[Lowfer] Loop antenna question

[John Andrews]

All,

I believe that the info in this email thread is correct. If you maintain 
the same area for the loop, and go to N turns, the output voltage will 
be N times the single-turn voltage. The impedance will go up as N^2. 
This will raise both the resistance and the reactance: a 2-turn loop 
that had a single-turn impedance of 1 +j5 Ohms will show 4 +j20 Ohms.

A lesser-appreciated idea is that a transformer can accomplish the same 
thing. A proper 1:2 transformer that has winding reactances at least 5 
times the impedance involved will make the same transformation as adding 
a second turn. I first found out about this in an article by Jim Moritz, 
M0BMU, many years ago.

Here at my MA QTH, I have a single-turn loop, 5' in diameter, feeding a 
3:30 turn transformer. That scales the impedance by a factor of 10^2 = 
100 from the single-turn value, and multiplies the output voltage by 10. 
Since I'm only using the loop to monitor my TAG beacon in Maine, I 
series-tune the loop with an 1800 pF capacitor into a 1:2 transformer to 
get very close to 50 +j0 Ohms. That runs into a 20 dB ("W1VD") 50 Ohm 
preamp in the shack, and then into an Icom R75. Much more signal level 
could be had by parallel-tuning the loop, and running through a high 
input impedance amplifier at the loop. The present arrangement works for 
me, however.

John, W1TAG