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TopBand: pennants and flags

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Subject: TopBand: pennants and flags
From: (Larry Molitor)
Date: Tue, 15 Sep 1998 23:36:38 +0100
To K6SE in paticular and everyone in general:

Not to be outdone by Earl's experiments, I thought I'd share some of my own
preliminary work.

Over the weekend, I built and erected a rotatable "flag". It's back down on
the ground having much need mechanical improvements made to it, but it was
up long enough to do some measurments. With the same transformer I used
before and an 820 ohm termination (only resistor I could find on short
notice) I measured 10db F/B on hi end broadcast stations. (1420 and 1580).
I assume this poor performance was due to the wrong termination and poor
alignment of the wires.

After that, I installed another pole for the point (feed) end of the
pennant so that I could "rotate" it. Measured F/B on the same broadcast
stations was 23 and 12 db. Not sure if I was really off the back on the 12
db measurement, couldn't fine tune it!

Tried adjusting the 910 ohm termination to a lower value, F/B degraded
rapidly. May need something a little higher than 910 ohms.

The flag was set up in between the 80 and 160 verticals, 40 ft and 60 ft
seperation respectively. Reference stations were 90 deg off the plane of
the two verticals. The vertical portion of the pennant is about 50 feet
from the 80 vertical, 100 or so from the 160. If I'm getting interaction
from the verticals, I can't tell.

Performance of the pennant on skywave sigs from 1.8 thru 12 mhz varies
wildly. I suspect it is due to wildly varying arrival angles rather than
frequency dependence of the antenna.

One additional point I would like to make clear. Changing the transformer
did NOT help the in-band sky-wave F/B a bit! That is the F/B measured on a
single distant station. What I did experience was a remarkable reduction of
local power line noise and computer birdies regardless of the direction.
This is what I was refering to when I suggested the need for more data in
an earlier post.

My own modeling with  nec-2 based software shows the F/B to be highly
dependant on the termination resistor value and not much else. It also
shows typically about 30 DB max F/B at 25deg. Also wants the termination to
be 700 ohms, and I know that ain't right!

More later as the story unfolds. I just wish it wasn't the middle of
summer/monsoon here. Would be nice to hear some of that DX that everbody
else in the world seems to be working!


Larry - W7IUV

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