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Hi Bob that sounds a good set-up. Excuse my
"telling Grandma how to suck eggs" (as we call it) in my last, but I have seen
many frustrated LF ops after much work and investment in copper, gain little in
ERP :-)) It is all a matter of your local conditions.
Yes the 150' runs of your dipole will make
substantial capacitive top load (~600pF) but I guess they droop, as in an
inverted "V"?? Paralleled wires help, provided they are spaced more than about 3
feet apart, current direction is unimporant as they are not radiating. There are
some interesting measurements on a small antenna at http://g3nyk.ham-radio-op.net/spiraltop.htm.
It was a little impractical because of the windage :-)) but an interesting
experiment, that was stimulated by an article in a Canadian Broadcast
Engineering journal. (I hope all the links work....I have had some
troubles with them)
Laurie G3AQC found the the more top capacity he
could add the lower his ground loss became and he finished with a meander that
gave around 1500pF I believe......at 6pF per metre you can see what that means
in length. By measurement we found that once the ground loss ceased to decrease
by adding extra rods and wire.....doubling the top capacity would further half
the ground loss. The catch was the top-load
needed to be over "clear ground" not foliage (he had a bank of Rhododendrons in
his garden, and had to avoid going over those, or any roofs) The commercial
stations use umbrella loading (CFH Halifax NS) or enormous "fans" at NAA Cutler
Ma. The classic GBR Rugby "figure of eight" was filled-in in later years to
increase the capacity of the 16kHz antenna. This effect does seem to lie
unappreciated by a lot of ops but many can't use it because of lossy trees and
buildings in the region of their antenna.
Of course as you will be well aware at these power
levels insulator loss, and corona starts to be a major concern. I think
Warren has set fire to several lengths of plastic water pipe used as insulators
and spreaders :-))
Best wishes. I am sure that if you make the
West to East crossing on 73kHz you will be the first to do it in that
direction.
Alan
G3NYK
----- Original Message -----
Sent: Wednesday, September 25, 2013 2:01
AM
Subject: RE: LF: TA CW?
Alan; I appreciate your input on 73. It was my idea to
have Warren Zeigler file an app just to see what might happen at our
FCC. I had heard the staff at our FCC was instructed to welcome
experimenters for the lower freqs. Warren filed it but told me
nothing may come of it but they granted us the license! I am using a tube
amp [3cx3000A7] with pi-net output and can make 2 kw easily. But only
have a 90' high tower and at the top is the center feed point of my 75 meter
double extended zepp. I simply short the open wire line which runs
almost vertically and fed it with allot of inductance in series! I
assume the two 150' legs acts as top loading. Ground system is from my
broadcast experience where for field intensity surveys 36" wide chicken
wire was used with a 100' tower most often and a 250
transmitter. Eight 50' chicken wire radials produced
decent field on the midband channels [1000 kHz or so] to measure
from. Here I am using several 150' radials of chicken wire
radials. I hope to stretch some out to 300' but that's going to be about
it at my location. I have made it out to Kansas just two days ago with
solid QRSS 60 sigs daytime. I am running just about 1.5 KW into the
ant. The voltage at the feedpoint draws over a 2" spark to a screw
driver so am about at the power top end I think. Here in the finger lakes
region of NY State the winter ground conductivity goes to 8 or better to the
NE with several finger lakes East of me. If I were on the coast I think
it would be a snap to hit the UK over the salt water. Going to be harder
for me inland here. Any comments would be appreciated-Bob
From: [email protected]To: [email protected]Date:
Wed, 25 Sep 2013 01:16:12 +0100 Subject: Re: LF: TA CW?
Hi Bob, the propagation conditions are very
similar to the other LF bands ....there is skywave but the ground wave is
stronger further. The usual problem is antenna efficiency .....in rounded
figures 73 is 4 times more difficult than 136, which is 10 times more
difficult than 470/500.
Beware of using HF or commercial "folklaw" on
ground systems You MUST measure as you go otherwise you will waste a lot of
time and dollars to no great effect. I measured Ground Loss in experiments
with Finbar early in the 137 era (using a simple
transformer-ratio-arm-bridge), and rolling out "radials" can be a big
mistake.....it all depends on your environment. the first one or maybe two
make a difference then it gets you wont notice the difference To be effective
radials on amateur sizes antennas need to be at least 1/8
wavelength which is over half a mile! Unlike 160m skin depth in the
ground can be 30 feet or more at these frequencies. A lookat commercial VLF
antennas is more helpful. They use massive capacity top loading, but they can
usually choose their site for its suitability.
The only station to make the crossing on 73 when
we still had it on this side was Laurie G3AQC (now SK) He was using 1200W from
an ex Decca Nav TX and a reasonably efficient antenna...... but not that
good.His ERP was probably close to 1watt.
Best of Luck ..... its a pity we will
not get an allocation there again.
Alan
G3NYK (an original UK 73kHz "licence"
holder)
-----
Original Message -----
Sent:
Wednesday, September 25, 2013 12:01 AM
Subject:
RE: LF: TA CW?
Stefan; 73 kHz band is going to be difficult from my
preliminary tests. Seems to be a lack of skywave. I think
skywave is going to be rather scarce and best I am doing so far is out
to Kansas but it is ground wave am sure. Got to get the ground system
rolled out here soon as lawn mowing ends. That should help to
give me more field strength on all the bands. Going to try 73
periodically and see what shakes out! I have worked PA0A on CW by ear
last winter on 500. Yes our 500 licenses go down to 470 region.
In winter we should have no trouble working CW by ear am sure and will be
looking forward to it as you would be even further away from me than
PA. I also worked into N. Ireland and I went to SSB and was heard and
worked Finbar, EI0CL [I forgot the suffix of his call] cross mode as he has
no SSB authorization. Jay, Warren and I work regularly Sunday evenings
on 510 upper throughout the Winter months. I see no takers for
73. Gary has a grabber on 73 for us and using QRSS 500 spec lab and I
tried last nite but never saw a trace. With ground system out this
Winter his grabber may be a winner-Bob
Date: Wed, 25 Sep 2013 00:36:21 +0200 From:
[email protected]To:
[email protected]Subject: LF: TA CW? Hi Bob,
Success! :-) Welcome! :-) Sorry i can't receive on 4000m here
since my receivers are mono band homemade DC converters (for 137 kHz and 472
kHz) and direct sampling receivers at 0...24 kHz. But, i remember you
were the strongest station on MF (is that 472...479 kHz for your licence?)
last season. Are you a CW man as well? Do you think it is realistic to try
for a TA CW QSO? If, then it could work in november to february. So far i'm
only getting sporadic WSPR-2 decodes at WD2XSH/17. My WSPR signal is QRP
though. At least VO1NA copied my signal in GN37OR last year... Worth a
try? I'm continuously doing overnite WSPR-2 tests on 630m. 73,
Stefan/DK7FC Am 24.09.2013 23:45, schrieb Bob Raide:
All;
With Stefan's help I seem to have finally made it
into the group. I am Bob Raide W2ZM with exp. license's for
500, 137, and most recently 73 kHz band.
I am ready to fire up on
72.401 with Qrss 60 if anyone is interested to try for a capture
tonite. Or I can change to 137 if no one is interested in 4000
meters.
500 kHz call-WE2XGR/6, 137-WE2XEB, 73-WG2XRS/4
Thanks all,
Bob
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