David,
There's a free tool from Analog Devices called the ADIsimRF that will let
you do a similar RF System Analysis. It's not as feature rich, and needs a
windows machine to run, but it'll let you compute these important
performance metrics.
At the end of the day the math doesn't turn out to be too hard for these
things, and is covered in many RF design textbooks. I've found Microwave
Engineering by Pozar to be an excellent companion for building a radio, one
that doesn't shy away from the math.
Chris
On Thu, Feb 26, 2015 at 12:46 AM, Helmut <[email protected]> wrote:
> Hi David,
>
> for the estimation I used a commercial tool called SysCalc, developed by
> Arden Technologies, Inc. The input data have been assumed: Frontend BPF:
> typ. 2 dB NF, 2 dB insertion loss, OIP3 50 dBm; NE6o2: 5 dB NF, 17 dB gain,
> -12 dBm OIP3; channel filter: 3 dB NF, 3 dB insertion loss, OIP3 100 dBm;
> ADC: 50 dB NF (!)
>
> My only intention was to prevent disappointment, hi.
>
> 73, Helmut, DC6NY
>
>
>
> -----Ursprüngliche Nachricht-----
> Von: David Rowe [mailto:[email protected]]
> Gesendet: Mittwoch, 25. Februar 2015 23:08
> An: [email protected]
> Betreff: Re: [Freetel-codec2] Simple SDR for VHF FreeDV
>
> Hi Helmut,
>
> Can you please tell me how you worked that out? My next step is to add
> gain
> to balance MDS and IP3 but not sure how you obtained those numbers!
>
> Yes the radio as it stands requires another design pass. At this stage it
> is a "proof of concept" to test the novel features: such as the use of a uC
> for most of the tuning, and extreme hardware simplicity.
>
> Thanks,
>
> David
>
> On 26/02/15 08:09, Helmut wrote:
> > Hello David,
> >
> > a rough simulation of that SDR design predicts a rather deaf radio:
> > Total noise figure = 38 dB, MDS=-95dBm @ 12,5kHz System BW, Input IP3 =
> -20 dBm.
> > I would suggest at least a 20 dB preamp with high IP3 performance in
> > front of the ADC. So you will achieve a MDS of -114 dBm. Sure no
> > splendid value, but will detect some VHF signals, hi.
> >
> > 73, Helmut, DC6NY
> >
> > -----Ursprüngliche Nachricht-----
> > Von: David Rowe [mailto:[email protected]]
> > Gesendet: Dienstag, 24. Februar 2015 22:16
> > An: [email protected];
> > [email protected]
> > Betreff: [Freetel-codec2] Simple SDR for VHF FreeDV
> >
> > Hello,
> >
> > To support VHF FreeDV developments I've been working on a really
> > simple and very open SDR architecture for VHF radio:
> >
> > http://www.rowetel.com/blog/?p=3884
> >
> > Glen and Matt - would appreciate you suggestions on appropriate input
> > BPF filtering and a VHF mixer. Also pls let me know if you see any
> > show stoppers in this architecture.
> >
> > Cheers,
> >
> > David
> >
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