DM-1701 TX CC issues

[G4EML]

The reason people have to calibrate their hotspots is down to a basic design flaw in nearly all of them. They all use a single chip RF transceiver , the ADF7021. This chip has Automatic Frequency Control which is designed to lock the receiver onto the incoming signal. This works fine with constant carrier systems such as DSTAR and C4FM but it really struggles with the 30 ms pulsed signal of DMR. The AFC is unable to lock quickly enough onto the short bursts and so the decoding is poor or non existent.

The 'work around' that was developed by the early hotspot designers is to fine tune the ADF7021 receiver frequency so that the AFC does not need to adjust anything and does not distort the signal, however this is a very critical adjustment and often even a tiny change of a few tens of hertz is enough to go from perfect decoding to nothing at all. The precise adjustment also drifts with time and temperature.

The DMR specification itself is quite tolerant of frequency errors and the concept of having to adjust frequency to such fine limits never existed before the introduction of the ADF7021 hotspots. Plus or minus 400Hz is allowed in the ETSI spec. and most radios will still work with greater than this. Individual radios will always vary by a few hundred Hertz in their exact frequency, which is why it is often difficult to adjust a hotspot to work with multiple radios.

Incidentally this is one of the main benefits of using an OpenGD77 radio as a hotspot. Because it is a radio designed to work with DMR signals the problems associated with the ADF7021 do not exist. OpenGD77 hotspots are much more tolerant of frequency and should not require any special calibration.

Colin G4EML

[K7TLU]

Thank you for the explanation I really to appreciate you sharing your knowledge. That is fascinating and makes very logical sense.

I may look into using an OpenGD77 radio as a hotspot as I have not been very satisfied with my mmvdm hat, its a very picky little device that's for sure.

[VK3KYY]

.... as I have not been very satisfied with my mmvdm hat, its a very picky little device that's for sure.

Did you do the frequency calibration on the hotspot ?
I thought it was pretty much mandatory that you do this, otherwise the don't work

I'm sure there are loads of videos on YouTube about how to do it.

Changing the hotspot calibration +/200Hz makes a huge difference to whether it works or not, or the BER.
Most people adjust their hotspot in about 100Hz increments to get the best BER

[K7TLU]

Apparently I had a healthy helping of beginners luck, because I never had to perform a frequency calibration on my hotspot for use with the Anytone, once the software was configured properly and I had a working codeplug, it just worked.

This DM-1701 is only my second DMR radio not counting the MMDVM hat, so I am still finding my feet in the digital radio world. I never really liked the Anytone form factor and menu system. It never felt good in the hand and always felt clunky making any adjustments on the radio so did not get that deep into DMR prior. So far I am really really liking the OpenGD77 firmware/CPS, it is such a vast improvement over the Anytone, at least IMHO.

You were completely correct, tons of videos on the calibration process. After I get an opportunity to calibrate my MMDVM I will be sure to update this thread with the results.

Thank you!!!!
73s

[VK3KYY]

Apparently I had a healthy helping of beginners luck, because I never had to perform a frequency calibration on my hotspot for use with the Anytone, once the software was configured properly and I had a working codeplug, it just worked.

This DM-1701 is only my second DMR radio not counting the MMDVM hat, so I am still finding my feet in the digital radio world. I never really liked the Anytone form factor and menu system. It never felt good in the hand and always felt clunky making any adjustments on the radio so did not get that deep into DMR prior. So far I am really really liking the OpenGD77 firmware/CPS, it is such a vast improvement over the Anytone, at least IMHO.

You were completely correct, tons of videos on the calibration process. After I get an opportunity to calibrate my MMDVM I will be sure to update this thread with the results.

Thank you!!!!
73s

OK. Calibrate the hotspot to match Anytone

Then use the calibration screen in the OpenGD77 to calibrate the DM-1701 to the same frequency

Do you have a SDR dongle etc, or anything else that can show a spectrum plot.

Or just buy a SDR dongle the old RTL SDR ones are dirt cheap and work fine

The you and transmit FM (no audio) on your Anytone and compare the central freq with your DM-1701

[K7TLU]

Reporting Back: Both radios are now working with my hotspot, the mmdvm needed a -300 Hz adjustment.

I'm not sure why but the Anytone is more tolerant of a frequency mismatch between the hotspot and the radio. Using an SDR I was able to see that the 1701 was transmitting bang on frequency while the hotspot was slightly over frequency. From there I started up the calibration for the mmdvm and found that the 1701 would decode from an adjustment of -50 to -600, and the anytone would decode for about another 100 Hz deviation in either direction after the 1701 would stop decoding.

I should also note that on my parrot testing the sound quality has also now improved as well.

Thank you everyone for helping this newb find his feet

73s

[VK3KYY]

The Anytone has a better Rx. The TRx chip in the Dm1701 literally costs only $1 and was never designed to receive 4FSK modulation

I'm just to surprised the Anytone works better