[TowerTalk] Dipole Problem

[David Robbins K1TTT]

Its probably not the egg.  I would bet there is an interaction with
something in or under the roof, wiring, gutters, drip edge, flashing,
etc. also bending the ends will change it a bit.  Remember also that the
lower to the ground a dipole is the lower the impedance, so you may not
be too far off anyway.  

A 2:1 balun would bring you right up to 50 ohms or so.  With just about
any feedline of reasonable length the loss on 75m would be negligible so
you could feed it directly and just put a tuner in the shack, which
would also give added flexibility for tuning other places in the band or
even for other bands.


David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of K6TFZ at aol.com
> Sent: Wednesday, February 18, 2004 22:18
> To: towertalk at contesting.com
> Subject: [TowerTalk] Dipole Problem
> 
> I always thought a dipole was simple. First the description:
> 
> 75 meter dipole (58.5 feet per leg) placed 4 feet above peak of second
> story
> roof. Roof is 40 feet wide so ran extra wire at right angle outward
toward
> rest of house (big square "U").
> Center of dipole is in center of 40 foot section using a large egg
> insulator
> and an SO-239
> to start, balun later.
> 
> My AEA-HF and Autek RF-1 both read resonance at 3968 KHz which is fine
BUT
> SWR is about 2.3:1, R=29 ohms.
> 
> The only thing I can figure is the way I wrapped the wire on the egg
> insulator: so that if
> the insulator were to break, the wires would catch each other and not
> part.
> 
> Could there be that much capacitance there to throw my reading off
that
> much?
> The wires are at right angles to each other. Any other suggestions?
> 
> TIA.  Geoff, K6TFZ
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