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From: David Bowman <davidg0mrf@gmail.com>
Date: Fri, 26 Jan 2018 15:06:07 +0000
Message-ID: <CA+GfORti4JQwF07gwYNWQGac38oFBpkHo-J_Pgz1HAMJNcXFrg@mail.gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Softrock RX divider IC problem, unexpected frequency out
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Hi Chris.
It may be worth going back to the oscillator and making sure the frequency
there is what you expect.
Could be that the divider is working fine, but the input to it is shifting
around.

73

David  G0MRF

On Fri, Jan 26, 2018 at 1:45 PM, Chris Wilson <dead.fets@gmail.com> wrote:

>
>
> Hello  LF and VLF folk!
>
> I have built a couple of Softrock Lite II IF frequency receivers,
> normally they would be used to view another receiver's IF on a
> bandscope, but popularly they are also used on low and medium
> frequencies as stand alone SDR receivers. The MF one works fine. Th LF
> one was intermittent, then failed with high current draw. I isolated
> it to a faulty or shorted divider chip. The original one was marked
> 78C49NM. I couldn't find one of those, so plumped for one from RS
> Components here in the UK, a CD74AC74M96G4, RS part number 662-6939
> The oscillator worked on the bench and from an xtal frequency of 461.5
> kHz gave the expected divide by 4 output of 115.364 or very close.
> Then suddenly it started receiving broadcast stations and the divided
> outputs Q and /Q were on 153.814 KHz! There they remain. Fiddling I
> briefly saw a return to 115.36 Khz, but it was not for long. All
> voltages to it's pins are correct at 5V. I am not sure if it's a
> faulty divider, or a bad connection or short.
>
> Xtal case is grounded and seems stable. R16 in the oscillator changed
> on advice from 22.1k to 10k as they apparently tend to stop running
> with 21.1k there. I attach the schematic. Wrong IC? Details of the
> divider's operation are at http://www.wb5rvz.org/softrock_lite_ii/03_div
>
> The new IC details are at https://uk.rs-online.com/web/
> p/flip-flop-ics/6626939/
>
> I see these frequencies on these pins:
>
> Pin 3 : 464.444 kHz
>
> Pin 11 : 464.444
>
> Pin 12 : 153.814
>
> Pin 8 : 153.814
>
> Pin 2 : 307.625
>
> Pin 2 : 307.625
>
> Is this a random IC fault or does it have some mathematical
> correlation? My maths is pitiful!
>
> Not sure what to do now, I have another IC but before risking pad
> damage thought it prudent to ask, many thanks.
>
> Pins 14 and 2 on the mixer IC show good, 90 degree out of phase square
> waveforms of normal amplitude on a scope, but at 153.814 KHz....
>
> Schematic is at http://www.gatesgarth.com/schematic.jpg
>
>
>
> --
> Best regards,
>  Chris                          mailto:dead.fets@gmail.com
>
>
>

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<div dir=3D"ltr"><div><div><div>Hi Chris.<br></div>It may be worth going ba=
ck to the oscillator and making sure the frequency there is what you expect=
.<br></div>Could be that the divider is working fine, but the input to it i=
s shifting around.<br><br>73<br><br></div>David=C2=A0 G0MRF<br></div><div c=
lass=3D"gmail_extra"><br><div class=3D"gmail_quote">On Fri, Jan 26, 2018 at=
 1:45 PM, Chris Wilson <span dir=3D"ltr">&lt;<a href=3D"mailto:dead.fets@gm=
ail.com" target=3D"_blank">dead.fets@gmail.com</a>&gt;</span> wrote:<br><bl=
ockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #=
ccc solid;padding-left:1ex"><br>
<br>
Hello=C2=A0 LF and VLF folk!<br>
<br>
I have built a couple of Softrock Lite II IF frequency receivers,<br>
normally they would be used to view another receiver&#39;s IF on a<br>
bandscope, but popularly they are also used on low and medium<br>
frequencies as stand alone SDR receivers. The MF one works fine. Th LF<br>
one was intermittent, then failed with high current draw. I isolated<br>
it to a faulty or shorted divider chip. The original one was marked<br>
78C49NM. I couldn&#39;t find one of those, so plumped for one from RS<br>
Components here in the UK, a CD74AC74M96G4, RS part number 662-6939<br>
The oscillator worked on the bench and from an xtal frequency of 461.5<br>
kHz gave the expected divide by 4 output of 115.364 or very close.<br>
Then suddenly it started receiving broadcast stations and the divided<br>
outputs Q and /Q were on 153.814 KHz! There they remain. Fiddling I<br>
briefly saw a return to 115.36 Khz, but it was not for long. All<br>
voltages to it&#39;s pins are correct at 5V. I am not sure if it&#39;s a<br=
>
faulty divider, or a bad connection or short.<br>
<br>
Xtal case is grounded and seems stable. R16 in the oscillator changed<br>
on advice from 22.1k to 10k as they apparently tend to stop running<br>
with 21.1k there. I attach the schematic. Wrong IC? Details of the<br>
divider&#39;s operation are at <a href=3D"http://www.wb5rvz.org/softrock_li=
te_ii/03_div" rel=3D"noreferrer" target=3D"_blank">http://www.wb5rvz.org/<w=
br>softrock_lite_ii/03_div</a><br>
<br>
The new IC details are at <a href=3D"https://uk.rs-online.com/web/p/flip-fl=
op-ics/6626939/" rel=3D"noreferrer" target=3D"_blank">https://uk.rs-online.=
com/web/<wbr>p/flip-flop-ics/6626939/</a><br>
<br>
I see these frequencies on these pins:<br>
<br>
Pin 3 : 464.444 kHz<br>
<br>
Pin 11 : 464.444<br>
<br>
Pin 12 : 153.814<br>
<br>
Pin 8 : 153.814<br>
<br>
Pin 2 : 307.625<br>
<br>
Pin 2 : 307.625<br>
<br>
Is this a random IC fault or does it have some mathematical<br>
correlation? My maths is pitiful!<br>
<br>
Not sure what to do now, I have another IC but before risking pad<br>
damage thought it prudent to ask, many thanks.<br>
<br>
Pins 14 and 2 on the mixer IC show good, 90 degree out of phase square<br>
waveforms of normal amplitude on a scope, but at 153.814 KHz....<br>
<br>
Schematic is at <a href=3D"http://www.gatesgarth.com/schematic.jpg" rel=3D"=
noreferrer" target=3D"_blank">http://www.gatesgarth.com/<wbr>schematic.jpg<=
/a><br>
<span class=3D"HOEnZb"><font color=3D"#888888"><br>
<br>
<br>
--<br>
Best regards,<br>
=C2=A0Chris=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 mailto:<a href=3D"mailto:dead.fets@gmail.com">d=
ead.fets@gmail.com</a><br>
<br>
<br>
</font></span></blockquote></div><br></div>

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