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Date: Mon, 25 Jan 2016 22:15:41 +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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I already have a voice band to I/Q bit of software.  Written by G3PLX, it
also generates AM and FM using a crafty use of a dummy low frequency tone
at low level to cope with the DC slot.   http://www.g4jnt.com/SDRTxSW.htm

However, I want a non PC based solution for stand alone operation with
beacons and other general tasks.

Works very well.

Andy  G4JNT


On 25 January 2016 at 22:02, Jacek Lipkowski <sq5bpf@lipkowski.org> wrote:

> On Mon, 25 Jan 2016, Andy Talbot wrote:
>
> 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.
>>
>
> You can do this easily in software too in a similar way. Many sound cards
> can be dc-coupled (or at least the coupling caps can be increased, so there
> is only a narrow dip near 0Hz) - i'm not sure about the 1/f and other
> noises near 0Hz, but that should not be too bad. Actually i'm not sure that
> you would need to modify anything for ssb, voice should be understandable
> with a few 10s of Hz gap around 1.5kHz, and digital transmissions can just
> avoid the few Hz around 1.5kHz.
>
> The software is simple: in gnuradio use a frequency xlating fir filter
> with a 1.5kHz frequency and float->complex conversion, feed this into a
> complex-> float block and the outputs into a stereo sound card sink. Very
> simple to draw in gnuradio-companion, you don't even have to do any
> programming (and while you're at it, you can also do a receiver which would
> be equally simple). I suspect this could also be trivially done in Spectrum
> Lab.
>
> 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
>>
>
> Yes, this is great, because you don't need a PC for it. Running gnuradio
> on a raspberry pi would also work (and be easier to modify to your needs),
> but the dsppic solution probably has less latency.
>
>
>
> Still for LF/MF this seems to be too complex, upconverting in software to
> around 20kHz and then to 136/472kHz and LC filtering seems much simpler,
> and can be debugged just with an audio generator.
>
> Example for 2200m band: a cheap 3.686MHz crystal divided by 32 gives
> 115.1875kHz. To transmit on 135.7-137.8kHz you need to generate
> 20.5125-22.6125kHz with the sound card (no problem with a cheap 48kHz sound
> card). The mirror frequency is around 94kHz, so it is easy to filter out
> from the 137kHz output.
>
> Example for 630m band: use a 455kHz crystal (or a piezoceramic if you
> don't mind worse frequency stability). To transmit on 472-479kHz you need
> to generate 17-24kHz (cheap sound card). The worse case mirror frequency
> would be at 17kHz, trying to filter 472kHz and reject 432kHz, still doable
> but with a few more LC circuits (see how much an old AM radio uses for this
> selectivity).
>
> VY 73
>
> Jacek / SQ5BPF
>
>
>

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<div dir=3D"ltr">I already have a voice band to I/Q bit of software.=C2=A0 =
Written by G3PLX, it also generates AM and FM using a crafty use of a dummy=
 low frequency tone at low level to cope with the DC slot. =C2=A0=C2=A0<a h=
ref=3D"http://www.g4jnt.com/SDRTxSW.htm">http://www.g4jnt.com/SDRTxSW.htm</=
a><div><br></div><div>However, I want a non PC based solution for stand alo=
ne operation with beacons and other general tasks.</div><div><br></div><div=
>Works very well.</div><div><br></div><div>Andy =C2=A0G4JNT</div><div><br><=
/div><div><br></div><div class=3D"gmail_extra"><br><div class=3D"gmail_quot=
e">On 25 January 2016 at 22:02, Jacek Lipkowski <span dir=3D"ltr">&lt;<a hr=
ef=3D"mailto:sq5bpf@lipkowski.org" target=3D"_blank">sq5bpf@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">On Mon, 25 Jan 2016,=
 Andy Talbot wrote:<br>
<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">
Having true baseband as an intermediate step is useful for other bands - in=
<br>
particular 24GHz where several types of off the shelf surplus equipment<br>
already has an image cancelling mixer, just needing I/Q baseband drive.<br>
</blockquote>
<br>
You can do this easily in software too in a similar way. Many sound cards c=
an be dc-coupled (or at least the coupling caps can be increased, so there =
is only a narrow dip near 0Hz) - i&#39;m not sure about the 1/f and other n=
oises near 0Hz, but that should not be too bad. Actually i&#39;m not sure t=
hat you would need to modify anything for ssb, voice should be understandab=
le with a few 10s of Hz gap around 1.5kHz, and digital transmissions can ju=
st avoid the few Hz around 1.5kHz.<br>
<br>
The software is simple: in gnuradio use a frequency xlating fir filter with=
 a 1.5kHz frequency and float-&gt;complex conversion, feed this into a comp=
lex-&gt; float block and the outputs into a stereo sound card sink. Very si=
mple to draw in gnuradio-companion, you don&#39;t even have to do any progr=
amming (and while you&#39;re at it, you can also do a receiver which would =
be equally simple). I suspect this could also be trivially done in Spectrum=
 Lab.<br>
<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">
Alberto&#39;s DSPic solution to generating I/Q baseband signals from voice =
band<br>
looks promising, so long as it has analogue output and not just SPI drive<b=
r>
for a DDS<br>
</blockquote>
<br>
Yes, this is great, because you don&#39;t need a PC for it. Running gnuradi=
o on a raspberry pi would also work (and be easier to modify to your needs)=
, but the dsppic solution probably has less latency.<br>
<br>
<br>
<br>
Still for LF/MF this seems to be too complex, upconverting in software to a=
round 20kHz and then to 136/472kHz and LC filtering seems much simpler, and=
 can be debugged just with an audio generator.<br>
<br>
Example for 2200m band: a cheap 3.686MHz crystal divided by 32 gives 115.18=
75kHz. To transmit on 135.7-137.8kHz you need to generate 20.5125-22.6125kH=
z with the sound card (no problem with a cheap 48kHz sound card). The mirro=
r frequency is around 94kHz, so it is easy to filter out from the 137kHz ou=
tput.<br>
<br>
Example for 630m band: use a 455kHz crystal (or a piezoceramic if you don&#=
39;t mind worse frequency stability). To transmit on 472-479kHz you need to=
 generate 17-24kHz (cheap sound card). The worse case mirror frequency woul=
d be at 17kHz, trying to filter 472kHz and reject 432kHz, still doable but =
with a few more LC circuits (see how much an old AM radio uses for this sel=
ectivity).<br>
<br>
VY 73<br>
<br>
Jacek / SQ5BPF<br>
<br>
<br>
</blockquote></div><br></div></div>

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