I did some topband operating in the CQ WW 160 contest this past weekend courtesy
of an invite from Paul, N6LL to his sight on Mt Wilson, Ca. The sight which
overlooks the
L.A. Basin, consists of several slopers hung off a 270' tower and a number of
beverages
which were erected by one of Paul's colleagues who works with him at the site.
Although
the site is very quite relative to the buzz of the city, I am beginning to
suspect that the beverages
could stand to be improved.
I still don't have a complete picture of how and where all the beverages at the
site are situated,
but I was able to explore the site a little with Paul on Saturday afternoon at
which time I was
able to find and follow several of the beverage wires. Additionally, Paul and I
were able to repair
the northeast and east wires which previously hadn't been working. Although it
was a good feeling
to have a couple more antennas to choose from, I found strangely enough, that
only three of the
half dozen receive antennas at the site seemed to work effectively. On Friday
night the beverage
labelled NE/SW seemed to provide the best signal/noise for most of the signals
I was trying to
copy. Aside from the label on the switchbox, I have no clue as to how long this
antenna is, how
its fed or terminated, or even what direction it actually runs. Oddly enough it
seemed to work
equally well (or equally poorly perhaps) to both the east coast, the carribean,
and JA. The beverage
labelled NW did work better to the northwestern US and Canada and Alaska, but
was less effective
than the NE/SW antenna to JA. On Saturday night the North antenna seemed to
outperform the
NE/SW antenna to the east coast, but the NE/SW antenna still excelled toward
JA. On Saturday night,
the trasmit antenna provided the best signal to noise while I was listening to
YV5JDP. Needless to say,
I was a little perplexed and disapointed with the beverages.
At any rate, either we were experiencing some very strange skew path
propagation, or these beverages
weren't really working properly. One thought that came to mind was the close
proximity of the 1000'
TV trasmitting tower present at the site with its long conductive guys. In fact
two of the beverages (the north
and east I believe) are fed from the northwest guy pier of the tower (they
share their ground connection
with the pier's ground). Does anyone have a good feel for how much interaction
their would be between these
beverages and the tower guys? Or how far away they would need to be to achieve
good performance (clean
pattern, good F/B). The other question I have is what effect will the irregular
mountain terrain have on the
beverage performance. Seems that this might cause the characteristic Z of the
beverage to vary considerably
which might in turn make it hard to achieve a good F/B ratio (due to structural
reflections). Anyone have any
thoughts on this?
This is really a great site, and if possible I would like to invest some time
in improving these receive antennas
(proper terminations and matching), but if the big tower guys can't be
effectively decoupled, it might not be
possible to ever get them to work really well. If this is the case, perhaps I
might be better off to investigate
alternative receive antennas (probe arrays, EWE's, etc).
Thanks,
Mike, W4EF (opr W6UE/p Mt Wilson, Ca)
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