Topband: Interesting Observation

[cris blak]

Hi Ed,

I use an INV-L with 36 short suspended radials. I check the resonance and its impedance using I-V method with current transformer and an oscilloscope.

For ground system I use also a 1.5m copper electrode. Using I-V method, without radials, only the copper electrode, I measured about 41 ohm. With all 36 radials I have about 33ohm. In between there is a peak of 56ohm with 8 radials than the impedance decrease to 33ohm.
With less than 16 radials, the resonance frequency vary with the soil characteristic. When the soil is wet, the resonance frequency decreasing  (conductivity is increasing). With 36 radials, the resonance frequency variation is much less. The soil surface coverage with 36 radials is about 70% (in my case).

My guess is that your problem is due to poor ground system and due to ground conductivity variation and less due to leaves.

To optimize the ground system quality, increase the ground coverage with radials as much as the impedance decrease will stop or vary a little.

For impedance measurement I don't recommend gears like miniVNA, MFJ2xx but N2PK VNA or, as simple as I-V method. This way, one will be sure about what he/she is doing!

Good luck,

73 de YO3FFF
Cristi 



----- Original Message ----
From: Edward Swynar <gswynar at durham.net>
To: topband at contesting.com
Sent: Wed, February 3, 2010 8:11:18 PM
Subject: Topband: Interesting Observation


Lo & behold, each "L" now tunes to 1914-KHz, +/- 2-KHz---an upward increase
of some 44-KHz!

Whether this is because of the fact that the ground beneath the radial field
is now frozen, or because there are no leaves in the trees supporting the
elements (or sap flowing through the trunks & branches of same), is
unknown...but it IS interesting to note that the upward changes in resonant
frequencies were surprisingly in sync with one another.

Perhaps this might, indirectly, help explain why some antennas have
"...suddenly changed SWR" inexplicably in the past month or so, as more than
one topbander has told me...

~73~ de Eddy VE3CUI - VE3XZ


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