gman1971
-
Posts
1079 -
Joined
-
Days Won
37
Content Type
Profiles
Forums
Events
Gallery
Classifieds
Posts posted by gman1971
-
-
WRAF, I don't think I ever stated, nor implied, that anyone was/should be using the SLR8000 for GMRS. I just pointed the figures to show it on a chart. Whether it is or not part 95 accepted it is hard to argue that the figures on that thing are just amazing, plus it has additional blocking of 110 or 120 dB, so its probably loaded up with filters of all kinds... hence why that is the kind of receiver front end performance one should strive to get, compared to the bottom of the barrel GD77... which is fine for certain things.
Yes, thats it right there WRAF: "A lot of the nicer handheld radios have tracking filters on the frontend that gives them stronger desense protection, and you won't find that feature at the CCR price point."
I understand that for very advanced guys/gals, like you, the statements I've made are like 1st grade math, but for some of us who trained in other fields, this is the kind of stuff that marketing preys upon to sell CCRs. It would've saved a lot of hassles, time, and ultimately money, should I've have known about what I posted in here. Is it simplified? Yes, but so are Newton's classical mechanics vs the more complete Maxwell's equations... yet we still use Newton's for pretty much anything were v << c...
In the end its someone else's money, they can spend it however they like it. I only wrote this in an effort to help others, who may, or hopefully not, be as clueless as I was when I started buying radio gear.
G.
The SLR8000 is a terrible benchmark to use since NOBODY is using that as their primary GMRS radio, particularly as a mobile or portable (nor is it Part 95 type accepted). Repeaters are expected to have excellent desense rejection since they're usually running a 25-40 watt transmitter on the same antenna as the receiver. A lot of the nicer handheld radios have tracking filters on the frontend that gives them stronger desense protection, and you won't find that feature at the CCR price point. You get what you pay for; don't forget the cost of a new commercial radio.
-
WRAF, yes the GD77 is probably one of the worst CCRs out there. While Anytone 878 radios fare much better, these still desense easier than the EVX radios I have.
LScott, The chart was calculated using the specifications printed on the radio service manuals.
For the GD77, the selectivity figures were calculated using a VNA using a similar procedure to the one outlined here.
The sensitivity of the GD77 is claimed by the manufacturer to be -122.dBm
The point of this chart was to show at a quick glance why these radios are inferior to things like the SLR8000 repeater from Motorola... I understand desense is a fairly more complex issue, but the chart is easy to read for most people. If you can determine the noise level in you area, that is half of the battle right there.
G.
-
I just made this new thread, trying to explain the whole CCR situation from a receiver standpoint, and why those things aren't that great.
https://forums.mygmrs.com/topic/1661-the-definitive-ccr-thread-why-you-wont-really-save-anything/
G.
-
I'll start the Cheap China Radio (CCR) thread by showing this picture.
That shows the sensitivity of the receiver combined with the channel rejection filtering in dB, which means, any signal value that is above the dBm curve plot will desense the receiver. You can pretty much extrapolate this curve from the last point where it is computed if no advanced filtering is used, like the SLR8000 repeater, with over 120 dB blocking for off frequency stuff, etc.. but unless you have one of those, most mobile radios don't have that kind of additional filtering. So if you live in an are with a noise floor of -50 dBm like I do, pretty much most CCRs will fall apart and desense so bad you won't hear squat. OTOH, radios like the XPR7550e, with super tight front ends, will effortlessly reach over miles when the CCR is deaf as a rock. This also shows why more sensitivity is not better, in fact, more sensitivity with a poor front end filtering means it will desense even faster.
IMO, the graph above should be pretty much definitive as to why the pricing is directly proportional to the selectivity + sensitivity on those devices: with the Motorola SLR800 repeater leading the pack at well over 2 grand, the Vertex EVX-5300, new, was around 600 bucks, the TM-V71a, is around 350 bucks new, and well, the GD77 CCR can be purchased new for 65 dollars on eBay.
And here is a very simple procedure to gauge a CCRs performance and if its even worth the expenditure.
1) First off, If no channel selectivity figures are offered, then move on. "These are not the droids you're looking for."
