Tony Giacometti wrote in
:

Owen Duffy wrote:

Tony Giacometti wrote in
news:NNydnfODM_iOB6LanZ2dnUVZ_r6rnZ2d@hawaiiantel. net:

...
For what its worth, I have never considered just plain wire for the
loop. I do use coax RG-6 - its all I can get, no RG-59 around here.

Did I miss something. I did see you refer us to a web page that
described the loop using RG59... and now you tell us you used RG6.
You might not yet know it, they are different, and the difference is
relevant.

Owen


I looked at the specs for both cables and the difference is very
small. Thats why I used RG-6, I have no source for RG-59 here.


Tony,

You might regard the difference as small, but in the models that I
created the difference in transmission loss, velocity factor, and shield
diameter are relevant.

Anyway, I have built and calibrated a model of the 80m loop described in
the ARRL Antenna Book (19th ed), and I am still checking the model.

Initial results are that it does exhibit a peak in gain at about 300pF of
tuning C, and that peak in gain is just a little less than an untuned
unshielded loop of the same size.

It looks like the gain is about -53dBi (not including feedline). If the
expected noise from a 0dBi antenna in 2kHz was -83dBm, this would give
around -136dBm which is in the region of the quiet noise floor on a good
HF receiver. Of course, if you were in a very noise place, then this
might be sufficient gain to achieve close to max S/N.

I have also modelled the tuned loop with the LHS shield bonded to the
inner conductor at the gap, which removes the lossy s/c stub from the
picture, increasing gain a little. Now this connection will not appeal to
the people with misconceptions about how a shielded loop works, but the
s/c stub formed by the coax on one side of the loop is just another loss
element that can be avoided.

Made of RG6, the gain is about a half dB higher.

I will look at it later in the day and put some notes together.

Owen