Stefan, LF
Not my own design, I don’t remember exactly where I got it but I am
pretty sure I stole the idea ‘from the Internet’ and possible made some changes.
The bc337 was used as I have a lot of them lying around, and they are much
better than for instance the bc547 (my other jellybean transistor).
The
reason I used a -43 type toroid is because I built it for use on 500 KHz and up.
Especially for 80 and 40 meters.
Type-43 is better here than Type-77. On HF this loop is _much, much_ better than
my end-fed TX wire in terms of S/N. The wire picks up a lot of noise from the
house (and from my neighbors houses). The loop is placed to null- out this QRM
as much as possible.
Above 10 MHz the gain drops off rapidly, it is nearly
useless at 14 MHz. a -77 type would be much worse there I think.
As for the
Q: I did a comparison between an FT50-43 and a 14 mm 4C6 (for my 137 KHz
low-pass filter, see my website). The Q of the FT50-43 coil was abt 50, the 4C6
– with a lower Al - was 140 !! Needed more turns ofcourse. On the other hand the
Q of this toroid is not very important here as it is used as a broad-band
transformer.
This is only my hobby… Originally I am a Civil Engineer (but my job
now is in IT).
73’s Minto pa3bca
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Ceterum
censeo Carthaginem delendam esse
Sent: Sunday, August 14, 2011 19:03
Subject: Re: LF: Re: 137 grabbers
This
looks like a very good design. Fascinating easy!! Is it completely grown in your
head or have you seen it somewhere in the web?
What is the gain, about? I
know the BC337 as a low noise NPN transistor.
Your loop is 2m diameter? How
many dBs is the background noise abovethe soundcard noise?
Another
question: Why are the T37-43 (the 43 types in general) preferred to the 77
types? The 77 types have a higher AL value and should come out with less turns.
I tried to wind a band pass coil with but of the types (T50-43 and T50-77) and
achieved about the same Q. Is it just a question of an available
distributor?
And what is your job? Do you have to design electrical
circuits? ;-)
73, Stefan/DK7FC
Am 14.08.2011 18:07,
schrieb Minto Witteveen:
Sent: Sunday, August 14, 2011 18:03
Subject: Re: LF: 137 grabbers
Mal, LF,
I am now using a single-turn loop in the backyard (hight abt 2 meters)
instead of the miniwhip.
One of these days I will test again with the
miniwhip. First impression (testing the noise against DCF39) was that they
dont differ very much.
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Ceterum
censeo Carthaginem delendam esse
Sent: Sunday, August 14, 2011 17:51
Subject: LF: 137 grabbers
LF
My signal seems consistant on the PA3PCA grabber but
varies a lot on the DK7FC grabber, sometimes stronger on this grabber and
others like now barely visible. Could it be the type of antenna in use ie one
is more prone to noise es qsb than the other?
de
mal/g3kev
