Lscott

If it is then this is the brochure for it. https://www.motorolasolutions.com/content/dam/msi/docs/EA_Collaterals/ENGLISH/MOTOTRBO/Portables/DP4000_DataSheet_ENG_lor.pdf

Given how Motorola has entitlement keys you write to a radio to enable various features I just can't see how anyone could make a definitive claim. I have a bunch of Kenwood radios, and a few Motorola's, myself and some look identical. Can't tell them apart without looking at the tags on the back side under the battery pack.

OK. My guess is it was the power transistor that failed. That can happen for several reasons. I listed a few below but it's not all inclusive. 1. It was improperly installed. The screws were not torqued down correctly. Too much, too little or no thermal compound used between the transistor's mounting flange and the heat sink. 2. High SWR on the amplifier output. May not have to exist for very long, monetary, to blow the transistor. 3. High voltage transients on the DC supply. 4. If any kind of "bias" is applied to the transistor it wasn't designed right, or the temperature sensor is not installed VERY close to the transistor. That can cause the transistor to go into thermal runaway which will destroy it in seconds. This applies to bipolar types. FET's are different. 5. The transistor is being used beyond it's published power ratings. One might get away with this so long as the duty cycle is kept low.

What do you mean by "the RF chip"? I only see one small black IC chip on the board. You're not mistaking the large power transistor that's screwed to the heat sink are you?

Any clue as to exactly what failed in the 3 amps you had? If it's the same failure and knowing what it was there might be a fix for it, or avoiding whatever it was that precipitated the failure.

I've attached a section out of the function reference guide for the NX-200/300 series radios for the transparent data mode. You have the NX-5000 series which I assume the functions will be similar. The HT's don't have any hardware flow control so the TNC emulator has to implement some form of software flow control. The mobile radios might have the hardware flow control on the interface port. Transparent Data Mode.pdf

Have you tried doing any data exchange using DMR or one of the other modes? From what I've read using the "narrow", not the "very narrow" mode on NXDN you can get a faster data rate than with DMR, which is limited by the TDMA method used. The Kenwood radios I have include a TTL level serial port that can be configured for data transmission. The radio is used as a modem with the native digital voice mode doing the communication protocol to facilitate the exchange. In the programming software it's configured as either "Transparent" or "Transparent 2" for the protocol. Using the builtin serial port one no longer need a "packet" interface, which is basically a direct connection to the modulator input and discriminator output. Then you had to screw around to get the right signal levels for the frequency shift required. The serial port, and the radio's native digital mode, takes care of all that for you. What I'm looking for is software to emulate a hardware TNC. Just about everything I've found either won't work on the newer version of Windows, or requires DOS and wants to interface to a sound card, which isn't needed using the digital radio. I've been told some had success using D-Rats, but thats aimed more towards D-Star specifically.

Can't see what kind of radio it is, just saw it from the backside. They likely would try to recover any radio they spot. If it's a military grade or commercial it could be a digital type and mostly likely using encryption. They would be interested if the later was the case due to any encryption keys. The radio might have been lost before it could be killed and the keys wiped. Of course the last possibility is it's a "plant" left there hoping it would be recovered. Then it could be traced or used to supply false information to the Ukrainians.

I think I just go back to playing with my D-Star, NXDN and P25 radios.

There are two models of this amp. One is usable for TDMA type radios, DMR mode, whereas the other one isn't. Are people sure it's the AMP-U25 and not the AMP-U25D? Could the amp have been misused by any chance? A high SWR between the amp output and the antenna is likely a good indication the amplifier is generating a high level of harmonics, and other garbage, that's being reflected back to the amplifier. The amp may have been over driven too. Some radios are not well behaved when the power is turned down. I know the old Icom IC-706MKIIG had a nasty habit of spiking up to full power very briefly before dropping down to a lower set power. I have a new AMP-U25D version, haven't used it yet, that is rated for ALL the common digital modes. A comment was made by a poster that a "chip" failed in their amp. I've attached a PDF file, from the FCC, showing the internals of the -U25D version. I'm going to guess it's similar to the -U25. Does anything in the photos look like the part that failed? Internal-Photos AMP-U25D.pdf

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This is the one thing that bugs me, mostly with DMR. That's the multiplicity of networks. I try to program up my radios and every repeater seems like they have to use a different network for linking. If you're lucky the talk group numbers are the same, but not always. Then you have to jump through hoops to link from one network to another if the one you want is on the "other" network. DMR is enough of a pain as it is to program up a radio without the above BS on top of things. Here in Michigan for example a number of local repeaters use the Mi5 network. Dah! https://w8cmn.net/mi5-sites-talkgroups/ And a de-funked network. https://dmrx.net/dmrx-core.html And this is an example of a repeater that's a bit more changeling to program. It uses several different networks and talk groups. http://n8noe.us/DMR/dmr.html

If Kenwood ever started to produce the TH-D74A again in a DMR format they likely couldn't keep them in stock on the shelf. I would be interested in buying one just to get away from the Chinese stuff.