2) Now get the receiver sensitivity figure, usually measured in uV, but with this nice chart you can convert it to dBm at 50 Ohm, link here: http://www.repeater-builder.com/tech-info/measuring-sensitivity/dbm2uv.pdf
3) Knowing that any signal above the receiver sensitivity threshold (at any frequency) will desense the receiver you add the selectivity in dB at 25 kHz to the receiver sensitivity in dBm, pay attention to signage, the sensitivity is negative dBm.
4) Repeat the same for 12.5 kHz. Now, some brands show even narrower kHz dB figures offered. You can add it and find out, but that is usually not as important as the real selectivity for further away signals.
5) As a general rule, any signal received within the receiver frequency range (and in the CCRs even further than that) that is stronger than the 25 kHz selectivity value calculated will desense the receiver.
Have at it, and please, correct me if I made any mistakes.
G.
-
I have a similar radio to that one, reception is lacking, and desenses fairly easily. If you can't replace the antenna then I would just get a Baofeng BF-888S for 9 dollars from Amazon.
G
-
AT the risking of possibly starting a fire, I would say that I don't consider Ham Gear mission critical either. Most of the ham stuff I've tried is flimsy, and has RF front ends that are wide as barn doors too. For example, when using my TM-V71a with a triple 5/8 over 5/8, its hammered by intermod pretty hard, mostly due to a NOAA station (and other high powered junk) blasting 2 miles from home from a 1400 foot tower..., and while the CCRs don't hear squat, the TM-V71 hears much better, but still severely desensed and the intermod hurts it really bad. I can hear the NOAA breaking on the GMRS frequencies if I don't run any filtering... In contrast, I don't have that issue with the EVX-5300 radios, even without any filtering added; sure, the EVX-5300 is only an 8 channel mobile with just a single digit numeric LED, and it won't even go below 450 Mhz, but its perfect for GMRS and also allows the option to use DMR.
Yes, exactly, a couple of CCR GD77s gave me a taste of DMR, and since then I upgraded all my GMRS FM only gear to high end DMR capable gear, but I still run it on FM. But let me tell you, once you move into high end DMR radios like the EVX-5300, you realize how bad these CCRs really are, even the Anytones (Alinco DJ-MD5) still don't hold a candle to the EVX radios from Vertex Standard (Motorola now)
We shall see how it all shakes down. Whatever the future awaits, I am ready to embrace digital the moment the regulations allow for digital voice modes on GMRS.
G.
The performance of the Btech has been quite adequate for my uses. To the repeater its about five miles through hills and trees. It is located on the flatland and designed to beam back up here into the hills. Simplex, I can cover everyone from my location within five miles using the Nagoya 701c antenna. Again, hills and trees. Its the Gold Country here in far Northern California just to give you an ideda of the terrain. And I am not using the radio for rag chewing. Others may use GMRS for different purposes and that is fine.
Would I recommend the Btech radio to a beginner in GMRS? Sure. Maybe its heresy around here, but it is a radio. I don't think I would recommend any of their mobiles. Would I also recommend moving beyond the Btech into part 90/95 equipment like Kenwood, or Icom, etc? You betcha. But just like in amateur radio, the CCRs provide an entry. (nothwithstanding all the non licensed uses, etc). Used properly, one have find great enjoyment from their Potato radio. They can talk to ISS, Satellites, as well do APRS and a whole host of other things. In fact Digital radio is being lead not from D-Star, or Fusion, but DMR and CCRs. (Think Anytone).
I went into my purchase of the Btech knowing full well what they are. But heck, the Yaesu FT-60 new I had to send back as it would not TX...so tell me again?
-
I am not saying don't buy CCR, just know what you're getting. That's all, so you don't put too much faith on those inexpensive radios.
GMRS won't do it b/c it is only FCC, but in theory, if another country who follows the FCC ruling has a GMRS repeater linked you could talk all over the world too... I know, not RF direct call, but still cool nonetheless.
And I will be picking something up for next year. It probably won't be the Midland. I do have the Kenwood F6a, TMv71a, Alinco 235, Yaesu FT 60, VX 5, VX 2, Anytone 3318E and a couple of Baofengs. Oh...forgot the old Icom 751 for HF. RF Noise is quite limited out here in the foothills of the Sierra.
