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Re: G3RUH Hardware Demod Mk II vs AO40RCV test



Hi Rich,

I agree with you that both demodulators suffer when there are fast changes
in RX frequency, ... but it is not as simple as just tuning for Doppler!

>From what I've seen over many perigee passes is that the Beacon freq leaps
around by itself, .... now this can be put down to:

1). Frequency instability in Rig
2). Frequency instability in Satellite
3). Frequency instability in RX Converter
4). Doppler shift

I've stopped using computer calculated Doppler correction, ... i.e. I don't
control my rig from the computer on S band, ... I use the G3RUH demod up and
down mic clicks, ... the demod says where the rig should be tuned....

... but given that the demod is doing the Doppler correction to actual RX,
... the beacon still leaps around.

>From here on I'm talking a DSP solution not hardware!

Now I like the idea of tuning between blocks, with a fast PC the DSP demod
knows when a block ends and how far off freq the beacon is (at the receive
end), .... exactly in Hz.

If the DSP software could send an event or callback to a radio control
program (like Station) to the effect of: SAFE TO TUNE UP 34Hz, ... then let
the other software bring the radio dead on line in the block gap.

This is better than using the up and down clicks, as this method has
troubles of its own in that you can accidently go out of passband by
accident and not know it.

Breaking the problem into 2, i.e. demod and radio control, allows the burden
to be shared, ... Moe and others don't have to support every radio type and
interface, ... others do that.

So a min spec for a DSP interface to a radio control program would be:

1). Connect: Direct link by event or callback
2). Function CanYouHearTheBird: returns yes or no
3). Callback: SafeToTune up/down X Hz
4). Disconnect

With the above interface a radio control/tracking program could scan the
band for a signal then staty locked on, ... great for unattended operation.

Anyway I'm sure others will have input!

Cheers
Paul

----- Original Message -----
From: "Richard D. Burgan" <wc8j@raex.com>
To: <paul.willmott@omsl.bm>
Cc: <dak@ioa.com>; <amsat-bb@AMSAT.Org>
Sent: Monday, January 22, 2001 18:24
Subject: Re: [amsat-bb] G3RUH Hardware Demod Mk II vs AO40RCV test


> Hi All,
>
> Along the lines of comparison between the G3RUH and the ao40rcv (v-0.3)
modems.
> I tried an experiment this morning that my help us get better at receiving
the
> AO-40 signal.  The two modems perform about equally well as far as I can
tell.
> However, they are both sensitive to sudden frequency changes caused by
digital
> auto tuning.  For the first part of this mornings pass I tuned manually.
My
> receiver is an ICOM 275 which has 100 Hz steps.  So, I only tuned
*between* data
> blocks and let the receiver (doppler) drift while receiving data.  I got
nearly
> perfect copy.  Of course it was also the very best part of the orbit and I
would
> have had pretty good copy anyway.  I feel that the between block tuning
improved
> things a lot.
>
> Moe Wheatley's ao40rcv.exe program has a new provision to do auto tuning
via the
> handshake lines of a serial port.  I believe it also has a provision to
take
> advantage of the tuning command timing.  As soon as I have time I will try
using
> it to tune my receiver.
>
> 73's de Rich @ WC8J
>
> ----
>
> paul.willmott@omsl.bm wrote:
>
> > http://www.qsl.net/ae4jy/ao40rcv.htm
> >
> > -----Original Message-----
> > From: David Kent [mailto:dak@ioa.com]
> > Sent: Monday, January 22, 2001 10:58 AM
> > To: paul.willmott@omsl.bm
> > Subject: Re: [amsat-bb] G3RUH Hardware Demod Mk II vs AO40RCV test
> >
> > Paul,
> >
> > sorry for the intrusion, but I'd be curious to know if the software
> > demodulator referred to as AO40RCV is the "French demodulator" or
another
> > one ? If another where can it be obtained ?
> >
> > Regards,
> >
> > David Kent / k4uja
> > dak@ioa.com
> >
> > ----- Original Message -----
> > From: <paul.willmott@omsl.bm>
> > To: <amsat-bb@AMSAT.Org>
> > Sent: January 22, 2001 8:40 AM
> > Subject: [amsat-bb] G3RUH Hardware Demod Mk II vs AO40RCV test
> >
> > > Hi All,
> > >
> > > This morning I ran both the AO40RCV software demodulator and my G3RUH
> > > Hardware demodulator at the same time from the same audio source, ....
the
> > > hardware won by only 3 CRCC OK blocks!
> > >
> > > Total scores:
> > > AO40RCV: 45 CRCC OK out of 115 received
> > > G3RUH: 48 CRCC OK out of 121 received
> > >
> > > The usual post-perigee pass is good at start, then 2 MAs of spin mod,
the
> > > good again
> > >
> > > Both were neck and neck until the 2MAs pf spin mod, ... when the good
> > > signals started again the G3RUH was back with CRCC OK, but AO40RCV
didn't
> > > get any, ... then I went to work so didn't get the end of the pass,
... so
> > > this is not a totally conclusive test, ... I would expect DSP to work
best
> > > under noise conditions, ... like MA20 onwards! That test to come.
> > >
> > > I was unable to listen passed MA13 because I had to go to work, ...
but
> > > shows there is very little difference between top end hardware and
Moe's
> > > AO40RCV software solution.
> > >
> > > I will continue to test both side by side for a while to see if either
one
> > > can be optimized either by audio level, audio tone, method of staying
on
> > > frequency etc.
> > >
> > > If your software decoder doesn't write log files in the AMSAT Archive
> > > format, then try out Moe's program as it is 100% compatible with
archive,
> > > and works great! You can find the download link on the telemetry page
on
> > > www.amsat.org
> > >
> > > Cheers
> > > Paul, VP9MU
> > >
> > >
> > > ----
> > > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> > >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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>
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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>

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