Digital voice on GMRS

[jonwienke]

TDMA causes trash, due to the continuous re-keying of the transmitter. Every time a transmitter keys, it takes a split second to stabilize, thus producing crap that splashes all over the place.

If that was true, the FCC would never have approved TDMA, and there wouldn't be any such thing as DMR or P25 phase 2.

 

[12dbsinad]

There are zero square waves in any digitally modulated RF signal. It never happens, or it would be impossible to fit digital RF into any reasonable channel width, and you'd have strong odd harmonics that would destroy the digital signal if you tried to filter them out.

For someone claiming superior knowledge, you're remarkably ignorant of some of the basic fundamentals of radio.

That's simply not true. They may not be perfect square waves but they are considered such. Do yourself a favor and look it up. Search "digital vs analog waveform"

You have no idea what you're talking about.

 

[russbrill]

There is no standard for Part 90 use and you will find just about every format there. You can find analog, or DMR or NXDN all used on the same frequency.

My post was referring to Part-97 and Part-95 users...

 

[12dbsinad]

If that was true, the FCC would never have approved TDMA, and there wouldn't be any such thing as DMR or P25 phase 2.

Of course it's true. Did you not hear of all the issues DMR has produced, VHF more specifically? Did you know what the FCC reactions were? This is because DMR or TDMA is dirty. You don't have to believe it, you're free to believe whatever crazy thing you want to believe.

Again, a little searching will go a long way. It's funny you have the audacity to call me ignorant of radio. That's hilarious.

It's funny that you think the buck stops at the FCC in regards to interference. Look at all the problems on T Band now with the shuffling of DTV. But, I will agree that they did do the right thing in regards to GMRS. They don't want problems, and there is no money in it.

 

[russbrill]

If that was true, the FCC would never have approved TDMA, and there wouldn't be any such thing as DMR or P25 phase 2.

Hmmm, I don't know about that.. The Commissioner hacks at the FCC are mostly Politicians looking to get paid..

 

[jonwienke]

That's simply not true. They may not be perfect square waves but they are considered such. Do yourself a favor and look it up. Search "digital vs analog waveform"

You have no idea what you're talking about.

Actually, I do. The data bits being modulated go to the modulator as mostly-square waves, but the digitally modulated RF signal does not contain any square waves whatsoever. Do yourself a favor and look it up.

Of course it's true. Did you not hear of all the issues DMR has produced, VHF more specifically? Did you know what the FCC reactions were? This is because DMR or TDMA is dirty. You don't have to believe it, you're free to believe whatever crazy thing you want to believe.

P25 Phase 2 is also TDMA. Are you claiming it's inherently "dirty", too?

Cite your source for your claim that all DMR signals splatter. I have no issue believing that there are individual poorly aligned or configured DMR transmitters out in the wild that splatter more out-of-channel signal than allowed by the factory specs, but I'm calling BS on your claim that that's true of every FCC type accepted DMR transmitter ever manufactured.

Again, a little searching will go a long way. It's funny you have the audacity to call me ignorant of radio. That's hilarious.

When you keep saying stuff that's easily disproven, yeah, I'm going to say it, and keep saying it.

 

[12dbsinad]

P25 Phase 2 is also TDMA. Are you claiming it's inherently "dirty", too?

Cite your source for your claim that all DMR signals splatter. I have no issue believing that there are individual poorly aligned or configured DMR transmitters out in the wild that splatter more out-of-channel signal than allowed by the factory specs, but I'm calling BS on your claim that that's true of every FCC type accepted DMR transmitter ever manufactured.

It all depends on the manufacturer. The FCC spec is 60db, some equipment barely meet this. The good ones exceed FCC specs at around 80-90db.
"Dirty" is the inherent nature of pulsing a transmitter. For example, take SCADA radio's that operate on the part 90 band. Those meet FCC spec, yet they are the dirties things you've ever seen because they produce trash and are very cheaply built.

What exactly do you think GMRS guys are going to do if digital is allowed? Buy the cheapest Baofeng repeater for 75 bucks and throw it on the air, combined with CCR non certified DMR radio's.

