HAMDig

Here is another Tytera MD-380 observation.

On 2 December, I attended a digital radio service presentation by the well-known service monitor company Cobham/Aeroflex. I brought my 450 MHz MD-380 along.

After the presentation, I asked Mike Fortna of Aeroflex to take a look at the infamous MD-380. He said Tytera had contacted them about developing an Autotest routine for Tytera products, so Mike was interested in seeing the Tytera MD-380's alignment.

Testing was done on 441 MHz Simplex and again on TS1 on the Gunnysack pair with the Cobham/Aeroflex 8800S Digital Radio Test Set. The 4FSK modulation was perfect. Mike had just been explaining that most problems with alignment are revealed on the 4FSK display, but the Tytera was perfect. I asked him to look at the energy in each timeslot. I think this display is called the power profile. The graphic showed timeslot 1 and 2 simultaneously.

What was observed was a non-standard rise time when keying the transmitter. The power in timeslot 1 came up about half of maximum, hung there for a few uS, then went to full power. It was not a nice rounded envelope. It was a stair step. No overshoot was observed. Other than the "stutter" in reaching full output, the waveform was mostly normal. The abnormal condition was likely caused by the "stutter" in rise time. This abnormal condition is RF energy "spilling over" into timeslot 2 in this case. It seemed to appear in timeslot 2 for the same duration as the stutter in the timeslot 1 rise time.

Mike Fortna of Aeroflex found it interesting enough to take a screen shot. He stated it was a better example of a DMR power profile alignment problem than what he was currently using.

The same waveform anomaly occurred on Simplex and Duplex. Rapid keying, de-keying and keying again made no difference in the waveform. I have read that transmitting on both timeslots simultaneously was a "feature." This doesn't seem to be true.

I didn't have time to test on timeslot 2. Testing was rushed because everyone knew that Seattle traffic was building!

Further, more comprehensive testing is required with a greater pool of radios. It would be interesting to test some high-band models as well. Does anyone have an IFR3920 or 8800S with the DMR option?

This only meant to be a verbal description of the graphical representation of an anomaly in my particular MD-380's timeslot power profile. Your mileage may vary, as they say.

Brian, KE0CO

kb9mwr wrote:http://hackaday.com/2016/01/19/shmoocon ... -firmware/

Sorry... The MD380 will not be able to do any other formats beside DMR and Analog because of the C5000 Baseband chip inside. We looked at using that about 2 years ago for the CS7000. Even if you were able to get C5000 chip to do what is needed, how will you get the DSTAR Vocoder in that radio?

Jerry Wanger KK6LFS