Look, I know the limitations of CCRs. And I know it will fail. But for now it serves my purpose. We use GMRS for a specific purpose, which is Neighborhood Radio Fire Watch. For rag chewing, etc...I have other radios and allstar nodes. If fact, was talking to a guy from Western Australia today as I was walking up our ¼ mile driveway. Kinda nice. GMRS, CCR or not..will not do that.
73
-
-
I don't know about the Luiton, etc...
But like I stated in some other post I made, gauging your radio performance based on its ability to hit repeaters is doomed to succeed (its a useless test to gauge performance). Those BTech stuff RF performance in simplex, when there is no repeater around that is using $2000 radio gear to do the heavy lifting, in simplex, they'll simply fall flat in their face. Especially so in a congested RF area, these are just worthless pieces of junk for anything mission critical. For the money you're better off picking up a used commercial UHF portable, that will have a proper dual conversion superhet receiver with a front end that isn't wide as a barn door, nor will desense with the 89.7 latest 80s tunes radio station.
I am glad it works, but won't be surprised if it doesn't when you need it the most. It has happened to me... and since that day, no CCRs for me.
I'd take an Icom, or a Kenwood (like my TH-F6a) any day of the week over anything CCR, especially if it is for anything that is mission critical. Myself, for GMRS I own several used/new Vertex Standard EVX radios. I do use the cheapies for intercom at home, where the range I need is just 20 yards, which those afford fine, but when I walk out the door for anything that requires a radio that won't desense into oblivion? Vertex Standard all the way.
The noise at my location, measured with a VNA, is in the -50 dB threshold range in the GMRS range, I live 2 miles from a 1400 foot antenna tower, that makes nearly all the CCRs useless beyond 1/4 of a mile in simplex.
G.
Not wanting to get into the CCR battle here, but it is my understanding that Midland mobiles are re-badged Luitons. If I am wrong, please correct me. Our local area started a GMRS Neighborhood Radio Fire Watch. It has come in handy during the PG and E power shutoffs. I purchased a Btech GMRS V1 hand held with the matching Nagoya 701c antenna. It was a hurried purchase as my wife needed something for when I was to be gone for two weeks working in another city. I did not have time to aquaint her with a mobile system and how to set up for use with alternate power supply, much less getting a base antenna, etc, etc...
Maybe I have a good one, but I can reach the new repeater easily from my qth. I will invest in a different system, but at the time the Btech met our needs. My goal was to have her be able to reach at least one other person...and that it does and more so. The Btech was heard easily during nets whereas some others running the Midland products could not be heard. Part of that is of course due to antenna, location and all those variables. We live in hilly, treed terrain, so that factors in too.
All I can say is that for the money, the Btech has worked for us. I have another half a dozen various dual and triband hand helds made by the big three, as well as two different mobile/base radios, etc...so, while far from being any expert, I do know enough to get myself in trouble.
Anyway, that has been my experience. I even purchased one of those darn Btech hand helds for my neighbor across the road, He, licensed Extra, has part 90 equipment that needs ancient DOS programs to do anything...with the Btech, I was able to put in all the desired fire frequencies and air tac frequencies that he wanted and gave him the radio. It is what it is and will probably fail. But we aren't rag chewing for hours on end so it might last for a while.
As for the original question, the UV-82C is not Part 95 compliant and technically not allowed to be used for GMRS. I will leave it at that. If there is a wildfire and PG and E has the power shut off...no one will be questioning which radio I will be using to find out which road is open or closed due to fire.
Will it be Luiton or Midland? Btech GMRS, or UV 82x3, or Anytone, or an Icom 4001?
73
-
If that is the case, I am sorry.
In regards to the Godwin's law, nah, I am cool. I just like my radios too much sometimes...
G.
I think you may be unfairly characterizing the previous comment. I believe @WRAF213 was quoting the FCC’s own comments as a way of shining light on what might and might not be views and proposals the FCC would be open to entertaining. He did not claim to support or reject those views.
My own personal view is that this discussion has pretty much served its purpose and it is now time to let it go before we reach the point of Godwin’s law: https://en.m.wikipedia.org/wiki/Godwin%27s_law -
TYT radios, IMO, are some of the worst at desensing in crowded RF enviroments, so they are making it easier to look elsewhere.
