Today's Message Index:
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1. 11:46 AM - Re: Re: Dipole antenna fabrication (Robert L. Nuckolls, III)
2. 12:57 PM - Re: Re: Dipole antenna fabrication (Jan de Jong)
Message 1
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| Subject: | Re: Dipole antenna fabrication |
Correction of typo . . .
> It took 0.2 to 0.33 uV (6 to 10 dB increase)
> to make that much difference.
Bob . . .
Message 2
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| Subject: | Re: Dipole antenna fabrication |
> I am glad to see others post good info. There are many Hams out there who are
quite skilled in this area. Thanks Jan de Jong. I'll be building one of those
for my Glastar's vertical stab.
>
I am thinking of building one of those for the Europa vertical stab as
well. The V-shape adjusts the impedance to 50 Ohms and improves
horizontal directivity . Whether it also increases bandwidth ("more
volume" - despite using cloth hanger wire?) I don't know.
Remarks:
- the lengths mentioned in the article may a little too great for
perfection when put inside a fiberglass structure, even when not touching
- the Pawsey stub could be tuned using a SWR meter and a dummy load
instead of the antenna; looking for largest possible SWR over the air
band; the transmitter used could be protected with a guaranteed load by
50 Ohm in-out voltage divider
- after that the antenna could be tuned looking for the smallest
possible SWR over the air band.
- if things are to be tuned anyway then the only concern in construction
is treating both legs of the dipole the same
I may instead go for the straight dipole as follows:
http://www.europa-aircraft.com/pdfs/buildersmanuals/CBM%20-%20ANNEX%20C.pdf
with the beads replaced by a (verified if not tuned) Pawsey stub, as
good enough.
As an added measure 2 choke baluns 1/4 wavelength apart anywhere on the
feedline would be effective.
I also found some literally orphaned DOS programs to play with:
http://www.zerobeat.net/G4FGQ/page3.html#S301%22
SOLNOID3 shows the effect of 4 turns of 5mm wire (coax) on 45mm former
(min. bending diameter) as a choke balun
LINELEN shows dipole performance in terms of losses, assuming a choke
balun. Amazingly the largest effect is the type of coax where I thought
RG58 would be good enough for my needs.
I think Bob is right - it's not all that critical. Good enough is not so
much worse than perfection.
I should get back to my regular program now from this interesting
diversion into radio.
Jan de Jong
* <http://www.zerobeat.net/G4FGQ/solnoid3.exe>*
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