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coupling loop for loop antenna



 
 
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  #1  
Old July 21st 05, 01:31 AM
Jim
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Default coupling loop for loop antenna

i see two different designs on the net for receiving loops. one is to
wind the pickup loop with the main loop, and another is to use a 1/5
size loop off center at the bottom. what are the pros and cons for each
setup? what benefit is there to a pickup winding as opposed to just
inductive coupling to the internal loopstick by proximity?

  #2  
Old July 21st 05, 02:08 AM
-ex-
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Jim wrote:

i see two different designs on the net for receiving loops. one is to
wind the pickup loop with the main loop, and another is to use a 1/5
size loop off center at the bottom. what are the pros and cons for each
setup? what benefit is there to a pickup winding as opposed to just
inductive coupling to the internal loopstick by proximity?

Probably more than anything else the preference would be determined by
what type of radio you're coupling to.

Fer instance...a set with a built-in antenna and no external ant
connection would HAVE TO be done by proximity...or else winding a
coupling loop onto the built-in antenna

A set with external antenna connections only often has no internal ant
to couple to.

There's shades of grey between those two but thats the basic pro/con.

-Bill
  #3  
Old July 21st 05, 09:42 AM
Reg Edwards
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"Jim" wrote in message
...
i see two different designs on the net for receiving loops. one is

to
wind the pickup loop with the main loop, and another is to use a 1/5
size loop off center at the bottom. what are the pros and cons for

each
setup? what benefit is there to a pickup winding as opposed to just
inductive coupling to the internal loopstick by proximity?


==================================

The coupling and main loops behave as the primary and secondary
windings on an impedance matching transformer.

The number of turns is fixed at 1 to 1. So the impedance matching is
done by using different loop diameters.

The 1/5 diameter coupling loop matches the antenna to a 50 ohm
receiver or transmitter.

The large diameter coupling loop matches the antenna to a high
impedance receiver such as 1000 ohms.

Theoretically, the impedance matching ratio is equal to the square of
the loop diameter ratio. The receiver input impedance is usually
known. The trouble is to find the impedance of the loop antenna. But
it is not a critical matter.
----
Reg, G4FGQ


  #4  
Old July 22nd 05, 12:11 AM
Jim
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Default

ok, now i am getting somewhere! first this, i have several cheap
portable am/fm/sw radios. specifically i have sangean ats606, sangean
ats505 and sangean ats818. all have built in antennas and plugs for
external am/sw antennas. i am experimenting with a loop for a versatile
portable antenna. i know that it wont beat an outdoor antenna, but i
want something portable that beats the built in antennas. i am trying to
make a loop for am(mw) and a loop for sw on the same form with a common
output. i could switch the am winding or the sw winding in as needed.
the high or low impedance quality of the different styles of output
winding is interesting also. the high impedance would be useful on sw
when the whip is the only place to connect an antenna to. thanks to all
for their opinions!

 




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