Re: LF: Re: 137 grabbers

[Daniele Tincani <danieletincani@yahoo.com>]

Minto,

this is the M0AYF page I referred to:

http://www.qsl.net/m0ayf/active-loop-receiving-antenna.html

May be you "stole" the  original schematics from there? :-)

Best regards

Daniele

From: Minto Witteveen <minto.witteveen@gmail.com>
To: rsgb_lf_group@blacksheep.org
Sent: Sunday, August 14, 2011 7:33 PM
Subject: LF: Re: 137 grabbers

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

 

--------------------------------------------------------------------------
Ceterum censeo Carthaginem delendam esse

 

From: Stefan Schäfer

Sent: Sunday, August 14, 2011 19:03

To: rsgb_lf_group@blacksheep.org

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:

Loop antenna: http://www.pa3bca.nl/index.php?option=com_content&view=article&id=10&Itemid=14

From: Minto Witteveen

Sent: Sunday, August 14, 2011 18:03

To: rsgb_lf_group@blacksheep.org

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.

 

73’s Minto pa3bca (grabber at http://pa3bca.pa3bca.nl:8181)

 

--------------------------------------------------------------------------
Ceterum censeo Carthaginem delendam esse

 

From: mal hamilton

Sent: Sunday, August 14, 2011 17:51

To: rsgb

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