[Lowfer] USA loop details

[Bill Ashlock]

Hi Paul,

>2) Voltage across 50 Ohm resistor at feeding loop.  6.5 volts

Are you saying that you have a transmitter in the shack and are feeding the 
loop stepdown transformer (located at the loop) with a coax feed line?  
....And the voltage at the end of the coax is 6.5v p-p when loaded with a 50 
ohm resistor? This calculates to 100mw so I figure this what you are doing.

Since you have a 10 to 1 transformer ratio (or a 100 to 1 impedance ratio) 
you are figuring the 5/8" loop has an Rac of 0.5 ohms. That's about 2x 
higher than I would have figured but not a big deal at the moment.

When you changed to the 7/8" loop conductor and found the transformer ratio 
increased to 14 to 1 (196 to 1 impedance ration) that amounts to a loop Rac 
of 50/196 = approx .25 ohms. Since the ERP is proportional to the Rac that 
would be a 3 db improvement at a distance receiving sight.

So what happens to the loop current? Since Isq = .1/Rac the current should 
have gone up by 1.4X if the Rac dropped by 1/2.  I figure you have a problem 
in you current transformer. What are you using for a core? Also, are you are 
loading it with a resistor that reflects back a small portion of .25 ohms? 
For example: If you have 50 turns and the load resistor is 100 ohms the 
reflected resistance is 100/2500 = .04 ohms and would be marginally OK.

BTW, with a coax feed one can expect all kinds of weird effects from line 
mismatch at all but the exact res freq of the loop. Not nice to try and fool 
mother nature. <G>

Bill A

PS: USA is looking good! Minimal FM tonight.

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