Topband: Shunt feeding AB-577/621

[k8gg at voyager.net]

Hi All,

A couple of thoughts:

I used an aluminum powder filled version of Permatex or similar anti-seize
compound the last time I put up an aluminum tower (Heights or Universal). 
No continuity problems.

Also with a rigid galvanized free-standing tower (Probably American Tower
or Pyrod) I used zinc filled anti-seize compound on the face of the
flanges between sections.  No conductivity problems for the 16 years it
was up with a shunt feed for 160 meters.

The AB-577 is probably resonant near 3.5 MHz with the C-3 antenna on top
if one wants to shunt feed it for 80 or 75 meters.

So, I vote for an inverted-L for 160 either supported from the top of the
mast or from a separate tree.

GL & 73,

George, K8GG


> Hi Pete,
>
> Good question. I haven't done it with any of my three AB-577s, but I've
> seen recommendations from others that the sections be electrically bonded.
>
> I'm not sure about the case for that. I just measured continuity on the
> flat portion of a spare tube and it showed zero ohms. If the contact areas
> are clean when the mast is assembled, they should make good contact with
> zero resistance. The clamp should act to keep the flat areas in contact,
> as should the downward pressure from the guys. I guess it may be possible
> that dirt carried by rain water might seep into the clamp and get between
> the sections as they rock back and forth in the wind, even if it's just by
> nanometers.
>
> If you buy that possibility, I think it can be overcome pretty easily by
> attaching right-angle tabs to the top and bottom of each section with
> screws/nuts, and running a section of copper strap between them, also
> secured with screws and nuts, or perhaps you can find some sort of clamp
> that would let you quickly connect/disconnect the strap as you raise/lower
> the mast.
>
> Hope this helps.
>
> 73, Dick WC1M
>
> -----Original Message-----
> From: N4ZR <n4zr at comcast.net>
> Sent: Monday, October 1, 2018 11:48 AM
> To: topband reflector <Topband at contesting.com>
> Subject: Topband: Shunt feeding AB-577/621
>
> I have an AB-577 with a C-3E on top, and am interested in the possibility
> of shunt-feeding it for 160 - 100 watts only.  Anyone have any experience
> with doing this?  Are the section-to-section joints adequately conductive?
>  I would plan to use an omega match, because I'm guessing it would be well
> short of a quarter wave.
>
> My other option is an inverted L.  Should I maybe just go ahead with that?
>
> --
>
> 73, Pete N4ZR
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