[Solved] Pi-Star cannot receive OpenGD77's signal

BG9EGA
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[Solved] Pi-Star cannot receive OpenGD77's signal

Post by BG9EGA » Tue Jul 28, 2020 6:01 am

Hello,
My Radio is TYT MD760(As same as Radioddity GD-77). Used D20200628 OpenGD77 firmware.
The Simplex board is MMDVM_HS Hat for the Raspberry Pi.

When I pushing the PTT, The Radio is trying to connect the simplex board. But the simplex board does not respond, and the LED light is not on.
I used another MD380 Radio and the simplex board. They work well together.
The sending and receiving between MD760 and MD380 is also normal.
Maybe the problem is on the TX of MD760.

I checked the configuration and they are correct.
Use some old firmware of OpenGD77, but the problem remains.
Try to use someone else’s calibration, not good.

Yang/BG9EGA
Last edited by BG9EGA on Fri Jul 31, 2020 12:56 am, edited 1 time in total.

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YT5HOK
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Location: Belgrade, KN04FR

Re: Pi-Star cannot receive OpenGD77's signal

Post by YT5HOK » Tue Jul 28, 2020 7:29 am

You should use mmdvmcal to calibrate your hotspot and/or use SDR to calibrate both, hotspot and transceiver.

Here are guides on mentioned subjects:

K9NPX Hotspot Offset Calibration

N5AMD Tune your MMDVM repeater with an SDR

Cheers!

BG9EGA
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Joined: Tue Jul 28, 2020 3:29 am
Location: Shaanxi, China

Re: Pi-Star cannot receive OpenGD77's signal

Post by BG9EGA » Tue Jul 28, 2020 5:29 pm

Hi Marko
Thank you for your help!

I uesd “pistar-mmdvmcal”, and calibrated my Pi_Star(RXOffset 600). It can receive calls from MD760.
But now it cannot receive MD380's calls.
Restore configuration to 0(RXOffset 0 and TXOffset 0), MD380 Works very good.
So, the frequency of MD380 and the simplex board is accurate. The problem is in MD760.

I found that OpenGD77 CPS and official CPS has calibration function.
But there are so many options and numbers. I will not use this feature. I don't know what to do.
How to correct the calibration of MD760?

Thanks!
Last edited by BG9EGA on Thu Jul 30, 2020 3:46 am, edited 1 time in total.

VK3KYY
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Re: Pi-Star cannot receive OpenGD77's signal

Post by VK3KYY » Wed Jul 29, 2020 1:58 am

BG9EGA wrote:
Tue Jul 28, 2020 5:29 pm
Hi Marko
Thank you for your help!

I uesd “pistar-mmdvmcal”, and calibrated my Pi_Star(RXOffset 600). It can receive calls from MD760.
But now it cannot receive MD380's calls.
Restore configuration to 0(RXOffset 0 and TXOffset 0), MD380 Works very good.
So, the frequency of MD380 and the simplex board is accurate. The problem is in MD760.

I found that OpenGD77 CPS and official CPS has calibration function.
But there are so many options and numbers. I will not use this feature. I don't know what to do.
How to correct the calibration of MD760?

Thinks!
This is normal.

I can't use my MD-380 and GD-77 on the same hotspot, even running the official firmware on both radios, also my Baofeng DM-1801 doesn't work with any of my hotspots unless I significantly change the settings in the hotspot.

You could try adjusting the calibration, Reference Oscillator frequency in the GD-77 or the MD-380 to make sure they are both on exactly the same frequency, but the frequency is not the only difference, and often its the 4FSK modulation / deviation level which is different between these 2 radios, and you may need to adjust both radios to produce the same level of modulation.
I've tried to make these adjustments on my GD-77 and DM-1801 radios and still can't get them to share a hotspot.

However my crappy RD-5R does seem to co-exist with the GD-77 on both my simplex and duplex hotspots

The thing to bear in mind, is that the RF chip (ADF7021) used in the hotspots, are not intended for streamed digital audio operation.
This cheap chip intended for short range telemetry busts.

Hotspots always have to be manually adjusted to receive transmissions from DMR radios, and getting some hotspots to work with completely different radios is a challenge and is not always possible.

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kd2lh
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Re: Pi-Star cannot receive OpenGD77's signal

Post by kd2lh » Wed Jul 29, 2020 10:27 pm

Note that the Pi-Star running on "JumboSpot" hardware (with one of the radio "hat" boards on a Raspberry Pi) have a Software defined Radio chip without Automatic Frequency Control implemented.

This means that the fine adjustment of the center of the radio's reception frequency is necessary, and the Chinese made radios often vary in calibration by several hundred cycles.

Using a GD-77 as a hotspot's receive and transmit radio (directly connected to a Raspberry Pi by USB cable) helps to solve this problem.

Marc

BG9EGA
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Location: Shaanxi, China

Re: Pi-Star cannot receive OpenGD77's signal

Post by BG9EGA » Thu Jul 30, 2020 2:10 am

VK3KYY wrote:
Wed Jul 29, 2020 1:58 am
This is normal.

I can't use my MD-380 and GD-77 on the same hotspot, even running the official firmware on both radios, also my Baofeng DM-1801 doesn't work with any of my hotspots unless I significantly change the settings in the hotspot.

