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	<Pine.LNX.4.64.1601251349010.27152@paranoid.lipkowski.org>
Date: Mon, 25 Jan 2016 16:29:20 +0000
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From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Cc: rsgb_lf_group@yahoogroups.co.uk
Subject: Re: LF: Direct Upconversion from audio
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Having true baseband as an intermediate step is useful for other bands - in
particular 24GHz where several types of off the shelf surplus equipment
already has an image cancelling mixer, just needing I/Q baseband drive.

Alberto's DSPic solution to generating I/Q baseband signals from voice band
looks promising, so long as it has analogue output and not just SPI drive
for a DDS

Andy  G4JNT


On 25 January 2016 at 13:10, Jacek Lipkowski <sq5bpf@lipkowski.org> wrote:

> Hello,
>
> Why not try it another way: in software upconvert the audio to 20kHz (or
> 40kHz if you have a 96kHz sound card), mix up to 136kHz or 472kHz and
> filter out the remaining sideband which is 40kHz away (or 80kHz). You can
> play with an image suppressing mixer here if you want, but an LC filter
> should be sufficient.
>
> And if you want to use this also for receiving, then you can do it in the
> opposite direction: downconvert to 20kHz, then downconvert to audio in
> software.
>
> The upconversion/downconversion to 20kHz IF can be easily done in software.
>
> Some programs can be persuaded to just tx at this frequency (so no up/down
> conversion). Many programs are opensource, so this would be a matter of a
> simple hack to change the tx frequency.
>
> Others (the ones which can't be easily hacked to tx at 20kHz) can be
> up/down converted via external software. Under linux i would use gnuradio
> and pulseaudio (to route the audio from the program to gnuradio input).
> Under windows the same could probably be done with Spectrum Lab and virtual
> audio cable.
>
> This leaves us with an NE612, some LC filtering and a crystal (the
> upconverter can be made tunable, and the bands are narrow, so we can use a
> fixed frequency source). Seems easier.
>
> VY 73
>
> Jacek / SQ5BPF
>
>
>

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<div dir=3D"ltr">Having true baseband as an intermediate step is useful for=
 other bands - in particular 24GHz where several types of off the shelf sur=
plus equipment already has an image cancelling mixer, just needing I/Q base=
band drive.<div><br></div><div>Alberto&#39;s DSPic solution to generating I=
/Q baseband signals from voice band looks promising, so long as it has anal=
ogue output and not just SPI drive for a DDS</div><div><br></div><div>Andy =
=C2=A0G4JNT</div><div><br></div></div><div class=3D"gmail_extra"><br><div c=
lass=3D"gmail_quote">On 25 January 2016 at 13:10, Jacek Lipkowski <span dir=
=3D"ltr">&lt;<a href=3D"mailto:sq5bpf@lipkowski.org" target=3D"_blank">sq5b=
pf@lipkowski.org</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">He=
llo,<br>
<br>
Why not try it another way: in software upconvert the audio to 20kHz (or 40=
kHz if you have a 96kHz sound card), mix up to 136kHz or 472kHz and filter =
out the remaining sideband which is 40kHz away (or 80kHz). You can play wit=
h an image suppressing mixer here if you want, but an LC filter should be s=
ufficient.<br>
<br>
And if you want to use this also for receiving, then you can do it in the o=
pposite direction: downconvert to 20kHz, then downconvert to audio in softw=
are.<br>
<br>
The upconversion/downconversion to 20kHz IF can be easily done in software.=
<br>
<br>
Some programs can be persuaded to just tx at this frequency (so no up/down =
conversion). Many programs are opensource, so this would be a matter of a s=
imple hack to change the tx frequency.<br>
<br>
Others (the ones which can&#39;t be easily hacked to tx at 20kHz) can be up=
/down converted via external software. Under linux i would use gnuradio and=
 pulseaudio (to route the audio from the program to gnuradio input). Under =
windows the same could probably be done with Spectrum Lab and virtual audio=
 cable.<br>
<br>
This leaves us with an NE612, some LC filtering and a crystal (the upconver=
ter can be made tunable, and the bands are narrow, so we can use a fixed fr=
equency source). Seems easier.<br>
<br>
VY 73<br>
<br>
Jacek / SQ5BPF<br>
<br>
<br>
</blockquote></div><br></div>

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