[TowerTalk] Shunt Feed

[dan hearn]

Sounds like you may have BC station pickup on the tower. Try your
exciter on low power and I bet it works OK;. 73, Dan, N5AR

Pete Smith wrote:
> 
> My education has just been found wanting again.  I'm trying to set up a
> shunt feed for my tower for 160m.  After tapping up the tower about 30
> feet, I set up a test rig at the feedpoint to let me clip-lead in various
> values of low-voltage ceramic caps in series with the shunt lead, to tune
> out the presumed inductive reactance.  As I added capacitance to the series
> cap in the shunt feed and measured the Z, I could see it come down as I
> added more C -- in other words, it behaved as I expected.  I found that
> with 440 pf in series, my Autek RF-1 says that minimum Z occurs at 47 ohms
> at 1895 khz.  It is a relatively sharp minimum.
> 
> Yet when I switch the meter to SWR, it says it is off-scale high.
> Is this possible?  Doesn't minimum Z (R+j0)represent resonance?  And if
> that minimum number is ~50 ohms, shouldn't the SWR be somewhere under 2:1.?
> The meter reads all right on other antennas for other frequencies, and with
> a 50-ohm resistor across the coax connector it reads close to 1:1 SWR at
> 1.8 MHz.
> 
> There must be something here I don't understand.  Any help gratefully
> received.
> 
> 73, Pete N4ZR
> 
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List Sponsored by AN Wireless:  AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!!  http://www.anwireless.com

-----
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