The Vertex VX-5500 is a phenomal radio, can be found dirt cheap on eBay, and it has a super selective (and sensitive) receiver that will draw rings around anything TYT will make for the next two decades...
G.
-
Nope. If the FCC tried to force something like that, I'm pretty sure I wouldn't renew my license.
I still like carbureted vehicles, too. Not to mention mechanically injected diesels.
LMAO, I build electric vehicles, so I don't like either one of the above (carburetor nor fuel injection)... but who cares...
Why would the FCC force to go digital? I meant to also allow the digital stuff, honestly I don't care either way. Its not for me to decide, nor impose rules. It is just my opinion, and..., well, everyone has one.
Cheers.
G.
-
I would avoid that thing. For ~200 dollars you can find a great deal on an XPR4550 Motorola Mobile that will draw rings around that.
G.
- Radioguy7268 and kipandlee
-
2
-
Fighting against change is the surest way to failure.
One thing is to state that digital is currently not legal, and leave it at that. I understand that, its the law, and we have to respect the law. But the "resist change to the last breath" attitude, especially when defending a technology that is pretty much obsolete in terms of features and quality of transmissions, I simply don't understand your radical posture against change for the better on GMRS.
Also, the excuses and lame reasoning you've given, aside from the legality matters, which can be addressed (laws can be changed), I see no reason why digital couldn't be allowed, and offer a lot of functionality that FM analog can't offer.
You sound like the guys who fought fuel injection b/c carburetors were simpler to tune...
And if you have interference from digital systems, then perhaps you need to use more filtering and better radios... since I am using TX/RX cavities the intermod/interference problems I had are all gone.
Even if only GMRS was remain fully analog, the rest of the spectrum is ALL going digital, there will be interference no matter how hard you try to prevent the inevitable.
G.
-
LMAO... hahaha....
We now have four-letter words for people like that.
-
LMAO.. hahaha... pesky and expensive... indeed...
I would also think allowing mixed mode with FM would be great too. I believe Motorola repeaters can do both.
Oh man, I am already thinking about opening the flood gates and replace all the GMRS BF-888s house intercom with DMR... that is just going to be sooo cool... basically like those crappy old wireless phones with a station and a few extra handset, but this time on steroids!!! Dreaming is always for free tho....
hahaG.
-
Wow, considering how bad I hate RF INTERMODULATION, I really like you intermod!! haha....
Radioguy7268 is correct. FB2 would also be fine for a private system. However, the idle chit-chat that is common on GMRS is not actually permitted on the business/industrial service. But in reality, it would never be challenged anyway as nobody really cares (including the Commission).
-
Intermod, now you're talking!!! Almost like a mini GSM GMRS tower.
And now for the "dreaming is for free part" <deep breath> "....if I was made out of gold, man, I would be on TETRA faster than I can blink..." <end dream mode>
G.
Agree on the costs. But if you need spectrum in a metro area, 6.25 kHz channels that may be the only thing available. So you just eat the antenna, backup power system and additional rack space and site lease costs. Ouch.
TETRA - I forgot to mention this! As GMRS uses 25 kHz wideband channels, that could support TETRA (I think it requires 21k bandwidth, so you would have to convince the FCC to go beyond the 20K GMRS limit; its already been done in Part 90). Four TDMA slots would be more flexible than DMR's two and would further reduce message collisions among different groups. The handheld equipment is also quite nice, but still expensive.
Since we have 25 kHz channels, it may be lower cost (considering both the repeater and user equipment) to simply split a GMRS channel in half and place two DMR transmitters there.
Normal Channel Center: 462.650
New Lower Channel Center: 462.650 MHz - 0.00625 MHz = 462.64375 MHz
New Upper Channel Center: 462.650 + 0.00625 = 462.65625 MHz
I just confirmed that the Motorola SLR5700 DMR repeater can be programmed for these channel centers. Not sure about the CCRs.
This now provides four repeater timeslots or channels in the place of one wideband analog channel. Hmmm.....
Greg
-
Is this FB6 designation true? can this be verified?
Thank you.
