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Date: Mon, 19 Oct 2015 12:00:26 -0400
Message-ID: <CAMFjj70xJgUDAEfcv3iTLRBTOA2vLVdqt7gtdqyy9knoHzMeHg@mail.gmail.com>
From: Warren Ziegler <wd2xgj@gmail.com>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Cc: "rsgb_lf_group@yahoogroups.co.uk" <rsgb_lf_group@yahoogroups.co.uk>
Subject: Re: LF: Decca Protection circuit
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Yes by all means would love to see a write up, it's the best feature of the
Decca!
I have never blown a FET in  a Decca , despite running it into everything
from a short to an open and many wild reactive impedances! Can't say the
same thing for other protection circuit So!
73 Warren


On Monday, October 19, 2015, Andy Talbot <andy.g4jnt@gmail.com> wrote:

> The overload protection circuit used on the Decca transmitter is a rather
> clever technique involving an over-winding on the output tank, whose output
> is rectified and fed back into the power supply.   The turns (and mutual
> coupling) has to be set up at test.
>
> It is arranged so that above a threshold RF current though the tank coil
> (which is proportional via its Q to the resonant voltage across the coil)
> the rectified voltage from the link winding exceeds the supply volts and
> feeds energy from the tank back into the supply rails.  This loss of energy
> therefore appears as a series resistance in the tank and serves to limit
> the current to safe value.   By monitoring the DC current fed back the
> degree of overload can be seen and being DC, is easy to flag alarms and
> things
>
> It is a bit fiddly to set up at test - ideally if the link coil were 100%
> coupled to the tank coil , the turns ratio would be exactly equal to the
> loaded Q of the tank circuit, but coupling isn't perfect so the turns ratio
> is a bit lower than the working Q.
>
> Apart from using this system on my 700 Watt  137kHz transmitter,
> http://www.g4jnt.com/137tx.pdf  where it works exceedingly well indeed,
> is anybody else using the technique?  And would it benefit from further
> publication and a write up somewhere?
>
> Andy  G4JNT
>


-- 
73 Warren K2ORS
                WD2XGJ
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1

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Yes by all means would love to see a write up, it&#39;s the best feature of=
 the Decca!<div>I have never blown a FET in =C2=A0a Decca , despite running=
 it into everything from a short to an open and many wild reactive impedanc=
es! Can&#39;t say the same thing for other protection circuit So!</div><div=
>73 Warren</div><div><br><br>On Monday, October 19, 2015, Andy Talbot &lt;<=
a href=3D"mailto:andy.g4jnt@gmail.com">andy.g4jnt@gmail.com</a>&gt; wrote:<=
br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left=
:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr">The overload protection =
circuit used on the Decca transmitter is a rather clever technique involvin=
g an over-winding on the output tank, whose output is rectified and fed bac=
k into the power supply. =C2=A0 The turns (and mutual coupling) has to be s=
et up at test.<div><br></div><div>It is arranged so that above a threshold =
RF current though the tank coil (which is proportional via its Q to the res=
onant voltage across the coil) the rectified voltage from the link winding =
exceeds the supply volts and feeds energy from the tank back into the suppl=
y rails.=C2=A0 This loss of energy therefore appears as a series resistance=
 in the tank and serves to limit the current to safe value. =C2=A0 By monit=
oring the DC current fed back the degree of overload can be seen and being =
DC, is easy to flag alarms and things</div><div><br></div><div>It is a bit =
fiddly to set up at test - ideally if the link coil were 100% coupled to th=
e tank coil , the turns ratio would be exactly equal to the loaded Q of the=
 tank circuit, but coupling isn&#39;t perfect so the turns ratio is a bit l=
ower than the working Q.</div><div><br></div><div>Apart from using this sys=
tem on my 700 Watt =C2=A0137kHz transmitter, =C2=A0 =C2=A0<a href=3D"http:/=
/www.g4jnt.com/137tx.pdf" target=3D"_blank">http://www.g4jnt.com/137tx.pdf<=
/a> =C2=A0where it works exceedingly well indeed, is anybody else using the=
 technique?=C2=A0 And would it benefit from further publication and a write=
 up somewhere?</div><div><br></div><div>Andy =C2=A0G4JNT</div></div>
</blockquote></div><br><br>-- <br>73 Warren K2ORS<br>=C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WD2XGJ <br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 WD2XSH/23<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0 =C2=A0 =C2=A0 WE2XEB/2<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0 =C2=A0 WE2XGR/1<br><br>=C2=A0<br>

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