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32 FT VERTICAL -- counterpoise length??



 
 
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  #1  
Old August 20th 03, 06:46 AM
VE8AE Andrew
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Default 32 FT VERTICAL -- counterpoise length??

I have an old Shakespear 32 ft antenna. Fed at side near bottom and a
large bottom plate. Want to know if I mount it up at the top of a mast
how long should I make radial wires for? Do I just calculate for
lowest freq and make them 1/8 wavelength? I am going to run it through
my tuner to get as many bands out of it as I can. Only about 40ft of
coax so it is not too long.
Or should I try and design my own trap vertical of some sort??
Thanks.
Andrew VE8AE
  #2  
Old August 20th 03, 07:16 PM
Mark Keith
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(VE8AE Andrew) wrote in message . com...
I have an old Shakespear 32 ft antenna. Fed at side near bottom and a
large bottom plate. Want to know if I mount it up at the top of a mast
how long should I make radial wires for? Do I just calculate for
lowest freq and make them 1/8 wavelength? I am going to run it through
my tuner to get as many bands out of it as I can. Only about 40ft of
coax so it is not too long.
Or should I try and design my own trap vertical of some sort??
Thanks.
Andrew VE8AE


I assume it's an unloaded fiberglass whip....Perfect for a 40m
antenna. If elevated, use 1/4 wave radials "appx 32-33 ft". Trim for
best match. You could feed it as a 5/8 on 17m with a small series
loading coil at the base. It should work ok on 15m, if you use the
tuner. The other bands, the feedline and tuner losses will vary. Just
try it and see. For any certain band used, you would prefer at least
one or more 1/4 wave radial. But 3/4 wave radials can work also. So
40m radials can double for 17 and 15 with decent results. If you try
to use with a tuner on bands where the match is lousy, I would prefer
a thicker low loss coax. So I would use rg-8/213, etc instead of
rg-58. Matched, the differece is very small, but I think it can
noticeably reduce losses a bit when you have a big mismatch. The
higher the freq, the more you would notice the difference. On the low
bands, it would hardly matter. You could feed it as a 1/2 wave on 20m
with very good results, IE: gamma loop feed, but that matching scheme
is going to be quite different than a 40/17 antenna. If you do this,
consider it a single band antenna for the most part. You would need to
pick one or the other. Hard to do all at the same time. Maybe use a
autotuner...But autotuners seem to be sort of lossy in such cases.
Also, if you use a loading coil, say for 17m use, it's best not to
ground the base. Just run it in series. You don't really want to dc
ground an antenna you are trying to run on all bands with a tuner, or
even dual band like the 40/17 combo. If you ground the coil, it will
ruin it on 40m. If you don't ground the coil, it just drops the
resonant freq on 40m a bit. I used a 24 volt relay to switch on one I
ran. MK
  #4  
Old August 21st 03, 02:42 AM
'Doc
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Bill,
'Cuz people don't want to build an antenna.
'Doc
  #5  
Old August 21st 03, 02:45 PM
Mark Keith
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Richard Clark wrote in message

Use a tuner and forget tuning the radials. You might be tempted to
build them to "formula" but given that they will no doubt be of the
drooping variety, then that is an entirely different game. As such,
add as many as you are comfortable with, as long as you can make them
without having to bury their tips (a good idea is that their lowest
point should be out of reach).


Myself, I would tune them, or have them very close. Or at least on the
preferred band. Better decoupling from the feedline for one thing. If
the radials do not present a low Z for a certain band, they won't work
too well at all. I would grount mount if I didn't want to tune the
radials. It's going to be very hard to get proper performance on all
bands with only one tuning setup, unless maybe he uses an autotuner of
some type. "elevated"
I'd pick the most likely used bands and build for those. IE: it will
be hard to run 40 and 20 both, with good results on both bands. If I
ran 40/17m as the main design, I'd forget about 20m. And visa versa.
If not, be prepared for mediocre results on one of the bands. I've
never tried feeding an elevated GP/non resonant radials with ladder
line and a tuner. I know it can be done, but I wonder about the amount
of common mode currents and performance on "non radialed" bands,
compared to a normal setup with 1/4 wave radials.

Be aware that as impressive as it may feel, the height may be a
detriment in the higher HF (too long and radiation will be skyward,
bound).


Not the height, but the length of the antenna is too tall for the
higher HF bands for good low angle performance. IE: 10-12 meters. It
will be ok 15m down.
This is probably what you meant...
MK
  #6  
Old August 22nd 03, 03:36 AM
K9SQG
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Ideally the counterpoise should have 3-4 radials per band, sloping down at
about a 30-45 deg angle.
 




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