I'll just point out that if anyone wants to do UHF DMR, the FCC already allows for that. It's called Part 90 Private Carrier (FB6 designation). Go get a 10-year license - get a Coordinated Frequency pair, and have at it. You no longer need to be concerned about getting Part 95 certified equipment, you don't need to worry about who qualifies as a "Family" member, and you can go ahead and "rent" airtime to anyone you want to, at any price you choose to. There's no requirement to charge a set amount or fee to anyone as a Private Carrier - you get to set your own rates (Zero if you wish), and you get to decide who uses your system.
In 10 years' time, DMR will probably be the defacto standard for UHF/VHF conventional systems, but the FCC is slow to recognize trends when it comes to their standards of "interoperability". I think you'll spend a bunch of time herding cats & trying to get everyone to agree on the same type of Digital modulation scheme if you try to get the FCC to make a formal rule change for Part 95 GMRS.
-
Unfortunately for the old stuff, Vocoder tech does indeed make a huge difference.... enough difference to make DMR sound better at even (arguably) half the bitrate. So it is not about the theoretical max bitrate being transmitted, its about how much those bits are actually encoding useful information, and a better compression algorithm will provide, like MP3, better audio quality at lower bitrates. I like to compare Vocoders to the Fraunhoffer MPEG Layer-3 audio (MP3) which can store audio at 1/10 the bitrate of an uncompressed PCM 16-bit WAV file and deliver near identical quality to that. Sure, an MP3 is still not as good as a 16-bit PCM uncompressed, which in theory is not as good as a true analog LP vinyl 33 RPM, but it takes 1/10th (at 128 kbps rate) the space of a PCM to send nearly identical information to the analog LP signal, and because the brain knows how to put it back together (ECC is in your brain, filling all the missing FFT analysis gaps, etc) you get a pretty much near perfect song. The MP3 codec was far superior to pretty much all of the pre-MP3 era audio codecs that preceded it. and the bitrates needed for an Mp3 to sound great were almost unheard of at the time (1:10 compression ratio in the early 90s was huge, when most consumer hard drives were still measured in megabytes) The same principle pretty much applies to newer Vocoders. Hence why I say, P25 Phase I its obsolete. Much like DMR will be made obsolete once a new Vocoder tech, or something new comes along and renders it obsolete (like Tier I DMR). GSM is obsolete not because of the more sophisticated radio modulations, but because the increased processing power than didn't exist at the sizes of today three decades ago to make such advanced modulations feasible. Newer modulations ranging from OFDM, WCDMA, LTE, QAM.... cell phones can do gigabits per second on just RF... compared to a 9600 baud FM radio the difference is measured in orders of magnitude, that is just ridiculous. So, to sum this long winded paragraph. Its about useful information density, not the bitrate, more bits doesn't mean a better useful information density. Newer Vocoders offer that, older vocoders don't.
As for Dual Capacity Diret Mode, or DCDM, it requires no infrastructure to work at all. Please understand DMR terminology (not just read it from Wikipedia) before emitting such statements, DCDM is a simplex Tier II DMR feature and pretty much any DMR Tier II compatible radio I've tried can do it. Even my 44 dollar CCR Baofeng BF-1801 DMR (a low grade GD77 clone) radios can do DCDM, and have two conversations on a simplex frequency. Can't do that with P25 Phase I, nor analog. Again, DCDM is simplex ONLY.
Then you can also go with a Tier I DMR on simplex if you want to run legacy stuff, operating the thing on full single carrier, which is obsolete too b/c you pretty much throw away all the benefits that a Tier II TDMA system has to offer.
In a Tier II DMR environment you're not limited to having to use a repeater, you can choose what kind of infrastructure use: you can go with a simplex double slot approach, simplex DCDM, or even simplex Tier I continuous single carrier. And then if you need it, you can chose the repeater double slot option too. You have infrastructure options, which you simply don't have on legacy obsolete stuff. Sure, for ham, P25 Phasie I is certainly fine, to talk about that SWR increase of the newest patch cable on the shack, that doesn't matter, but for a commercial customer, having these options, it makes the difference. (also for a family too) ETSI TS 102 361-x (DMR) was designed pretty much from the ground up to replace FM analog.
