In a message dated 2/5/99 2:54:30 AM Eastern Standard Time, W4EF@pacbell.net
writes:
<< 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. >>
Mike and other antenna aficionados:
Back in 80s, I (VE3BMV) operated 160m contests from an FM TX site with 350 ft
tower, had slopers and beverages. QTH was on a hill with gradual slopes in all
directions. I put up "killer" 1600 ft beverages running down the slopes. First
night it was disappointment. Slopers and Inv. Vee beat the beverages. I
figured that length and terrain slope is making them too low angle. For the
next night I cut them in half, pull them in (got more directions) and the
difference was day and night. They worked like they supposed to. So the
conclusion was that having beverages more than abt 800 ft on a sloping terrain
is no good. (I don't have "scientific" study, nor white coat, nor I have
written paper on this to scientific publication.) (Disclaimer for "experts" in
white coats and antenna simulation software.)
<< 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
labeled 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. >>
The first rule, before the contest is to inspect your beverages (and other
antennas), they could be torn, eaten, fallen, etc. You should check the
termination, matchboxes, connections, cable continuity. They could be blown or
fried by lightning or pests. You should know their length, that would give you
some idea of expected performance.
<<Oddly enough it seemed to work
equally well (or equally poorly perhaps) to both the East coast, the
Caribbean, and JA. The beverage
labeled 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 transmit antenna provided the best signal to noise
while I was listening to YV5JDP. Needless to say, I was a little perplexed and
disappointed with the beverages.
At any rate, either we were experiencing some very strange skew path
propagation, or these beverages weren't really working properly. >>
It is nothing strange with skewed, gray line or long path propagation on 160m.
The more and better antennas you have (more you can see), you will find that
anything could happen, including dusting, selective ducting and varying
angles. 160m is on the borderline of LW/MW and SW bands and can exhibit weird
combination of modes, angles, directions. Even low 30 ft high inverted Vee can
sometimes outdo the rest of the arsenal. (had that happen with A45 and T32,
ONLY low inverted Vee heard them, none of the 12 beverages or 4 square at
VE1ZZ could!!!).
Welcome to "high performance" 160 operating!!
<<One thought that came to mind was the close proximity of the 1000'
TV transmitting 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? >>
Most likely interaction happens when there are resonant lengths of wires or
antennas around. Random size metal objects can work as reflectors and create
some RF hot spots or "black holes" "sucking" (canceling) signals.
<< 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). >>
Based on my experience in similar situation, I would say first get the
beverages going. Cut them no more than 800 ft. Make sure termination is right.
Others described proper way of finding right resistors. I used antenna tuner
at the unterminated beverage, fed abt 1 W to it, tuned it for 1:1 SWR. Then
disconnected antenna and replaced it with series string of resistors (non-
inductive) and selected the value that gave me 1:1 match again. Measured the
resistance, and that was the value of terminating resistor that went at the
end. The same impedance would then apply to matching transformer.
If you have room for beverages, forget the alternative antenna junk (exc. see
below). Add some reflectors to the slopers and some low Inverted Vee or Delta
Loop, and you would have very versatile arsenal.
Just for illustration: when I was at VE1ZZ (as VA1A), XZ1N was coming through
over 180 degree azimuth (I had 8 beverages for that span) and at the times it
would peak at one direction and few minutes later at another direction (I
spend hour calling, never got him - precious multiplier.) Be aware that Condx
can peak to any area of the world just for a few minutes or even seconds. And
you will never have enough antennas!!
Good luck, have fun
Yuri Blanarovich
K3BU, VE3BMV, VE1BY, VA1A, P40A
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