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From: Andy Talbot <andy.g4jnt@gmail.com>
Date: Fri, 7 Sep 2018 15:50:42 +0100
Message-ID: <CAA8k23R5XYkiN25CR4NS0s7-FrnTGQPLXPkOieRf-gM=e9x=Dg@mail.gmail.com>
To: LineOne <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Sine wave/Sq wave
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When I did this, for the -4dBm out from a DDS source, I designed a custom
filter for the DDS anti-aliassing that had asymmetric termination
impedances and provided a voltage step-up. (AADE filter designer allows
this option)    Then into a  line receiver - I forget which type exactly,
there are millions all suitable.  Built back in 2000 or thereabout and
still working to this day on 137kHz. For low level from a transceiver
output, you could use a step up transformer into, say 300 ohms, for a
voltage magnification of 2.5 ish

Andy
www.g4jnt.com


On 7 September 2018 at 15:42, Andy Talbot <andy.g4jnt@gmail.com> wrote:

> 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">When I did this, for the -4dBm out from a DDS source, I de=
signed a custom filter for the DDS anti-aliassing that had asymmetric termi=
nation impedances and provided a voltage step-up. (AADE filter designer all=
ows this option)=C2=A0 =C2=A0 Then into a=C2=A0 line receiver - I forget wh=
ich type exactly, there are millions all suitable.=C2=A0 Built back in 2000=
 or thereabout and still working to this day on 137kHz. For low level from =
a transceiver output, you could use a step up transformer into, say 300 ohm=
s, for a voltage magnification of 2.5 ish=C2=A0</div><div class=3D"gmail_ex=
tra"><br clear=3D"all"><div><div class=3D"gmail_signature" data-smartmail=
=3D"gmail_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=
=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 15:42, Andy Talbot <s=
pan dir=3D"ltr">&lt;<a href=3D"mailto:andy.g4jnt@gmail.com" target=3D"_blan=
k">andy.g4jnt@gmail.com</a>&gt;</span> 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">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 Sc=
hmitt thresholds at 30% and 70% of supply volts, which if 5V needs at least=
 2V pk-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 is=
h) , but even those are too far apart to absolutely guarantee getting a squ=
are wave from 0dBm<div><br><div>A line receiver, like the 26LS32 mentioned =
or a CMOS equivalent has 100mV or 200mV hysteresis and does a much better j=
ob.</div><div><br></div><div>Or even an opamp with a bit of positive feedba=
ck for a few tens of mV=C2=A0 hysteresis.</div></div></div></div><div class=
=3D"gmail_extra"><br clear=3D"all"><div><div class=3D"m_3189767249358757186=
gmail_signature" data-smartmail=3D"gmail_signature"><div dir=3D"ltr"><div><=
div dir=3D"ltr"><div><div dir=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.g4=
jnt.com" target=3D"_blank">www.g4jnt.com</a></span><br></div><div><br></div=
></div></div></div></div></div></div></div></div></div></div></div><div><di=
v class=3D"h5">
<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></div></div>
</blockquote></div><br></div>

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