DCS option

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SQ7PTE
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DCS option

Post by SQ7PTE » Thu Nov 21, 2019 9:24 am

Is it possible to run the DTMF option
I see the CTCSS options and can I change and will the DTMF option be active one day?
Piotr SQ7PTE :roll:

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SQ7PTE
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Re: DCS option

Post by SQ7PTE » Thu Nov 21, 2019 1:17 pm

Roger.
I mean DCS (Digital Coded Squelch)
Piotr SQ7PTE :roll:

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KU4ZD
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Re: DCS option

Post by KU4ZD » Thu Nov 21, 2019 2:45 pm

DCS or DPL ?
Mike KU4ZD

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Re: DCS option

Post by KC7RBW » Thu Nov 21, 2019 3:08 pm

Are DCS and DPL any different apart from Motorola branding?

G4EML
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Re: DCS option

Post by G4EML » Thu Nov 21, 2019 4:32 pm

DCS and DPL are the same thing.
The AT1846S chip does support DCS but the documentation is poor and we don't currently know exactly how to control it.
I hope it can be supported eventually but as DCS is not very commonly used in Amateur systems it is probably quite low down the list of things to do.

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Re: DCS option

Post by VK3KYY » Thu Nov 21, 2019 8:14 pm

I can capture traffic to the AT1846 and log it using the debugger

But I don’t have time to investigate this at the moment

N2GXT
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DCS

Post by N2GXT » Mon Jan 20, 2020 10:39 am

I can not get the DCS to work on receive or transmit. It will not open any of the DCS repeaters. Anyone know a fix

G4EML
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Re: DCS

Post by G4EML » Mon Jan 20, 2020 10:52 am

DCS is not implemented on the OpenGD77 firmware.
This may be added at a later date but is not a high priority.

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Re: DCS option

Post by KC7RBW » Wed Mar 11, 2020 3:25 am

I started to look at what it would take to support DCS. It seems the AT1846S is expecting the Golay{23,12} encoding of the octal DCS code, which is a bit weird.
For example: When tx or rx Cdcss023
4bH=0x0076 and 4cH=0x3813
But whatever, we can compute that. The 23bit Golay encoding (using the 0xC75 polynomial) of the octal 023, with the octal 4 prefix required by DCS encoding (so octal 4023) is 0x763813 as shown in the documentation.

Since there are only 83 standard DCS codes I think I'll precompute them which will occupy about 249 bytes and the lookup table will be quick.

No estimate on when I'll have a PR ready since I'm mucking around with things I don't yet understand. I'll make sure it looks completely correct to me and it's tested before I post it.

I'm curious if people actually use DCS. I found maybe 3 repeaters in my area that claim to use it (in the coordination database) but when I dug deeper on one of them I found it had been switched to CTCSS.

One of the reasons it seems to be unpopular is that on TX you have to figure out if the signal needs to be inverted for the repeater to hear you, and on RX you need to figure out the same thing. There doesn't seem to be a clear standard on the inversion, so if you have a mixed system (that is, not all Motorola) you might have to flip it on TX, RX, or both to get it working. Messy stuff.

The reason it still lives seems to be that Yaesu wants you to use DCS when using a Fusion repeater in mixed Digital / Analog mode for some reason, and they sold those DR1X repeaters for so cheap a while back that everyone is using them (usually with an MMDVM module in them so they can run D-STAR or DMR instead).

Correct me if I got any of the above wrong, I'm eager to learn.

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Re: DCS option

Post by VK3KYY » Wed Mar 11, 2020 3:55 am

In case it helps there are Golay functions in both the "dmr" folder (which is acually the hotspot DMR support folder) and also in the AMBE decoding / encoding functions as the AMBE binary sections don't seem to include all the Goloay processing that is required.

We may have some duplication at the moment with those Golay functions, but I'm not sure, as I've not had time to investigate if the are the same encoding or not. But as there are multiple types of Golay, I presumed the encoding may be different in both cases.
And your Golay requirements may be different again.


Also. On the schematic for the GD-77, it shows a LM321 configured as a band pass filter, with input connected to the AT-1846 AF output, and its output connected to pin 18 of the MK22 (ADC0_DP0/ADC1_DP3) labelled DTMF DET

I don't know whether this is relevant to DSC if it use.

This input is an ADC pin, but we don't read it in the firmware.

Originally there was some boilerplate code that was reading 4 ADC's all the time, just to read the battery level, but I took out the code that read the other pins because the firmware was not using that data.

However, it looks like we may have to sample the other ADCs in order to support some features like VOX

The following signals seem to be connected to the ADC's

VOTAGE ----- MK22 14 (ADC0_DP1)
RDA_SQL ----- MK22 16 (ADC1_DP1/ADC0_DP2)
DTMF DET ----- MK22 18 (ADC0_DP0/ADC1_DP3)
VOX ----- MK22 20 (ADC1_DP0/ADC0_DP3)

The VOX signal is clamped by a device (ISS372) which appears to be some back to back diodes, there also appears to be a low pass filter on this signal with an electrolytic capacitor to smooth the input. But I don't know the details of this filter (and its irrelevant to DCS)

For DCS, I doubt that they would be using the MK22 to demodulate the DCS, its more likely that the AT-1846 would be doing this, if it has that capability. The DTMF DET line is probably just used to signal to the MK22 that it needs to setup and read DTMF from the AT-1846

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