Jim, LF,
Wow, it works very well!
I took that Litz wire that is a 30x0.1mm wire in my case and wound 55
turns on a double side bonding tape across the PVC tube.
First the Q was low, about 130. I noted that sourrounding metallic
parts have an influence on the Q. Then i placed the rod on a cardboard
box. Q was 160 at 136.5 kHz (took 2.44 nF) but i noted it decreased
continuously. I thought about a thermal drift of the caps that just
have been soldered before.
Then i took a 2.2 nF styroflex cap and achieved a Q of
486!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Unbelivable :-))
For the spectrum and peak, see:
http://dl.dropbox.com/u/19882028/LF/Q.jpg
This is the arrangement (i took a 47 pF cap to inject a white noise
from a NI
PXI-6115): http://dl.dropbox.com/u/19882028/LF/arrangement.JPG
Almost a bit to sharp, isn't it?!
What do you (and others) think?
73, Stefan/DK7FC
Am 16.08.2011 22:36, schrieb Stefan Schäfer:
Jim, LF,
I'll try to go on as fast as the distributor and ebay did ;-) So this
is the current situation:
Decided to use the 2x7 bundle. The cross section area of 7 pcs. just
lokks better :-) Also the complete stick is much more handy and robust.
Markus/DF6NM gave me the hint to overlap the inner rod by 50%. So i
intentionally broke one rod and put the 2 halfs to the inner ends. One
complete one is now in the inner center.
See: http://dl.dropbox.com/u/19882028/LF/ferrite%20antenna%20parts.JPG
I took a simple bonding tape to isolate the rods from each other. The
whole arrangement was fixed by bonding tape and put into a stable and
very proper PVC tube with 2.5 mm thickness, making the rod very robust
and give some distance between winding and ferrite (just as in the
magic antenna article ;-) ).
Ther was even some place to add a bit of that transport foil with the
air bubbles inside, you know ;-) Perhaps this will be some kind of
shock protection (hopefully never needed) and fixed the rods inside the
tube.
http://dl.dropbox.com/u/19882028/LF/inside.JPG
Now the outer dimensiona are 285 mm x 33 mm.
As a first test i wound a simple wire arround the rod, 22 turns.
Resonance C is 11.2 nF and f res = 137,1 kHz. Q = 100 (unloaded).
During the measurement i was irritated by a strange peak near 137.7 kHz
which was my own transmission during that time ;-)
So L must be 120 uH. Not so much...
Will go on now using the Litz wire and start with about 40 turns and
see what comes out. Then i go for 60 turns, maybe 80 if Q is still
rising.
73, Stefan/DK7FC
Am 16.08.2011 19:01, schrieb James Moritz:
Dear Stefan, LF Group,
----- Original Message -----
The 20 mV is the peak level (thus mVp ;-) )
while the mentioned 100 uV is rms.
OK - so that makes your RX noise level 3dB lower, and gives you 3dB
more margin, which is good!
Cheers, Jim Moritz
73 de M0BMU
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