[Elecraft] Magnetic Loop Performance

[Bob Novas]

John  - when you say 4 turn coil around the copper pipe, what exactly do you
mean?  What I'm wondering is, what is the orientation of the 4 turn loop
with respect to the copper tubing loop?  You don't mean that you wound the 4
turns around the copper pipe do you?  The two loops should be in the same
plane, perhaps offset, but you should be able to stick a rod through both
loops.

Bob - W3DK

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
johnpierce
Sent: Monday, October 24, 2016 8:23 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] Magnetic Loop Performance

I could use some help with a MagLoop.  I constructed a 48" loop from 3.8"
copper pipe.  I have a 51 pf capacitor across the open end of the loop.  I
am feeding the loop with a 4 turn coil around the copper pipe opposite of
the capacitor.  Before checking the loop I tested a carbon resistor on the
balun (ant side).  Using a 50ohm resistor on the ant side of a 1:1 Balun
which was fed with a 2' piece of 50 ohm coax and with the loop disconnected
I get the following readings from a MFJ 259B antenna analyzer:

 

Freq      Resistance          X

9.7mhz 66ohm                0

10          68                        0

12          77                        0

14          89                        0

17          109                      0

21          126                      0

27          128                      0

27.6       78                        0

 

Reattaching the feed coil and the balun I get the following readings

Freq      Resistance          X

9.7mhz 18ohm                77

10          20                        81

12          43                        119

15          163                      203

16          303                      282

16.5       406                      120

16.56    440                      0

17          547                      0

21          >650

21.3       467                      114

24          95                        191

27          38                        129

27.6       34                        120

29.1       21                        104

 

I ran all these test trying to find out what the resonance is for my 51pf
capacitor.  Rather

than helping me, I am more confused.  I was not finding anything like the
normal response

I have been led to believe I should experience with a magloop.  E.g. peek
noise at the resonance frequency.

 

John

AD2F

 

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