Re: [Discuss-gnuradio] Just wondering why?

[Adrian Hodgson]

Thanks for responding I have posted responses within the text.

On Wednesday, 1 November 2017 20:04:57 GMT Cinaed Simson wrote:
> On 10/30/2017 04:04 PM, Adrian Hodgson wrote:
> > Quite new to this so perhaps a dumb question.
> > 
> > I have the following flowchart Narrow_band_QT.grc and screenshot attached,
> > just something I have been playing with.
> 
> Note, you should set the RF again to 0 when receiving. There's frontend
> on the hackrf and you run risk of smoking the receiving RF amplifier if
> there's a strong RF transmission nearby.
> Also, the RF gain is either 0 or 1 - on or off.
> 
> See the hackrf tutorials greatscottgadgets.com website.
> 
Not a problem for me most of my testing is done with my test set, the RF gain 
set at 14 dB means I can receive signals down to -115 dBm, I tend to use 
signals at around -80 dBm so I am far away from the -5 dBm maximum for the rf 
amp.
I did have a play with my wireless doorbell following on from the smart 
gadgets tutorials and eventually got it to work, but my main use would be 
monitoring the local amateur repeaters, being a licensed radio ham!

> > There are a few variables I use one is band_width.  Now the strange thing
> > is if I start with a default of 100KHz band width when running I can
> > scroll down to 10 KHz bandwidth and then go back up again, but if I start
> > with the default set to 10 KHz bandwidth it will not scroll up to 100KHz.
> > It is more noticeable when looking at the bandwidth tab which is directly
> > after the rational resampler. one can see the pass-band chance width as i
> > change the bandwidth.
> 
> The bandwidth is equal the sampling rate - in your case - 2M.

I think I did not explain myself correctly

I did find two issues with my flow chart, one was that I used one variable to 
feed another variable, so removed that issue.

The second was the QT freq display sample rate after the resampler should have 
been at 240kHz not 2M.  When set to 2450K then the frequency display matches 
the true frequency.

But that still did not resolve the issue I am having.  If I set the default 
band_width variable to 100e3 and run the flow graph, if you go to the 
band_width tab and scroll on the bandwidth number you will see the width of 
passband signal reduce and go back up as you scroll.

But set the default band_width to 10e3 and run the flow graph and it does not 
work.

Attached are modified files.

The grc should run with a rtl2833 as well as a hackrf one, at least I believe 
so as I use the osmocom source block.

> 
> Look at with hackrf WBFM tutorial greatscottgadgets.com website.
> 
Went through that.

> The channel width of the NBFM is roughly 12-16 kHz - or even 20 kHz
> depending on which part of the RF spectrum your working.

Granted but the demod is working all the way up to 100KHz bandwidth or 20kHz 
mod, the paramters change as I change the  the counters.
> 
> The Power Squelch may not work on the hackrf - I tried it awhile back
> and I couldn't get it to work. But things have changed since then so
> your mileage may vary.

Yes it does work for me.
> 
> The only parameter you may be able to change reliably using a runtime
> slider on the hackrf may be the center and offset frequencies - provided
> the offset frequency is within the center frequency +- sampling rate/2.
> 
> I did play with sliders on the frequency and sampling rate but I had
> trouble - and since I didn't need it - I didn't pursue it. That was a
> couple of years ago so thing may have changed. And if I recall correctly
> it was changing the runtime sampling rate which gave me trouble.
> 
> You should post your hackrf questions on the
> 
>   address@hidden

Will do.

> 
> > I am using it with hackrf one, to which I will have several questions
> > about
> > but will leave that to a later post.
> > I am lucky in that I have things like a spectrum analyzer and radio test
> > set to work things through with.  I am slowly working through the
> > tutorials and a book called Practical Signal processing, perhaps my age
> > but finding it hard going especially when it comes to Python, cmake, and
> > some of the mathematics!
> > 
> > Anyway if anyone can let me know why I get the results I do I would
> > appreciate it.
> > OS is SUSE Leap 42.3, GNU radio is 3.7.11, just in case that makes a
> > difference.
> > Cheers
> > Adrian


One of the next steps will be to get the dsd blocked installed if I figure that 
out, one of the local repeaters is either analogue or digital I believe.

Thanks

Adrian

Narrow_band_QT_2.grc.png
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Narrow_band_QT.grc
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