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rickman · October 29th 14, 12:53 AM posted to rec.radio.amateur.antenna

On 10/28/2014 8:18 PM, wrote:
rickman wrote:
On 10/28/2014 6:10 PM, wrote:
In rec.radio.amateur.antenna rickman wrote:
I have a project in mind that would need a very good antenna in the
frequency range of 60 kHz. Originally I looked at loop antennas and
liked the idea of a large shielded loop made of coax tuned with a
capacitor. My goal is to get as large a signal as possible from the
antenna and matching circuit to allow the use of a receiver with very
low sensitivity... in fact an all digital receiver.

I spent some time simulating antennas in spice and was able to get a bit
of a feel for the circuit, but I'm not convinced it would work the way I
want. Just before I set the project aside I was told I needed to model
the radiation resistance. That has the potential of wrecking the Q of
the circuit. I am counting on the high Q to boost the output voltage.
If the radiation resistance is at all appreciable I would lose the high
Q and need to start over.

Anyone have an idea of how to estimate the radiation resistance of a
tuned, shielded loop antenna?

The other factor I don't understand how to factor in is the distributed
capacitance of the coax. Is that a significant influence on an antenna
or is it in the noise compared to the tuning capacitor. The coax is
RG-6-Solid Coax Cable. The loop is made up from 50 feet of this. The
specs are 16.2 pf/foot and 6.5 mOhms/foot in the center conductor, or
would the resistance be a round trip measurement of both inner conductor
and shield? I assume the shield has a much lower resistance than the
inner conductor but I don't know that for sure.

Google DIY WWVB antenna

16,900 results.

As for the output voltage, you do know FET input opamps work quite
well at 60 Khz and are dirt cheap?

FYI for those on the other side of the pond, WWVB is a US 60 kHz time
and frequency station.

Yes, I am familiar with op amps.

How about WWVB and the many existing examples?

Not sure what you are saying. There are tons of examples. But when I
did my search there was very little info on the design of loop antennas.
At least not much in depth enough to let me figure out how much signal
I might get from a given circuit.

I am asking about specific details of loop antenna design. I'm not sure
why people keep suggesting I look at "examples".

--

Rick