I think you'd find that if the FCC allows digital on GMRS, they will get rid of the repeaters, just like what was talked about at the last review and make it one big simplex digital glorified CB.

Furthermore, it wouldn't be just a simple "yep, you can use digital". You wouldn't have many choices on DMR repeaters as most aren't certified for GMRS use anyway, as well as the radio's. So what does that mean? Make a rule change to get rid of part 95, or allow the Baofengs and TYT's of the world to start trying to certify their DMR garbage for GMRS? And what about existing analog wideband repeaters?
narrowbanding probably need to happen at that point. All of which the FCC probably has no intentions on doing. All they care about is auctioning frequencies and making billions of dollars.

 

[bill4long]

That's simply not true. They may not be perfect square waves but they are considered such. Do yourself a favor and look it up. Search "digital vs analog waveform"

Um, all the digital voice modes use 4-state FSK to transmit the data using four sine-wave subfrequencies, modulated as FM on the carrier. The 4 states logically map to 4 digital values of 0, 1, 2, 3, representing 2 digital bits, i.e, 00, 01, 10, and 11, binary. But the four frequencies are modulated on the carrier as sine waves.

You can read about it here:

StackPath

 

[NC1]

QUOTE: What exactly do you think GMRS guys are going to do if digital is allowed? Buy the cheapest Baofeng repeater for 75 bucks and throw it on the air, combined with CCR non certified DMR radio's.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
THAT, right there is precisely what WILL happen. But why would the repeater owner care?
It was made very clear in post #134 by prcguy: " To be frank, some of us don't care about other license holders and we want digital."

So in other words, if you don't like digital, then go away and find something you like, because once it's digital it's our playground to crap all over.
To which my attitude is: if you don't like analog, then go away and find something you like, because it's here now to stay for the foreseeable future.

 

[12dbsinad]

Um, all the digital voice modes use 4-state FSK to transmit the data using four sine-wave subfrequencies, modulated as FM on the carrier. The 4 states logically map to 4 digital values of 0, 1, 2, 3, representing 2 digital bits, i.e, 00, 01, 10, and 11, binary. But the four frequencies are modulated on the carrier as sine waves.

You can read about it here:

StackPath

Yep, you're right. I misspoke, I forget that FSK is not "true digital". I'll blame it on getting old...

Jonwienke gets a cookie..

 

[bill4long]

Yep, you're right. I misspoke, I forget that FSK is not "true digital". I'll blame it on getting old...

Of course it's true digital. A discrete (finite) set of four states. That's what digital means.

 

[12dbsinad]

Of course it's true digital. A discrete (finite) set of four states. That's what digital means.

I was being facetious.

 

[jonwienke]

It all depends on the manufacturer. The FCC spec is 60db, some equipment barely meet this. The good ones exceed FCC specs at around 80-90db.
"Dirty" is the inherent nature of pulsing a transmitter.

This is illogical schizophrenia at its finest. If a DMR transmitter meets or exceeds the 60dB FCC specification for spurious emissions, then it's not "dirty", or at least no more so than any analog transmitter that also meets the specification. A transmitter has to have spurious emissions to be "dirty". Congratuilations, you've just disproved your own argument.

Or are you claiming that no DMR transmittter meets the 60dB specification? And if so, on what basis?

 

[RFI-EMI-GUY]

Actually, I do. The data bits being modulated go to the modulator as mostly-square waves, but the digitally modulated RF signal does not contain any square waves whatsoever. Do yourself a favor and look it up.


P25 Phase 2 is also TDMA. Are you claiming it's inherently "dirty", too?

Cite your source for your claim that all DMR signals splatter. I have no issue believing that there are individual poorly aligned or configured DMR transmitters out in the wild that splatter more out-of-channel signal than allowed by the factory specs, but I'm calling BS on your claim that that's true of every FCC type accepted DMR transmitter ever manufactured.


When you keep saying stuff that's easily disproven, yeah, I'm going to say it, and keep saying it.

