Hi Ed,
My 160 meter 4-square array uses two 125 foot towers and two vertical wires
suspended from catenaries. When I initially tuned the array I discovered that
the resonant frequency of the wire elements varies in proportion to the tension
applied to the wires. When the tension is reduced -- even slightly -- the
overall height of the vertical is reduced and the resonant frequency goes up.
When the tension is increased, the top of wire vertical approaches it maximum
possible height (without breaking or stretching the wire...) and the resonant
frequency goes down.
73
Frank
W3LPL
>---- Original message ----
>>Date: Wed, 3 Feb 2010 13:11:18 -0500
>>From: "Edward Swynar" <gswynar@durham.net>
>>Subject: Topband: Interesting Observation
>>To: <topband@contesting.com>
>>
>>Hi Guys,
>>
>>I don't really know what the significance of this might be, as in all
>>honesty I never really had any reason to do this before...
>>
>>In any event, here's the "interesting observation" alluded to in the title:
>>last October, when the outside air temperature here hovered around the 60's
>>F mark (it seems so very long ago that I can scarcely remember!), I set-up
>>the three inverted "L" elements in my array to each resonate within 1-KHz or
>>two, of each other, spot-on 1870-KHz (don't ask why I chose that
>>frequency---it's a L-O-N-G story, for some other time).
>>
>>Yesterday I had issues with the rotary direction switch used here that I had
>>initially thought was a problem with the resonance shifting, for reason(s)
>>unknown, on one of the "L's"...so I repeated a check of the individual
>>resonance of each element again, but with the ambient air temperature now
>>hovering in the typical January low 20's F.
>>
>>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
>>
>>
>>_______________________________________________
>>UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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