
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Sent: Saturday, April 04, 2009 4:13 PM
> Subject: Re: [TenTec] RF Ground
>
>
>> Have you ever considered that providing a better local RF "ground" could
>> make "RF in the shack" problems worse?
>>
>> Take the example of a half-wave dipole fed with coax that is a multiple
>> of a half-wavelength long and bonded to a "good RF ground" at the shack
>> end. If there is no choke balun at the feedpoint, significant
>> common-mode current will flow down the outside of the coax braid because
>> it represents a low impedance path to earth. The better you make that
>> "RF ground", the higher the common-mode current and the greater the
>> potential for RF in the shack.
>>
>> Steve G3TXQ
>>
>> Martin Ewing wrote:
>>> Yes, but... It's still worth trying to establish a local RF "ground" --
>>> ensuring that everything in your shack is bonded together. No antenna
>>> system is perfect, and many of us have some RF in our shacks.
>>>
>>
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>>
>
>
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