[amsat-bb] When exactly is a non-conductive mast necessary?

[Ev Tupis]

 You've received some excellent information with that link to Kent's articles.

In regard to coax selection (not what you asked about, but some input you received), "better is always better", but the question becomes, "How much better?"
The answer is in the math.
If running the FM satellites from an HT and your coax is 3' from HT to antenna, using RG8x will result in 0.3 dB of attenuation at 70cm.  Using LMR-400 will be "better" at "only" 0.1 dB.  In the real world, the 0.2 dB difference is indistinguishable.

My point is not to contradict John's statement.  It is to add perspective and a pathway to allow you to decide what is best for your usage.
Cheers,Ev, W2EV
https://www.timesmicrowave.com/Calculator




    On Monday, December 30, 2019, 9:26:47 PM EST, John Kludt via AMSAT-BB <amsat-bb at amsat.org> wrote:  
 
 Cathryn,

And if you pay attention to all of the caveats in his paper.  One saving
grace about all of this is it is not EME.  If you were working with
250 +/-  dB path loss and a passive reflector like the moon you might come
to a different conclusion.  Just be careful of all of the those 1/2
wavelengths and 1 wavelengths that he speaks about.  Especially for the 70
cm uplinks as that isn't very many inches.

The other thing I have seen folks trip over is coax selection.  Satellites
are not the place to be using RG-8X.  Others may have other thoughts I
think you are looking at LMR400 or its equivalent or better if it is a
permanent installation.

John


On Mon, Dec 30, 2019 at 7:57 PM Cathryn Mataga via AMSAT-BB <
amsat-bb at amsat.org> wrote:

> Oh, thanks guys. This is eye-opening.  It looks like even circular
> polarized antennas will work with metal masts, if you rotate them 45
> degrees.
>
>
> On 12/30/2019 2:31 PM, Gary wrote:
> > The short answer is almost never. Here is a link to an AMSAT Symposium
> paper form antenna guru Kent Britain, wa5vjb (inventor of the famous cheap
> yagis). He actually measured the effects.
> > http://www.kk0sd.net/metalboom/metalboom.htm
> >
> >
> > 73,
> > Joe kk0sd
> >
> >
> > -----Original Message-----
> > From: AMSAT-BB <amsat-bb-bounces at amsat.org> On Behalf Of Cathryn Mataga
> via AMSAT-BB
> > Sent: Monday, December 30, 2019 3:27 PM
> > To: amsat-bb at amsat.org
> > Subject: [amsat-bb] When exactly is a non-conductive mast necessary?
> >
> > I'm trying to understand, under what circumstances is a non-conductive
> mast necessary at VHF/UHF frequencies. Thinking of the following installs.
> >
> > 1.  Circular polarized antenna mounted to the mast at the center of the
> boom.    This is clear, see this advice all the time, fiberglass mast.
> >
> > 2. Same antenna but mounted at the rear end of the boom.
> >
> > 3.  Vertical Yagi, elements parallel to a vertical mast, mounted at the
> center of the boom. I guess, non-conductive wold be required here.
> >
> > 4.  Same antenna but rear mounted.
> >
> > 5.  Horizontal Yagi, elements perpendicular to a vertical mast, mounted
> at the center of the boom.  I think this is pretty normal install, so a
> conductive mast would be okay?
> >
> > 6. Same antenna but mounted at the rear of the boom.
> >
> > _______________________________________________
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Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
to all interested persons worldwide without requiring membership. Opinions expressed
are solely those of the author, and do not reflect the official views of AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
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