First, thank you to the many, many who have commented on
my post about listening results with the NCDXF beacons about
the world, at least those I heard yesterday on 14100.
Summary of points raised:
1. Obviously the best measurement "resolution" I had available
was the 10 dB steps of the various NCDXF beacons. Several of
you suggested that I should use only the 100 watt signal level
plus an accurate step attenuator. I have two wishes: that the
100 watt signal level would last more than the beacon call plus
one second "dah" that it does; and that I had such an attenuator!
Another suggestion was to do the same thing, but forget the beacons,
and actually transmit a signal to another station here on Kauai
where he would use the accurate step attenuator to compare
the "field strength" radiated from the two antennas under
test. Some suggested that one set of data, as I now have,
is inadequate: needs lots of data test lists over a day, and over
a few weeks before going on to adding radials.
Anyone have such an attenuator I could buy/borrow for a
time? Second, nearby station is KH6FMT, perhaps 3 or 4
miles distant, but shadowed a bit by a couple of very low
hills between us, which just hides his QTH area. Would that
work? I have .jpg photo image of that view/direction taken
from just below my TA-34; would be happy to e-mail it to
anyone who might want to comment on the situation
suitability; of course, it is moot without an accurate
attenuator.
2. The background RF noise level out here is VERY low. However,
It is a bit surprising to me, and a few others, that there would
be 40 or 50 dB of "dynamic" or FT-1000D sensitivity range on
down below the "no S meter movement" of the rig!! None of
yesterday's "loudest" beacon signals ever even "tweaked"
the D's S meter. Meter is probably just fine, as it reads the
usual range of expected signal levels in everyday QSO'ing.
The expected actual signal level range from these beacons,
using TS-50's and R5 vertical antennas is in the -70 to about
-125 dBm range. In fact, yesterdays signal levels at the
HAARP station in Alaska from W6WX and ZL6B (the only beacons
they "heard" yesterday) are shown at:
http://www.haarp.alaska.edu/mon/bscany.html
Note that at the time of my measurements, 2000 - 2030
UTC, they had lost the ZL beacon, and the W6 was
fading rapidly. Also notice the range of amplitudes
plotted as these beacons stepped down in power during
each time slot: typically ranging from -85 or so dBm at
100 watts , down to around -115 or so at whatever
signal level they last "heard". Be neat to obtain such
"absolute" numbers from out here.
3. Feed line, connectors, etc to the two compared antennas.
The vertical is on the far end of 250 feet of LMR-400/PL-259's
purchased from The Wireman, Press Jones just about 10
weeks ago now. There is a Top-Ten Devices 6-way remote
switch to which the first 200 feet run; this on the mounting
pole of the TL160 vertical. From the switch, the remaining
50 feet run on to the 20 meter vertical. I actually managed
to "kink" the LMR a couple of times as I was laying it out
back in late April; the stuff is stiff, and wants to return
to the nice big diameter coil to which it was wound at
manufacture, I suppose. Laying out 200 feet is not a
cinch by oneself; hope I didn't do any permanent
damage inside by the couple of kink events.
The TA-34 is being fed with a 100 foot length of about 5 year
old Belden 9913, which runs to the base of the MA-550; then
a 50 foot length of regular RG8 goes up the pole, out on the
boom, coils in 8 turns for a choke balun, and feeds the
Mosley. There are PL's and a barrel connector between
these two 5 year old cables.
4. One comment mentioned that I had forgotten the "ground
reflection" gain available to the TA-34 horizontal antenna that
is not available to the vertical. He thought that would increase
my estimate of the TA's real gain to around 10 dBi; thus he
thought my "measurements" were probably about correct.
5. One suggestion was that I put up a horizontal dipole at
the same height as the TA-34; but which way would I
"broadside" the dipole. It will favor one or another of
the beacons, but not all, unless it were a rotating dipole,
same as the triband beam. Another, wondered what
would result were the 20 meter vertical base elevated
to the 45 foot height of the TA-34.
6. Finally, a couple mentioned that the most gain increase
I just might experience with adding all 32 additional radials
would probably be about 5 dB at most. How would I be
able to tell the difference with my present method?
Guess I probably could not, except subjectively. I really
do need to find a calibrated attenuator somewhere for
it to be worth while to continue this exercise.
Just had a look in the Surplus Sales of Nebraska catalog
obtained in Dayton. They list several attenuators, with
1 dB steps --- hmmm. Most applicable is probably the
Kay 0 - 101 dB, switch selectable in 1 dB increments.
However, has 50 ohm BNC connectors, and is priced
at $165, wow. (pg 34, upper top left page corner).
Well, that is it for now.
73, Jim, KH7M
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