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adding coax lowers SWR reading on the meter?

mr_fx said:
I had not even thought about that... now that you mention it, the 8 foot pole would not be enough would it...
Click to expand...

Don't think 20' would do it if the coax doesn't, not sure the base is connected to anything other than the coaxes shield which makes it the counterpoise.
 
mackmobile43 said:
Don't think 20' would do it if the coax doesn't, not sure the base is connected to anything other than the coaxes shield which makes it the counterpoise.
Click to expand...

I could test it by connecting a wire to the base of the mast...

OR I could isolate the mast from the antenna and connect the GPK... BUT it is missing 2 radial... I could just make those out of wire... so 2 would be wire and the other 2 would be OEM

OR... I could just isolate the mast and the antenna and use 4 69-72" long pieces of wire and form a new and CHEAP GPK
 
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mr_fx said:
I could test it by connecting a wire to the base of the mast...

OR I could isolate the mast from the antenna and connect the GPK... BUT it is missing 2 radial... I could just make those out of wire... so 2 would be wire and the other 2 would be OEM

OR... I could just isolate the mast and the antenna and use 4 69-72" long pieces of wire and form a new and CHEAP GPK
Click to expand...

yes
 
the a99 is a 1/2 wave so you only need about 24 inches of radial. if you can fabrickate a hub try using about 10-20 24 inch radials (like the kit he used in this video) just below the rings conected to the aluminum mounting tube to decouple the coax then retune it untuil your swrs are flat

http://www.youtube.com/watch?v=ueg_n57J_XU )
 
mr_fx said:
I could test it by connecting a wire to the base of the mast...

OR I could isolate the mast from the antenna and connect the GPK... BUT it is missing 2 radial... I could just make those out of wire... so 2 would be wire and the other 2 would be OEM

OR... I could just isolate the mast and the antenna and use 4 69-72" long pieces of wire and form a new and CHEAP GPK
Click to expand...

You can use four guy wires cut to the same length as the GPK length for the ground planes and attach them to the antenna at the base of the tuning rings. Then at the other end of the wires attach them to dacron rope and use that to secure it to the building 90 degrees apart from each other. You will also need to keep the angle of these ground planes wires at/around 40/50 degrees relative to the Earth and re-tune the antennas tuning rings for the lowest SWR. That should work just fine. Just make sure you measure twice and cut once for the ground plane lengths.

It isn't necessary to insulate the antenna from the mast; but it won't hurt either.
 

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Needle Bender said:
the a99 is a 1/2 wave so you only need about 24 inches of radial. if you can fabrickate a hub try using about 10-20 24 inch radials (like the kit he used in this video) just below the rings conected to the aluminum mounting tube to decouple the coax then retune it untuil your swrs are flat
Click to expand...


10-20 radials at 24"

really? I was thinking about connecting multiple radials with wire, kind of like a web?
 
mr_fx said:
well the 4.25" 5 turn choke did the trick... max SWR is now 1.25 in the CB band and it stays under 1.7 a band up and a band down
Click to expand...


déjà vu

to change vswr you must change the load,

walt maxwell REFLECTIONS 2, chapter 2 ( countdown for a journey from mythology to reality )
sec 2.3 ( true or false ) 21) 22) 23)

and REFLECTIONS 2, chapter 21 ( some aspects of the balun problem )
sec 21.3 ( should SWR change with line length )


index
 
the REASON your VSWR changes when you add/remove coax (assuming there are no other coax issues) is because your antenna is not a pure resistive load.


btw,... an antennas lowest VSWR freq and the antennas resonance freq may not be the same:pop:
 
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"... an antennas lowest VSWR freq and the antennas resonance freq may not be the same"

And to add just a tiny bit more to that... there are very few times when any antenna's input impedance is ever 50 ohms, or even 'close'. If it is, and if some kind of impedance matching device isn't used, then hang onto that thing 'cuz' it's a miracle! :)
- 'Doc
 
Needle Bender said:
the a99 is a 1/2 wave so you only need about 24 inches of radial. if you can fabrickate a hub try using about 10-20 24 inch radials (like the kit he used in this video) just below the rings conected to the aluminum mounting tube to decouple the coax then retune it untuil your swrs are flat

Boomer Ground Radial Kit fitted on a Shakesphere Army Big Stick CB Radio antenna. - YouTube )
Click to expand...

NB, I'm not too sure about your claim above. I am working on a similar set of models using an end fed 1/2 wave, but here are three models with the .625 wave radiator like Dave is using.

Here is a model using 8 x 1/4 wave radials on a non-isolated mast compared to an antenna like Dave is using with 8 x 24" radials on a non-isolated mast. The two models with 24" radials have the radials set at the bottom of the antenna mount for one vs. the top of the mount for the other. Take note of the current flow (red) in the mast area of these models, and I think you might see why full length radials are preferable. The gain for these antennas is not a big issue, but check the pattern affects for the high angle lobes for each antenna...and I think you'll see where the radial length might make a difference if your concerns are for possible CMC affects.

View attachment NB's .625w idea for more radials..pdf
 
i had better results with 1/4 WL ground elements than more shorter ones . hey marconi , can you model a 1/4 WGP with four sloped 1/4 wl ground elements vs. four sloped 1/2 wl ground elements on the CB band ? can you also do the same with a 5/8 wgp ?

thanks :)
 

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