HF Loop Antennas
 

Is a loop antenna a way to get a "long" antenna in limited space? I am
having a hard time finding detailed information on loop antennas. I
have seen some references to using a long wire, but making several
loops which requires much less space.

And the second question is about feed lines. Could I connect 450 ohm
ladder line to the ends of the loop(s) and then run it to a balanced
tuner in my shack? Most references I have seen about loop antennas talk
about capacitors installed at the loop.

Any insight will be appreciated.

Thanks, jimbo

On 19 Feb 2005 16:39:02 -0800, "jimbo" wrote:

Is a loop antenna a way to get a "long" antenna in limited space? I am
having a hard time finding detailed information on loop antennas. I
have seen some references to using a long wire, but making several
loops which requires much less space.

Hi OM,

That is one way, but if you mean making several turns (loops?) the
topic will become muddied by what is meant by "loops."

And the second question is about feed lines. Could I connect 450 ohm
ladder line to the ends of the loop(s) and then run it to a balanced
tuner in my shack?

Sure, no big deal, you run the same assortment of difficulties and
benefits, just at different frequencies.

Most references I have seen about loop antennas talk
about capacitors installed at the loop.

Ah! Now we are back in the mud of discussion. Those are SMALL loops.
You know, like 1M across.

So, to avoid further difficulties, just what size of a loop are you
thinking? Loop OR dipole, offering the prospective size makes a
considerable difference to the accuracy of responses.

73's
Richard Clark, KB7QHC

Thanks for your reply.

Well, for example, if I wanted a chance on 40-160 meters, I would need
a fairly long dipole, maybe 80 feet on each "wing". But maybe a square
"loop" with four turns only 10 feet on a side would also work?

jimbo

Richard Clark wrote:
On 19 Feb 2005 16:39:02 -0800, "jimbo" wrote:

Is a loop antenna a way to get a "long" antenna in limited space? I
am
having a hard time finding detailed information on loop antennas. I
have seen some references to using a long wire, but making several
loops which requires much less space.

Hi OM,

That is one way, but if you mean making several turns (loops?) the
topic will become muddied by what is meant by "loops."

And the second question is about feed lines. Could I connect 450 ohm
ladder line to the ends of the loop(s) and then run it to a balanced
tuner in my shack?

Sure, no big deal, you run the same assortment of difficulties and
benefits, just at different frequencies.

Most references I have seen about loop antennas talk
about capacitors installed at the loop.

Ah! Now we are back in the mud of discussion. Those are SMALL
loops.
You know, like 1M across.

So, to avoid further difficulties, just what size of a loop are you
thinking? Loop OR dipole, offering the prospective size makes a
considerable difference to the accuracy of responses.

73's
Richard Clark, KB7QHC

On 19 Feb 2005 17:33:29 -0800, "jimbo" wrote:

Well, for example, if I wanted a chance on 40-160 meters, I would need
a fairly long dipole, maybe 80 feet on each "wing". But maybe a square
"loop" with four turns only 10 feet on a side would also work?

Hi OM,

Anything will work, if only to boil an egg. Your problem with a small
loop (and for 160M this so constitutes one) is in the proportion of
losses. If you do your absolute best, you may enjoy 20dB down from a
full size design. If you do better, the loss may not be that bad.
Nearly every successful 160M design that has been crowed about here
was a vertical.

Efficiency is correlated to area, not windings. We've had design
contests here in attempts to crush as much wire into the smallest
footprint to achieve parity with a full size design. As I recall, a
half sized antenna was about as good as it got before you went over
the cliff of diminishing returns.

73's
Richard Clark, KB7QHC

jimbo wrote:
Well, for example, if I wanted a chance on 40-160 meters, I would need
a fairly long dipole, maybe 80 feet on each "wing". But maybe a square
"loop" with four turns only 10 feet on a side would also work?

Single turn loops are more popular than multi-turn loops
because they are more efficient. Small loops are about
0.1 wavelength long usually resonated with a vacuum
capacitor.
--
73, Cecil http://www.qsl.net/w5dxp


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Small transmitting loops can work fairly well above a few MHz, but they
are expensive to make. They need very low loss (because the radiation
resistance is almost nil) and a very high-voltage (10's of kV)
motor-driven capacitor arrangement. You can easily buy them
commercially covering 10 MHz - 30 MHz. They are an option if you don't
have space for a large antenna, don't mind shelling-out $380+ bucks,
and don't mind re-tuning whenever you change operating frequency.

I understand the H-fields are huge close-in, so one needs to be
careful.

73
-JJ