Experimental Baofeng RD-5R version

[do1jml]

I installed the firmware version dated 19/1/2020 on the GD77 and on the RD-5R. I measured the UHF output level on a dummy load with a diamond SX-600 in PEP mode. There is not other difference between the two measurements other than the GD-77 needs a SMA gender changer, as the antenna plug is different between the two devices. So: everything identical up to the antenna plug.

These are the results:

Code: Select all

Ref level		0,5	1	2	3	4	5
GD77 FM			0,3	0,5	1,1	2	2,9	3,9
RD5R FM			0,05	0,5	1,1	1,9	2,5	3,6
GD77 DMR		0,3	0,5	1	1,75	2,3	3
RD5R DMR		0	0,1	0,5	1	1,1	1,5

I am not particularly worried about the FM levels being smaller than they should be. There are losses in the cable, I did not calibrate the meter, the battery was not 100 full (about 70% on both), etc... I am not particularly worried about the GD77 DMR levels being a bit different than the GD77 FM levels, the power meter is not designed for digital signals, even if it does not appear to work too badly. I am also not very worried about very small levels being all over the place, as you said the firmware can only do so much.

But I feel concerned that the RD5R DMR levels are half of the GD77 DMR levels. How can I help you addressing this problem?

[VK3KYY]

I have a contact who works in a facility with lots of good test equipment.

He has a RD5R, so I will ask him to do some tests, and hopefully he will be able to give me some data about the possible cause of this problem you are experiencing.

[do1jml]

I have a contact who works in a facility with lots of good test equipment.

He has a RD5R, so I will ask him to do some tests, and hopefully he will be able to give me some data about the possible cause of this problem you are experiencing.

Great, thanks!

[G4EML]

Hi Roger,

I would suggest looking at the output amplitude envelope with a diode detector or a fast scope. It sounds to me as if the RD5R is not controlling the output power fast enough and doesn't like the 30ms bursts. The bursts could be very distorted if the power rise time is slow.

Colin.

[VK3KYY]

Hi Roger,

I would suggest looking at the output amplitude envelope with a diode detector or a fast scope. It sounds to me as if the RD5R is not controlling the output power fast enough and doesn't like the 30ms bursts. The bursts could be very distorted if the power rise time is slow.

Colin.

Hi Colin

Yes. I agree, that's probably what the problem is.

The radio was originally designed to do Tier 1 only, which doesn't pulse the output RF.
There are few things which get pulsed.

The PA master drive
The PA drive level (from the MK22 DAC voltage)
The antenna switch
The AT1846S Tx

Possibly they do something like not turning off the PA drive and DAC during the entire DMR Tx.
Or possibly leave the antenna switching circuit in Tx the entire time.
This will result in dirty RF, but Jason VK7ZJA has spectrum plots of this radio, which I presumed were taken when it was set to FM, and the spectral output was not very clean.

[VK3KYY]

Colin

I have a DSO with 350MHz bandwidth.

So one option may be to connect and antenna to it, and then transmit on a GD77 and a RD5R on 2m.
The scope may be fast enough to give an idea of the pulse shape.

I've also emailed someone who works somewhere with some specialist test equipment, which he may be able to look at this.
However, I know he is usually busy, and it could take some time, before his workload gives him some time to hook-up his RD5R to their test equipment.

I guess I could also ask Jason VK7ZJA, but I think is is busy doing things on other non-OpenGD77 radios

[G4EML]

If you were to run the radio on VHF you should be able to see the envelope on your scope. Probably just a loop of wire around the antenna would be enough.

If you first test it on FM it will give you a reference level and then compare that with the pulsed RF during DMR. You should see clean square pulses of 30ms going to the same amplitude as the FM did.

I agree the original firmware might not have been pulsing everything.

Colin.

[VK3KYY]

I've not had time to investigate this today, because some of the changes I made to the DMR AMBE audio buffering had an unintended consequence to Hotspot mode, which screwed up the audio, and I've spent all day tracking down some of the problems.

Unfortunately there are still some problems with Hotspot mode, which I'll need to look at, so its unlikely I'll have time to look at this problem for a while.

[do1jml]

I would suggest looking at the output amplitude envelope with a diode detector or a fast scope. It sounds to me as if the RD5R is not controlling the output power fast enough and doesn't like the 30ms bursts. The bursts could be very distorted if the power rise time is slow.

How would the original firmware do it, then?

[G4EML]

As Roger suggested, the original firmware may not pulse everything as OpenGD77 does. It may leave the PA powered all the time.
We know that the RD5R is a very low cost design, they may have done some strange things to get it to work.

Colin.