Scanning the 2M Ham band

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VE9DAN
Posts: 15
Joined: Tue Jul 31, 2018 12:08 pm

Scanning the 2M Ham band

Postby VE9DAN » Fri Mar 15, 2019 4:28 pm

I tried to set up a Range scan for 2M, but failed.
Has anyone else done it? What are your settings?

I am using Custom Preset 1, 144 thru 148, with a Step of 5k.

This is great fun.
Last edited by VE9DAN on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Tech_Support
Posts: 471
Joined: Mon Jun 01, 2015 7:00 pm

Re: Scanning the 2M Ham band

Postby Tech_Support » Fri Mar 15, 2019 5:12 pm

Hello VE9DAN,
You don't say what your noise floor or your threshold setting is. The only correct way to measure the noise floor is via the power meter when the VFO is placed in a quiet area of the band. Also, don't forget that you need set up your demodulator mode and bandwidth before starting the scan or trying to measure the noise floor. You should avoid setting a step size that is less than the demodulator bandwidth.

Sincerely

Tech_Support

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VE9DAN
Posts: 15
Joined: Tue Jul 31, 2018 12:08 pm

Re: Scanning the 2M Ham band

Postby VE9DAN » Sat Mar 16, 2019 10:23 am

I got it working ... sweet.
The program works fine ... the Operator does not.
Last edited by VE9DAN on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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hfsdpk11
Posts: 34
Joined: Mon May 01, 2017 5:00 pm

Re: Scanning the 2M Ham band

Postby hfsdpk11 » Sun Mar 17, 2019 6:19 pm

I'm having problems as well in trying to scan anything in the FM/VHF band. Tried a freshly-booted instance and it works ok on the AM preset. Then selected the AIRBAND preset and SDRUno crashed. Re-launched SDRU and tried to set up a custom preset with:

Main decimation = 1 (SR = 2000000, IFBW = 1.536 MHz. as fixed values in LIF mode)
Low = 146500000
High = 147500000
Step = 5000
Threshold = -60
Power meter = -92
The other scan settings don't make any difference when set one way or the other,

On starting the scan, VRX0 jumps to 147225000, scanner jumps to 147975000 and hangs there. Why would it go out of the user-defined scan upper limit like that? I cannot step manually to the next frequency nor will it restart after doing a Scan Stop, then Start. It doesn't matter what the VRX0 frequency is prior to starting scan. VRX0 can be 146525000 and it still will jump to 147225000 and scanner will stick at 147975000.

Regarding Tech Support's suggestion not to have a step size less than demod BW, why should that be significant? If I want the sweep to nudge through the demod BW, that shouldn't be a restriction. Looks like a bug to me. Even if I follow the recommendation, it doesn't change the behaviour as described above.

In general, I find the sweep function to be a tantalising disappointment, i.e. it's there but it doesn't work. Also, I'd say the approach is less than desireable where only VRX0 is available for scanning. The problem is that with limiting scanning to VRX0, the LO will always be on top of the scan CF in ZIF mode, thus the apparent "kluge" to force the receiver into LIF mode. Quite frankly, I was hoping that scanning would be a VRX function, not a Main function. That way I could set VRX0 wherever to lock the LO out of the band of interest and scan the VRXn wherever I want and in ZIF mode.

My 2c

Hugo
VE3KTN

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sdrplay
Posts: 919
Joined: Wed Jan 07, 2015 7:58 am

Re: Scanning the 2M Ham band

Postby sdrplay » Sun Mar 17, 2019 9:23 pm

There's a number of things to say about the scanner...

The scanner first performs a DFT (discrete fourier transform) on 1.5 MHz of spectrum at a time. This is crucial for the speed of the scanner. If your total span to be scanned is less than 1.5 MHz, then the LO will never change and could give the impression that it's not doing anything if you don't have signals greater than the threshold. During the DFT, the bins with signals in that are notionally above the threshold will then be sent on to the 2nd part of the scanner. This part goes to each VFO that has been identified in the DFT scan to check if the signal is really above the threshold and is still there.

If it is then it will be demodulated as per the settings (i.e. hold time and/or wait on signal)

If the step size is smaller than the demodulation bandwidth then you are likely to get multiple hits for the same signal as the power measurement is done in the demodulation bandwidth.

It's also worth pointing out that you shouldn't eyeball the threshold in the SP1 display to get a threshold value. Select a quite place in the scan range, click on it and see what the power measurement says (as this is also done in the demodulation bandwidth), then add say 10 dB or a suitable value for the sort of SNR you expect to see for the signals you are interested in.

If you are having problems configuring the scanner, I would recommend that you raise a ticket and if possible show a video demonstrating the problem and screenshots showing how you have the scanner configured as well as the rest of SDRuno would also be useful.

Hope that helps,

Best regards,

Andy

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glovisol
Posts: 579
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Scanning the 2M Ham band

Postby glovisol » Mon Mar 18, 2019 3:14 pm

Hi Hugo,

Forgive me for this (perhaps stupid & obvious question...) did you switch the MW/FM notch filter IN when attempting to scan the 2 m band? In my experience the Scanner works faultlessly....so there must be something obviously wrong on your side.

Cheers,

glovisol

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VE9DAN
Posts: 15
Joined: Tue Jul 31, 2018 12:08 pm

Re: Scanning the 2M Ham band

Postby VE9DAN » Tue Mar 19, 2019 4:56 pm

Hugo ...

Your -60 threshold setting seems pretty high. You will miss signals I would think.
I run my threshold anywhere from -90 (HF) to -110 (VHF).
I like scanning the Aero frequencies for Gander, NFLD, New York, and Santa Maria.

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hfsdpk11
Posts: 34
Joined: Mon May 01, 2017 5:00 pm

Re: Scanning the 2M Ham band

Postby hfsdpk11 » Sun Mar 24, 2019 6:17 pm

Thanks Andy, and to all who replied to my previous post. I haven't had much chance to experiment further with the scanner, but to answer a few questions put to me:

- OK, I get it that there's a block DFT done on the available IFBW, so I take it the scanner window will seem to be stuck while it's actually actively waiting for something to break the threshold, but if I remember from the last time I looked, there's no indicator like "scanning" or "waiting" in the scanner window - only the (out of band) frequency. As a question, and due to something I re-discovered while checking out something else, should LO Lock be enabled or disabled when scanning?

- I've tried with MW/FM notch enabled and disabled. Doesn't make any difference other than to slightly shift the noise floor, as expected, in the amateur 2m band. It doesn't have any obvious effect on the operation of scanner.

- Yes, the threshold of -60 dBm. seems high but I set it there purposely to see what Scanner does while it's supposedly scanning. In FM mode, it jumps to an out of band freq. and sits there without any supplementary info to say whether it's scanning, sitting on a signal, or what. I would have thought at least, that if scanner is active and waiting for a threshold break that the indicated frequency would be at centre of IFBW or the last freq that broke threshold.

- It appears to me that setting the threshold line in FM mode isn't working right. Setting the threshold line seems to be correct in AM modes (AM, USB, LSB) but not in NBFM. I need to look into this more carefully before declaring one way or the other.

Bottom line: I can display a 2m spectrum, select a scan width of 146500000 to 147500000, step size of 15kHz with a FMBW of 10 kHz. and start running the scan with no signals in the desired passband and threshold line set 10 dB. above the indicated noise floor. In-band FM signals that appear and whose peaks touch the displayed threshold line do not trigger scan to that frequency, regardless of what it may be.

That's my story, so far.

Hugo.
VE3KTN.

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