[Lowfer] antennas

[lowfer@mailman.qth.net]

Lyle VE7SL, thanks for the QRSS suggestion. I will get set up for that along 
with regular CW for preliminary tests in the valley here. The MCW is so I can 
hear it on my car radio. MCW does use a lot of spectrum and if this is a 
problem I won't do that. For CW only I can increase the keying risetime to 10 
ms and for QRSS it a second or more.

Perhaps 510 kHz would be fun to try. I have been modeling some antennas and 
the efficiency is awful at 510 kHz using a 2 meter wire with a 1 meter radius 
top hat. And the 10 mH loading coil looks to be an engineering feat. I 
believe I can get better performance using a spiral loading coil at the top. 
This would involve about 600 feet of wire wound with 1 inch spacing. This 
will take a bit of work to model but can be done. Now, if I interpret the 
antenna rules for 600 meters as Lyle, K0LR, mentioned for 1750 meters, (3 
meter cylinder at 600 meters) things would be MUCH nicer.

COMMENTS on interpreting the antenna rules? I don't want to "cheat" the rules 
of the lowfer/medfer game or violate FCC rules.

Stewart, KK7KA: I will run a simulation of your antenna. Do you want to use 
the dimensions you listed or change them? I can then send you the inputs to 
use with Nec-Win+ software. You can download this from AntenneX and use it 
for free for 30 days. As far as antenna physical construction goes, my 160 
meter antenna is a self-supporting 38 foot top loaded vertical. It is made of 
aluminum (available at Texas Towers) and the top-hat has a radius of 6 feet 
with perimeter wires. It is designed to survive a 60 mph wind with gusting to 
80 mph. It folds over when not in use (CC&R neighborhood). I have been 
modeling it as a base-loaded antenna on 1750 meters and a larger top hat with 
top loading would sure help. 

LOADING COILS: The massive 1750 m air-core loading coils (several mH) I have 
modeled seem to have low-Q. If a Q of 100 is all that we can manage, then 
this can be achieved with an inductor using a magnetic core. The main problem 
I see is holding the inductance as the antenna current varies and with 
temperature. These problems can probably be handled. This smaller inductor 
would allow one to more easily top-load an antenna. With that said, can a Q 
of 100 be exceeded with a large air-core coil and has anyone experimented 
with ferrite cores? 

     Dave WX7G


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