Thanks for the comments. This was something I was curious about.

Here is a question I haven't seen talked about. On many of the commercial grade digital radios they can be operated in analog only, digital only, or in mix mode. The later would have the radio programmed to receive in either analog or digital on a given frequency while automatically detecting which mode is in use and demodulating the signal as necessary. The transmit mode is usually set for either analog or digital exclusively. I don't have any of my radios programmed for mix mode. Other than monitoring a frequency for activity has anyone else found it beneficial?

I'll take your word for it. You have the real world experience to back it up. Was there anything that was, or could be done, to mitigate the interference issues?

Yeah, should get back on topic.

I forgot to mention there are also problems with "clock drift" of the internal oscillators in digital radios and DMR also has to deal with range limitations due to slot timing too. See page 110 section 10.1.4, and page 113 sections 10.2.3.1.2 through 10.2.3.2.3 in the following link. https://www.etsi.org/deliver/etsi_ts/102300_102399/10236101/02.02.01_60/ts_10236101v020201p.pdf

This is encouraging, somewhat back on the thread's topic and people expressing some interesting ideas and opinions. Some of the issues, with at least DMR, is the proliferation of mainly Chinese radios, cheap and not so cheap. The cheap ones tend to give users a poor impression of the mode's performance. The commercial radios are much better, but of course more expensive. IMHO the issue with DMR causing interference to analog users I believe can be traced to poor receiver design and channel separation. For example the common bandwidth quoted for DMR is 6.25KHz "equivalent" which is not the same as a true 6.25KHz signal. DMR is in fact a 12.5KHz signal, and due to TDMA, two voice streams can occupy the channel, that's the equivalent part. Some radios cheap out by using 25KHz IF filters in the radio while limiting the FM deviation to 2.5KHz to meet the FCC's 12.5KHz occupied bandwidth. Locating a adjacent transmitter closely to such a receiver will result in the DMR signal spilling over in to part of the pass band of the affected receiver.

Somebody with far more experience than me would need to VERY carefully write up a petition for submission. I think it's been tried before. I'm guessing any chance of success in rule modifications are those that requires the least work on the part of the FCC and not going overboard on the requested changes. The last part I think is key to the whole thing. Keep it modest and reasonable.

That is a big consideration. The proposal to use the low power channels, 8-14, was an attempt to mitigate the issue. I suspect most GMRS radios don't even include the low power narrow channels, and if they do most users, I suspect, ignore them anyway. This way to side step any FCC objections to new spectrum allocations.

That's very unlikely to happen for several reasons. 1. The Hams will vigorously defend their spectrum from getting "pilfered" by another service. If they did take any spectrum the FCC would likely auction it off for money. 2. It would require some major revisions to the GMRS rules and spectrum management, not to mention mucking up the unified frequency allocations between GMRS and FRS. 3. The primary user of the 70cm is the government. Hams are only secondary users.

Well that's what the FCC had envisioned the service's main use. However as any casual member of this forum sees it has evolved more towards a hobby use. I guess there is nothing wrong with that, but the FCC would be quick to point out that wasn't the original intent. That was mentioned in the initial comments. The purpose of the document is to get people thinking about it and to at least consider what the FCC might realistically consider. Start small and when you gain some ground push a little further. This plays into the topic of this thread. There are a lot of digital modes in use on the Hams bands. While that might be a good thing it is also a negative, too many modes. For the general non-technical public picking once digital mode for GMRS I think is the way to go. With the experience of multiple modes on the Hams bands I think we, Hams, can offer some recommendations that make sense and fit the GMRS service. There is a lot of equipment out there and modes in use to choose from.

Well there could be a way. People need to consider the possibility and how it could be done. I can think of one way where most of the objections are addressed. The use of digital voice might not be appropriate in some situations and advantageous in others. GMRS Digital Voice - 20221011.pdf