You could try adjusting the calibration, Reference Oscillator frequency in the GD-77 or the MD-380 to make sure they are both on exactly the same frequency, but the frequency is not the only difference, and often its the 4FSK modulation / deviation level which is different between these 2 radios, and you may need to adjust both radios to produce the same level of modulation.
I've tried to make these adjustments on my GD-77 and DM-1801 radios and still can't get them to share a hotspot.

However my crappy RD-5R does seem to co-exist with the GD-77 on both my simplex and duplex hotspots

The thing to bear in mind, is that the RF chip (ADF7021) used in the hotspots, are not intended for streamed digital audio operation.
This cheap chip intended for short range telemetry busts.

Hotspots always have to be manually adjusted to receive transmissions from DMR radios, and getting some hotspots to work with completely different radios is a challenge and is not always possible.
Hi Roger

I followed your instructions and changed the reference oscillator repeatedly. But the frequency test results did not improve.
As you said the frequency is not the only difference, and often its the 4FSK modulation / deviation level which is different between these 2 radios.
It is difficult to debug the radio. So I have restored the calibration, and bought another hotspot for separate use.
My skills are limited, so I have to study hard.
Although cheap equipment has a lot of trouble, but the process of solving the problem has learned a lot of knowledge and pleasure.
I like your firmware and blog very much.
Thanks!
Last edited by BG9EGA on Thu Jul 30, 2020 3:38 am, edited 1 time in total.

VK3KYY
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Re: Pi-Star cannot receive OpenGD77's signal

Post by VK3KYY » Thu Jul 30, 2020 2:46 am

BG9EGA wrote:
Thu Jul 30, 2020 2:10 am
Hi Roger

I followed your instructions and changed the reference oscillator repeatedly. But the frequency test results did not improve.
As you said the frequency is not the only difference, and often its the 4FSK modulation / deviation level which is different between these 2 radios.
It is difficult to debug the radio. So I have restored the calibration, and bought another hotspot for separate use.
My skills are limited, so I have to study hard.
Although cheap equipment has a lot of trouble, but the process of solving the problem has learned a lot of knowledge and pleasure.
I like your firmware and blog very much.
Thinks!
No worries.

I have the same problem with my radios. Not only when using the OpenGD77 firmware.
I have a separate hotspot I use for my DM-1801.

Also, I recall there are some problems with the MD-380 where the hotspot modulation level also needed to be adjusted so that it would communicate with the MD-380 at all.

Unfortunately because of the nature of the 4FSK modulation used by DMR its very hard to configure multiple radios to be exactly the same.

But, as you say, this hobby is suppose to be about learning etc, so I'm glad that you have expanded your knowledge

73

Roger

BG9EGA
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Re: Pi-Star cannot receive OpenGD77's signal

Post by BG9EGA » Thu Jul 30, 2020 3:34 am

kd2lh wrote:
Wed Jul 29, 2020 10:27 pm
Note that the Pi-Star running on "JumboSpot" hardware (with one of the radio "hat" boards on a Raspberry Pi) have a Software defined Radio chip without Automatic Frequency Control implemented.

This means that the fine adjustment of the center of the radio's reception frequency is necessary, and the Chinese made radios often vary in calibration by several hundred cycles.

Using a GD-77 as a hotspot's receive and transmit radio (directly connected to a Raspberry Pi by USB cable) helps to solve this problem.

Marc
Thanks for reminding!
I calibrated my Pi_Star(RXOffset 600 TXOffset 0). At this time, the radio can be used normally
After that, I uesd “pistar-mmdvmcal” to test Radio's receive. The conclusion is 1300 Offset.:shock:
I did not set the TXOffset of Pi-Star, but Radio can receive normally.
So, the receive of simplex board hotspot is stricter. High requirements for the radio's TX frequency.
Maybe using a radio as a hotspot, receive should be good.

I tested Hotspot and BlueDV for OpenGD77. perfectly worked!
But it’s a bit big, I prefer Raspberry Pi Zero + Simplex Board. :)

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kd2lh
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Re: [Solved] Pi-Star cannot receive OpenGD77's signal

Post by kd2lh » Sat Aug 01, 2020 9:09 pm

These are all a tradeoff. The JumboSpot (simplex and even duplex versions) are very very compact and remarkable pieces of technology.

If you read the details of the AF7021 SDR radio receive/transmit chip you'll find that it does have an AFC implementation available.

https://www.analog.com/en/products/adf7021.html#

Perhaps the processing load on the STM32 Arduino processor doesn't allow implementing this feature on such low cost hardware. I haven't looked into the firmware, so don't really know the reason.

Also, the stability of these radios is completely dependent upon the quality of the reference oscillator. The better Chinese boards import this oscillator from a US manufacturer source.

Marc

G4EML
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Re: [Solved] Pi-Star cannot receive OpenGD77's signal

Post by G4EML » Sun Aug 02, 2020 10:02 am

The internal AFC of the ADF7021 does not work correctly with pulsed TDMA signals as used by DMR. In fact the chip struggles to lock on these signals with or without AFC. Hence the need to fine tune the frequency to minimise the errors.

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