[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Linrad] Re: Linrad and MAP65-IQ Calibration

Fantastic, Leif.
This is something every SDR-IQ owner needs to do!

Linrad on my system was reading high by about 330Hz due to a slight
error in the sampling frequency of the SDR-IQ,
and the MAP65-IQ narrow waterfall was also a bit out.

This is what you do to fix it.

1. Find a reliable signal source of accurately known frequency.
GPS-locked SigGen, WWV or whatever.
I used my SigGen on 144.125MHz (or 28.125MHz).

2. Run SpectraVue and note the exact frequency measured by it.

3. Go into SDR-IQ setup in SpectraVue, and use the built-in calculator
to find the actual SDR-IQ sampling frequency.
SpectraVue will apply the correction automatically. My sampling
frequency turned out to be 66.665840MHz.
I had assumed, reasonably, that this correction was only made in
SpectraVue, but not so!
It is actually written to non-volatile RAM in the SDR-IQ.

4. Close SpectraVue and run Linrad. The frequency should now be
correct: 28.125MHz.

5. Open MAP65-IQ and set Fcal to give the correct reading on the
narrow waterfall.
In my case this would be -270Hz with the QSO frequency on 124.
i.e. 124 + 1.270 - 0.270 gives 125. I had to set Fcal to -376Hz.

There will still be a drift of a few Hz as the crystal in the SDR-IQ
warms up - no oven!

Thanks for pointing me in the right direction, Leif.

73  Guy  VK2KU

On Apr 2, 3:24 am, Leif Asbrink <l...@xxxxxxxxxx> wrote:

> There is another option. You may use SpectraVue to change
> the contents of the non-volatile RAM inside the SDR-IQ.
> I never did that and I do not know what effects it would
> have, but most likely it would be equivalent to change
You received this message because you are subscribed to the Google Groups "Linrad" group.
To post to this group, send email to linrad@xxxxxxxxxxxxxxxx
To unsubscribe from this group, send email to linrad+unsubscribe@xxxxxxxxxxxxxxxx
For more options, visit this group at http://groups.google.com/group/linrad?hl=en