Message-ID: <4DD009E3.3060503@iup.uni-heidelberg.de>
Date: Sun, 15 May 2011 19:14:11 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org
References: <80703.53770.qm@web28515.mail.ukl.yahoo.com> <EE1078C1AE1542A39B4A6054378AA79F@lindavideo> <4DCEDBB3.1020808@iup.uni-heidelberg.de> <D6B1B6FB2BE84EE5A37FB6B8A3522D5A@lindavideo> <4DCFA642.5070305@m0dts.co.uk>
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Subject: Re: LF: LF SWR Bridge
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Hello Rob,

Instead of a SWR bridge i would recommend a voltage/current and a phase 
meter. The voltage/current ratio should be 50:1, so you can easily check 
for 50 Ohm. As i started with LF in 2003 i found that pdf from Jim/M0BMU 
with a good description. The advantage of that tuning meter is that you 
can see if the mismatch is caused by a reactive part (= not in 
resonance) or due to an impedance that is not equal to 50 Ohm.
I'm not sure if the link is still working but i found the pdf in my old 
LF folder and put it to 
http://dl.dropbox.com/u/19882028/LF/LFtunemeter.pdf ...if you want to 
take a look there...

73, Stefan/DK7FC



Am 15.05.2011 12:09, schrieb Rob, M0DTS:
> Hi All..
>
> I'm trying to put together my 137KHz transmitter after it has gathered 
> dust in the loft for a few years and will hopefully generate some 
> signals again soon..
> I'm not so good with this LF so need a bit of help with an swr 
> bridge..  This will stop me blowing FET's this time i hope!
>
> I've seen a couple of designs for an swr bridge and have tried out 
> G0MRF's one here <http://www.g0mrf.com/lfswr.htm> which appears so 
> simple who could go wrong?!
>
> I'm using a 3c90 core,  a very small one (13mm) but i should be able 
> to get the same effect I'm sure,  i just can't get any difference 
> between forward/reflect at all with 50R on the load port..  the only 
> difference i have in my build is the different core size.
> I've tried increasing the bifiliar turns but just gave more coupling 
> as you would expect..
>
> I guess I'm just very low on inductance by using the different core so 
> the q is too low and i don't 'see' the dip in reflected signal when tuned?
>
> Any ideas and a simple explanation of how it works would be useful..
>
> Thanks
>
> Rob
> M0DTS
>

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Hello Rob, <br>
<br>
Instead of a SWR bridge i would recommend a voltage/current and a phase
meter. The voltage/current ratio should be 50:1, so you can easily
check for 50 Ohm. As i started with LF in 2003 i found that pdf from
Jim/M0BMU with a good description. The advantage of that tuning meter
is that you can see if the mismatch is caused by a reactive part (= not
in resonance) or due to an impedance that is not equal to 50 Ohm.<br>
I'm not sure if the link is still working but i found the pdf in my old
LF folder and put it to
<a class="moz-txt-link-freetext" href="http://dl.dropbox.com/u/19882028/LF/LFtunemeter.pdf">http://dl.dropbox.com/u/19882028/LF/LFtunemeter.pdf</a> ...if you want to
take a look there...<br>
<br>
73, Stefan/DK7FC<br>
<br>
<br>
<br>
Am 15.05.2011 12:09, schrieb Rob, M0DTS:
<blockquote cite="mid:4DCFA642.5070305@m0dts.co.uk" type="cite">
  <meta content="text/html; charset=ISO-8859-1"   http-equiv="Content-Type">
  <title></title>
Hi All..<br>
  <br>
I'm trying to put together my 137KHz transmitter after it has gathered
dust in the loft for a few years and will hopefully generate some
signals again soon..<br>
I'm not so good with this LF so need a bit of help with an swr
bridge..&nbsp; This will stop me blowing FET's this time i hope!<br>
  <br>
I've seen a couple of designs for an swr bridge and have tried out
G0MRF's one <a moz-do-not-send="true"   href="http://www.g0mrf.com/lfswr.htm">here</a> which appears so simple
who could go wrong?!<br>
  <br>
I'm using a 3c90 core,&nbsp; a very small one (13mm) but i should be able to
get the same effect I'm sure,&nbsp; i just can't get any difference between
forward/reflect at all with 50R on the load port..&nbsp; the only difference
i have in my build is the different core size. <br>
I've tried increasing the bifiliar turns but just gave more coupling as
you would expect..<br>
  <br>
I guess I'm just very low on inductance by using the different core so
the q is too low and i don't 'see' the dip in reflected signal when
tuned?<br>
  <br>
Any ideas and a simple explanation of how it works would be useful..<br>
  <br>
Thanks<br>
  <br>
Rob<br>
M0DTS<br>
  <br>
</blockquote>
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