SDRplay RSPduo and IQ and/or Smart Blanker calibration

[rsku...@gmail.com]

I have an SDRplay RSPduo that I use on mediumwave and I want to get the Smart Noise Blanker calibrated so that it becomes selectable.

First, do I need to do an IQ calibration first?

Then if so or not, I would need to do a calibration on the Smart Blanker.

I see references to a pulse generator. I can get one, but what would be the frequency I'd select for the RF output of the generator and what is the pulse duty cycle? A square wave or shorter pulses?

Any sort of a cookbook on the above would he a big help.

Thanks in advance,

Rick Kunath, K9AO

[Earl Shaffer]

Hi Rick.

Yes. I Q cal first.

A simple pulse generator for Linrad calibration.

Linrad NB calibration for IQ+ Dual Channel Receiver

73 Earl Shaffer, WB9UWA.

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[Rick Kunath]

Thanks Earl. 

As to the generator, I can get my hands on a signal generator. So what would you set the pulse width to and the frequency to run the calibration then?

Rick

Sent from my iPhone

On Dec 16, 2025, at 4:20 PM, Earl Shaffer <wb9...@gmail.com> wrote:



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[Earl Shaffer]

Hi Rick.

It's been years since I tried this procedure.

I think there are very specific considerations for it so maybe your pulse generator will not be ideal.

Leif has a lot of information on his pages on this. I built his circuit and it worked. I believe the pulse generator was variable.

When you calibrate, you should have as many frequency determining devices in line as possible because some of them may stretch pulses.

I do recall that levels are critical. It's easy to overload an SDR with broadband pulses.

73, Earl.

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[john....@gmail.com]

Hi Rick,

Leif's videos on Setup and calibration are very useful.  https://sm5bsz.com/linuxdsp/videos.htm

If you don't want to build the pulse generator, this video on using a square wave from a function generator for calibration may be useful.

https://youtu.be/FP7VNCnCLuA

I have found the "dumb" blanker to be adequate for most impulse noise.

73,

John N2NC

[Rick Kunath]

I see he has a 20 MHz span of pulses, so I don't know if that is some
kind of a sweep generator, it doesn't look like it could be. Or just
something with a lot of harmonics. I can't see the settings on that
generator to see any of that?

Rick Kunath, K9AO

[john....@gmail.com]

He is using a square wave output from a function generator.  The edges of the square wave generate the harmonics.  The initial calibration was done with a square wave of around 360 Hz.  When you do the calibration, you can see a number "PFR" on the Linrad screen, which is the pulse repetition frequency.   A 360 Hz square wave has one negative to positive and one positive to negative edge each period.  This means the PRF is twice the square wave frequency, about 720 Hz.  At around the 33 minute mark in the video, the function generator is increased to 1.1 KHz to increase signal to noise ratio of the calibration signal.  The PRF increases to 2200 Hz.

73,

- John N2NC

[Rick Kunath]

Great John,

I understand all of that I just was not able to see what he had that
generator set to.

That will be enough to get me going.

Thanks again.

Rick Kunath, K9AO