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From: Andy Talbot <andy.g4jnt@gmail.com>
Date: Fri, 7 Sep 2018 15:42:08 +0100
Message-ID: <CAA8k23SVM_7D3C5MaEqBrFJ-nuzwozoZhVAaqZfc033cTqPv6Q@mail.gmail.com>
To: LineOne <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Sine wave/Sq wave
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Unfortunately, 0dBm from a 50R source into a Schmitt isn't enough in many
cases.     74HC series logic has Schmitt thresholds at 30% and 70% of
supply volts, which if 5V needs at least 2V pk-pk.  At 50 ohms this is
+10dBm absolute minimum.

74HCT series has thresholds of 1.6 and 2V (ish ish) , but even those are
too far apart to absolutely guarantee getting a square wave from 0dBm

A line receiver, like the 26LS32 mentioned or a CMOS equivalent has 100mV
or 200mV hysteresis and does a much better job.

Or even an opamp with a bit of positive feedback for a few tens of mV
hysteresis.

Andy
www.g4jnt.com


On 7 September 2018 at 15:20, <g3kevmal@talktalk.net> wrote:

> LF/MF
> Someone was asking about converting sine wave to Sq wave recently from a
> TS590 to drive an Amplifier
> Feed the DRV output sine wave  from the TS590 to a Schmitt triger cct and
> then use a Direct Amplifier similar to the Decca 5501 class D bridge amp.
> I use this method on LF es MF and never had a problem.
>
> 73 gl de mal/g3kev
>
>
>

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<div dir=3D"ltr">Unfortunately, 0dBm from a 50R source into a Schmitt isn&#=
39;t enough in many cases.=C2=A0 =C2=A0 =C2=A074HC series logic has Schmitt=
 thresholds at 30% and 70% of supply volts, which if 5V needs at least 2V p=
k-pk.=C2=A0 At 50 ohms this is +10dBm absolute minimum.=C2=A0 =C2=A0 =C2=A0=
<div><br></div><div>74HCT series has thresholds of 1.6 and 2V (ish ish) , b=
ut even those are too far apart to absolutely guarantee getting a square wa=
ve from 0dBm<div><br><div>A line receiver, like the 26LS32 mentioned or a C=
MOS equivalent has 100mV or 200mV hysteresis and does a much better job.</d=
iv><div><br></div><div>Or even an opamp with a bit of positive feedback for=
 a few tens of mV=C2=A0 hysteresis.</div></div></div></div><div class=3D"gm=
ail_extra"><br clear=3D"all"><div><div class=3D"gmail_signature" data-smart=
mail=3D"gmail_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div d=
ir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr">Andy<div><span style=
=3D"font-size:12.8px"><a href=3D"http://www.g4jnt.com" target=3D"_blank">ww=
w.g4jnt.com</a></span><br></div><div><br></div></div></div></div></div></di=
v></div></div></div></div></div></div>
<br><div class=3D"gmail_quote">On 7 September 2018 at 15:20,  <span dir=3D"=
ltr">&lt;<a href=3D"mailto:g3kevmal@talktalk.net" target=3D"_blank">g3kevma=
l@talktalk.net</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" s=
tyle=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir=3D"ltr">
<div dir=3D"ltr">
<div style=3D"FONT-SIZE:12pt;FONT-FAMILY:&#39;Calibri&#39;;COLOR:#000000">
<div>LF/MF</div>
<div>Someone was asking about converting sine wave to Sq wave recently from=
 a=20
TS590 to drive an Amplifier</div>
<div>Feed the DRV output sine wave=C2=A0 from the TS590 to a Schmitt triger=
 cct=20
and then use a Direct Amplifier similar to the Decca 5501 class D bridge=20
amp.</div>
<div>I use this method on LF es MF and never had a problem.</div>
<div>=C2=A0</div>
<div>73 gl de mal/g3kev</div>
<div>=C2=A0</div>
<div>=C2=A0</div></div></div></div>
</blockquote></div><br></div>

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