It really depends upon the domain. the data feeding the modulator is indeed square wave. DMR uses 4FSK modulator which is a scheme where the data fed in is parsed into di-bits (symbols) representing one of four states of deviation . This occurs at the data rate of 4800 bps.

Instantaneously only one state of deviation can occur in the time domain, so at the moment of one state, a precise single tone is transmitted at a deviation about the center frequency per below. There is a filter to contain the modulation mask within the channel as prescribed by the regulatory agency.

A big difference between the digital waveform and analog is the modulation density. The digital modulation utilizes 100% of the available bandwidth while analog has far lower occupancy and therefore, energy available to interfere with co or adjacent channels.

01	carrier-deviation
00	carrier-(1/3)*deviation
10	carrier+(1/3)*deviation
11	carrier+deviation

2FSK vs 4FSK | Difference between 2FSK and 4FSK modulation

This page compares 2FSK modulation vs 4FSK modulation and mentions difference between 2FSK modulation and 4FSK modulation types.2FSK Modulator and 4FSK modulator are used for these modulation types.The links to difference between various modulation types such as QAM,BPSK,QPSK,OQPSK are also...

www.rfwireless-world.com

"Modulation measurements serve to check the signal quality, which should fulfil the requirements in order to achieve coverage and immunity to interference. At an interval of 1/4,800 seconds, DMR-specific 4FSK modulation generates frequency deviations of theoretically ±0.648 or ±1.944KHz, depending on the symbol transmitted; a symbol, in turn, contains two bits of information. The modulation is regarded at the defined symbol times. "

Professional radio with DMR test and technology

Achim Grolman of test and measurement product manufacturer Aeroflex explains why more medium-sized operations are relying on the DMR standard and looks at how DMR devices are tested

www.itproportal.com

 

[12dbsinad]

This is illogical schizophrenia at its finest. If a DMR transmitter meets or exceeds the 60dB FCC specification for spurious emissions, then it's not "dirty", or at least no more so than any analog transmitter that also meets the specification. A transmitter has to have spurious emissions to be "dirty". Congratuilations, you've just disproved your own argument.

Or are you claiming that no DMR transmittter meets the 60dB specification? And if so, on what basis?

I don’t know, you tell me. I gave you an example of SCADA radio’s, and those are part 90 approved. I’m just telling you what I see out in the real world. I mean after all, they are approving Baofengs for GMRS now aren't they?

 

[jonwienke]

View attachment 100941

My point is that FM capture occurs on the highest amplitude RF signal peak within the channel. When the RF energy is fairly evenly distributed throughout the channel, more total RF energy is required to present the highest amplitude RF signal peak than if it is concentrated on a single frequency in the form of an unmodulated carrier.

Therefore, an unmodulated carrier is the most effective form of co-channel interference, but is less likely to cause adjacent channel interference.

 

[12dbsinad]

My point is that FM capture occurs on the highest amplitude RF signal peak within the channel. When the RF energy is fairly evenly distributed throughout the channel, more total RF energy is required to present the highest amplitude RF signal peak than if it is concentrated on a single frequency in the form of an unmodulated carrier.

Therefore, an unmodulated carrier is the most effective form of co-channel interference, but is less likely to cause adjacent channel interference.

Digital because it's at full modulation. If 2 signals of the same power are heard, one non modulated and the other DMR, you will for sure hear the digital hash before the quite unmodulated signal.

 

[jonwienke]

I don’t know, you tell me. I gave you an example of SCADA radio’s, and those are part 90 approved.

Which are mostly 900MHz spread spectrum, not DMR/TDMA...

Non sequitur.

 

[12dbsinad]

Which are mostly 900MHz spread spectrum, not DMR/TDMA...

Non sequitur.

Not around me, mostly 450-470 band and have caused all kinds of problems

 

[jonwienke]

Digital because it's at full modulation. If 2 signals of the same power are heard, one non modulated and the other DMR, you will for sure hear the digital hash before the quite unmodulated signal.

On AM, yes. On FM, not so much.