Since I have (now had) a linear loaded 160m vertical I
wanted to try to measure if that loading gave any loss.
So here goes:
Case: 100ft vertical with linear loading 26ft up and down,
resonant at 1890 kHz with 32 ohms measured with MFJ269.
Tuner at the base with edge-wound roller coil etc to
tune it to 1830.
For signal source antenna a 80m vertical was used standing
about 450 feet away.
Measure equipment: HP 8591E and 8640B
Result: 0.5 dB loss due to liner loading, result could be
repeated time after time.
Bottom line: Thank you W8JI for the 0.5 dB gain.
Linear loading is now removed permanently!
73 Jim SM2EKM
----------------------------------------------------------
Tom Rauch wrote:
>>loading a wire antenna.
>
>
> I'd be careful about that. Linear loading has very low Q.
> You can think of linear loading a very poor form factor
> loading coil.
>
> Assume we have a coil that uses five feet of #16 wire in an
> air wound coil. We probably have a Q of around 200 or 300.
> With 250 ohms reactance the series loss resistance would be
> only around 1 ohm.
>
> Using a folded stub of air insulated #16 wire, Q is
> typically around 25 to 50. We would have about five to ten
> ohms of loss resistance.
>
> The thing that kills Q of a folded wire stub (linear
> loading) is the stray capacitance between the conductors and
> the fact overall wire length has to be significantly longer
> for the same reactance. It's actually just like we took a
> good high Q coil and stretched it out into a long single
> turn, ruining the form factor. Adding a dielectric only
> makes it worse because it increases the shunt capacitance.
>
> 73 Tom
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