[Lowfer] USA loop details

Sun, 16 Nov 2003 12:18:38 -0500

>It sure is nice to have a guy like Bill around with the abilities to do the
>math in a snap of the fingers. I sure wish I could remember all those
>formulas I used to use years ago.

Mike, come on.....   E = I X R;  P= Isq X R; Impedence ratio is the square 
of the turns ratio. Not exactly rocket science.

Bill
>
>
>-----Original Message-----
>From: [email protected] [mailto:[email protected]]
>On Behalf Of Bill Ashlock
>Sent: Sunday, November 16, 2003 12:39 AM
>To: [email protected]
>Subject: Re: [Lowfer] USA loop details
>
>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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