Bob:
There have been postings here on TT about the correction factor required
for dipoles when constructed with insulated wire. Most sources showed a 3-5%
shortening when PVC insulated wire was used. That is in the ballpark of your
cited figure, below. (The 'Skins are playing right now, otherwise I'd spend a
bit more time looking for the prior postings.)
73 de
Gene Smar AD3F
<The difference between theory and practice in theory is less than the
difference between theory and practice in practice.>
> I slapped together an 80m dipole using the L=468/F formula and find that it
> resonates about 200 KHz lower than expected.
>
> My target frequency was 3.775 MHz. That's 124 feet on my calculator.
>
> I built it using some left-over solid copper 12 gauge plastic jacketed house
> wire. I center feed it with 100' of RG-59/a coax. One end is up 60 feet, the
> other end about 40 feet. Using my AEA HF Analyst, it dips at 3.585 MHz with a
> VSWR of 1.6:1. This is a 5.3% difference in length from the formula.
>
> I can easily trim the length to meet my design goal, but I am curious why
> theory
> doesn't match reality a little closer. Does the plastic jacket affect the
> length? I would expect the resonant point to drop somewhat if the antenna was
> "dragging on the ground". Or is 50' of height not adequate?
>
> Thanks for any insight!
>
> 73 de Bob - K0RC
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather
> Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
> and ask for Sherman, W2FLA.
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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