I *very much* appreciate the many replies to my post. I've known about the
effect of foliage at VHF and above for a long time, but I think I've just
learned something new and useful. :-)
Since the vertical portion of my inverted-L is over 10 feet from the tall
oak tree (and its leafy branches) that supports it, I didn't think it could
be the reason for the poor signal reports and low signal levels on the
Reverse Beacon Network lately. However, the inverted-L and radials
--including the high voltage points-- most certainly are surrounded with
foliage. The rain here this spring and summer has caused an explosive
growth, not only of the leaves on the many oak trees that surround the area
where the inverted L is located, but also the weeds in that area! Many
weeds are at least 8 feet high, and not that far below the ends of the 10'
high radials and the end of the sloping L portion. Since I can't easily get
to the ends of the radials and antenna right now, I can't say for sure how
far below the HV points the weeds are.
In any case, the resonant point has not moved much since early spring, FWIW.
There's too many weeds, ticks and chiggers back by the antenna to do much
about it right now. But I can see that there may very well be a real change
for the better if I move the antenna to another area here, that I can mow
with the equipment that I have.
Someday, I'd love to do a better, long-term test comparing a separate
vertical in the middle of the pasture away from all the foliage. But there
never seems to be enough $ for a tower (among the other things that have to
happen in order for the tower to be erected) here.
I got the OK from John to post his e-mail to me (below) here, sent off the
reflector. It's interesting that this effect seems to increase as we go
down in frequency.
73, Mike
www,w0btu.com
On Thu, Aug 1, 2013 at 10:00 PM, John Langridge <jlangridge@sbcglobal.net>
wrote:
>
> Mike,
>
> Its been a few years since I have "seriously" spent every waking dark
moment in the seat on 80 or 160 so let me relate the behavior discussed to
even lower freqs.
>
> I've been an independent Part 5 operator on 630m now for almost a year.
I live in an area with deciduous cedar/juniper and have a lot of foliage
on my property around my antenna, a 72 foot T-top vertical with a natural
resonance near 1830 KHz and 130, 100-foot radials.
>
> My impressions on 630 meters after this spring and summer seem to be in
line with the figure relating freq and loss due to foliage. In short,
relative FS measurements made during the winter and spring/summer seem to
suggest a very significant amount of loss during the summer, in many cases
10-15 db decreases in relative signal strength. One can make the statement
that its dry and impacting ground conditions at those freqs more than say
at 80 or 160m due to the sheer scaling of the radial field but we have had
an uncharacteristically wet summer and quite good ground conditions
regionally. Note the measurements are totally unscientific and not done on
calibrated commercial gear. There is lots of wiggle room on the values,
but we are in the ballpark. As expected, both groundwave and skywave paths
have been severely impacted and confirmed by measurements using WSPR (a
decent "relative" method, I suppose) during relatively quiet conditions.
>
> As the figure mentioned earlier suggests, it appears to really scale
with freq and its been very obvious below the BC band... I never considered
it too much when active on 80 or 160 but I have learned that when the sap
flows in those cedar trees is very important and seems to correlate with
the times of poorest performance on 630m. I also note a significant shift
in feedpoint impedance between winter and summer so there is definitely
some impact not associated with ground conditions.
>
> I am not adequately treating this discussion as its late and I am tired
but that is my experience on even lower bands and there is an exponential
relationship for sure. Whether it can be realistically perceived on 80 or
160 is another story.
>
> Im interested to hear what other say. Thanks for bringing this up.
>
> 73,
>
> John KB5NJD/WG2XIQ
_________________
Topband Reflector
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