Scan speed versus sensitivity

VK3KYY
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Re: Scan speed versus sensitivity

Post by VK3KYY » Fri Mar 26, 2021 9:50 pm

I can use Scan speed: in cps , but I think the units of 'cps' would be confusing as people may confuse this with the CPS software

I prefer not to use an arbitrary scan speed list like 1 to 10 as it requires to operator to read the userguide to know what speeds the numbers relate to.

I guess we could use c/s for the unit, as perhaps this is the correct technical description of the units.

Using channels per second, I could use steps of 5 starting with 35 per second.
I.e. 35,30,25,20,15,10,5,1

But there is a loss in granularity over the millisecond per channel value, unless I do it in steps of 1 or 2, but the change of rate from 35 to 34 is a lot less than from 10 to 9


It seems to be the main problem is the limited text to describe this value and other languages will have to translate and abbreviate this as well

If we go for abbreviations, we could use Scan samp.:30ms

As this should be fairly clear that its his long it samples for

But perhaps Sample is a computer based term and not ideal for radio,

Perhaps Scan Rx: 30ms

Edit

I've just realised that using non SI units e.g. 'cps' is problematic, as the units would need to be translated as well.

And also, its not just Channels Per Second, this value also relates to the VFO, where there aren't any channels.

So for scan speed, in steps per second, the value could not easily have any units

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Re: Scan speed versus sensitivity

Post by VK3KYY » Sat Mar 27, 2021 12:19 am

Well, the plot thickens.

I changed the code to allow the number of steps per second to be used instead of the dwell / sample time, but when I did some timing tests the values were not what I expected.

The problem is that is a set-up time associated with changing channel and also updating the display, is not insignificant, so that when I used 1000 / STEPS_PER_SECOND, is used as the Rx dwell time, and does not include the overhead of everything else that needs to happen when the channel is changed.

So when I set a value of 50 channels per second, ie sampling for 20ms, the actual speed was about 22 channels per second, or 45 ms per step

At the moment, I'm not sure what is taking most pf the additional 25 milliseconds. I think its most likely to be the EEPROM, as the details of the channel including its name and frequency and CTCSS settings etc, need to be loaded and the EEPROM is not super fast.

For best scan speed, the scan functionality needs to be changed so that the next channel while the current channel is being sampled.

So, I'll need to think a bit about how best to approach this problem

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W1AEX
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Re: Scan speed versus sensitivity

Post by W1AEX » Sat Mar 27, 2021 11:28 pm

Hi Roger,

Just a quick comment to say that the present implementation works beautifully. The 30ms increments are easy to understand and they provide a lot of range in the settings for the user to experiment with. Maybe it's not necessary to change what you have already created?

Thanks, Rob W1AEX

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Re: Scan speed versus sensitivity

Post by VK3KYY » Sun Mar 28, 2021 2:06 am

W1AEX wrote:
Sat Mar 27, 2021 11:28 pm
Hi Roger,

Just a quick comment to say that the present implementation works beautifully. The 30ms increments are easy to understand and they provide a lot of range in the settings for the user to experiment with. Maybe it's not necessary to change what you have already created?

Thanks, Rob W1AEX
Thanks Rob.

In theory the channels per second sounds good, but because of time that the radio takes to configure the hardware after the channel is changed, calculating the time for spend listening on each channel gets quite complicated.

i.e If someone sets the speed to e.g. 20 channels per second, and the radio ends up only doing 18 channels or perhaps doing 22 channels, I'm sure we'd get a bug report saying the scan speed value is not correct.

Also for DMR Simplex channels, the minimum dwell time is automatically configured to 60 milliseconds, because the Rx signal is only active for 30ms every 60ms, which effectively make any control of channels per second virtually impossible.


One interesting benefit of looking at the scan speed is that Daniel found some duplicate code in the scan function, which was slightly slowing the scan down, Daniel has sent me a fix for this.

I've also noticed that the time to setup the Rx hardware seems a lot longer than I expect it to be. So I think potentially there is another bug in the scan function which is either slowing the scan down or making the sensitivity worse (as sensitivity related to dwell time)

So, I'm going to investigate if there is something else wrong in the code

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Re: Scan speed versus sensitivity

Post by VK3KYY » Sun Mar 28, 2021 10:37 pm

Daniel and I have been looking at the scan function and Daniel has found and fixed several bugs

Additionally I have investigated the unexplained dead time during the scanning process where the Rx was not listening, and I have reduced this dead time by around 75%

So that the scan speed will be approximately 30% faster when the 30ms scan step time is selected.
Larger scan step times, were progressively less impacted by the dead time, because the dead time was a fixed value of up to 20 milliseconds

I think there are still some small improvements which can be made to the scan speed, but these will only make a marginal difference to the scan speed, and I have not had time to work on them yet.

https://github.com/rogerclarkmelbourne/ ... est_v3.zip

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Re: Scan speed versus sensitivity

Post by m1dyp » Mon Mar 29, 2021 5:14 am

thank you

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W1AEX
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Re: Scan speed versus sensitivity

Post by W1AEX » Mon Mar 29, 2021 9:31 pm

Hi Roger,

I loaded the scan_speed_test_v3 firmware (3-39-2021) into both GD77s and it works fine for me with both radios. I'll do some scan tests here with both radios at 30ms, 60ms, 90ms and 120ms to see what differences in scanning behavior might appear. I did notice at 30ms that when I scan my DMR simplex zone (5 frequencies installed) that both radios occasionally skip by and then catch the busy channel on the next pass. I'll take a look to see if that behavior stops at one of the higher settings. Thanks to you and Daniel for all the work on this.

73, Rob W1AEX

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Re: Scan speed versus sensitivity

Post by VK3KYY » Mon Mar 29, 2021 9:49 pm

Thanks Rob

In my experience, its always occasionally skipped DMR signals, when the scan speed was not adjustable and hence the value was set to 30 milliseconds, and for DMR repeater signals.

I don't think the recent changes have made any difference to this.

I've not looked in detail at why the scan occasionally misses a DMR signal, yet latches onto it in the next pass, and I also don't know whether this is also true for analog signals.

I may change the granularity of the scan dwell setting from 30 milliseconds to 5 milliseconds, as this would allow people to do some experimentation to find the optimum value for the minimum setting.

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Re: Scan speed versus sensitivity

Post by DJ0HF » Tue Mar 30, 2021 7:35 am

Hi Roger,

you have probably already noticed but the scan step voicing in v3 doesn't voice scan step and says for example 30dmb instead of 30 milli-seconds.

73,
Ian
DJ0HF/G3ULO

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Re: Scan speed versus sensitivity

Post by VK3KYY » Tue Mar 30, 2021 8:50 am

DJ0HF wrote:
Tue Mar 30, 2021 7:35 am
Hi Roger,

you have probably already noticed but the scan step voicing in v3 doesn't voice scan step and says for example 30dmb instead of 30 milli-seconds.

73,
Ian
DJ0HF/G3ULO
Thanks.

I know ;-)

Daniel found we are not using several of the existing prompts including dB, so we will need to re-use those slots for any new words, as we are close to the limit of the total number of prompts.
And I need to add a new entry for what will be the "Scan dwell" time.

I've actually been looking at the VP files today, to make these 2 changes to all the supported languages, but I noticed that over half the VP translated languages don't have anyone regularly providing translations, so I've decided to use Google translations for those languages as its probably better, in most cases, than no translations.

Then if people want to provide me with updated texts for the VP I will then update the VP.

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