Timing slots are for the radios talking at any given moment, there is no need to create an universal timing for the entire country. At any given site, its either the radios themselves (double slot simplex, or dcdm simplex) or a repeater infrastructure that takes care of the timing, and when interconnecting different sites, either using IP Site connect, or any kind of MMDVM, b/c these convert CAI to IP, those packets get sent over the wire to be rebroadcast somewhere else, so how its timed or modulated back to CAI at destination is up to whatever is being done there. Hence why MMDVM can do all this multi mode "ham stuff", you get the IP packet, retrieve the digital voice information and pack it up as P25, NXDN, Fusion... etc.
Also, timing on a DCDM simplex setup (b/c there is no DCDM on repeaters since repeaters operate on 2 timeslots), DMR Tier II radios on DCDM simplex will select a timing leader automatically, and I can see that they will chatter once in a while for a fraction of a second to figure out the timing between all of them, so when you press the PTT, all the radios are already synced up and communication happens.
In regard to DMR radio mixed mode, my Alinco DJ-MD5 does DCDM simplex with mixed mode analog+digital on the same channel, and will transmit back on whatever modulation the last received transmission was on just fine: It can listen and demodulate correctly DMR or analog depending on the signal that is being received. There is no "interoperability" with FM problem there, but at the same time I have all the DMR Tier II options that a legacy system like P25 Phase I simply lacks.
I still don't understand why range, or operating near threshold is relevant to this discussion? Nobody has argued that having better audio to threshold is bad. DMR has that too.... but FM wideband will still reach further. In addition, RF range can be extended using the right infrastructure, better radios, or both.
As for hearing kids on GMRS: here is what happens. First off, I don't hear them breaking the squelch, ever, I never said that. when I hear them is when key my BF-888S running @ 1 watt power, which opens the squelch on all the radios used in the intercom, but if at the same time I am keying my intercom, a 5W portable starts talking, I can hear both radios on the channel. That is the issue I've experienced, which has nothing to do with signaling. Now, when testing DMR all we noticed was a slightly lower audio quality.
G.
DCDM is part of the standard, but standardization isn't the problem. DCDM requires infrastructure, specifically a timing master, in order to keep units synchronized. Handhelds are capable of being the timing master, but their range is poor and the necessary beaconing will drain the batteries. DCDM does not work on mixed systems because there is no way to guarantee there's just one station claiming timing master. In effect, timeslots can't be established on the nationwide, uncoordinated channels that GMRS has. The signaling a repeater uses to establish timeslots is embedded between each timeslot. TDMA transmitters (either on the repeater's input or in simplex mode) don't transmit during that period, since that's a guard period between transmissions.
In TDMA direct mode, an elected channel timing leader MS shall establish the timing reference for both time slots on the frequency. MS units that are not the channel timing leader are responsible for retransmitting the timing reference out to the edge of the wide area system. This mechanism helps to ensure that all MS units in the wide area system are working from the same timing reference. In general a MS transmits in the appropriate slot with the channel slot timing established by the channel timing leader MS.
I was making specific reference to the post-2017 laws. What you're saying in that last post isn't consistent with what you said in your first post (P25 is obsolete vs. P25 offers nothing analog+DTMF can). P25 Phase 1 is still the ONLY P25 format for conventional operation, and it will be some time before we see any format include true direct-mode timeslotting. The hidden-node problem would prevent a radio from using whatever voice traffic it hears out there as a timing master. Solving that would require GPS timeslot edge references (not unattainable with current technology), which would increase equipment costs up to the public-safety realm. I don't think very many of us bought our radios new from a dealer, so we wouldn't be the market for it. Equipment cost is a real concern when the issue of FRS interoperability is introduced; it's still a band for toy radios for your kids.
P25 runs the vocoder at a higher rate than DMR, and equivalently has a higher data rate (7200bps vs. 3600bps after ECC). Yes, the vocoder is inferior, but it still fits in more voice information. Of course wideband FM is better, but that isn't what the topic is about. All digital voice modes will exceed narrowband FM at decode threshold, that's one of the biggest advantages of using digital voice and isn't an advantage of any one format. DMR uses less power for the same signal but only half of the channel's bandwidth can be realized.
This whole thread is just an example of why we'll be using analog for the next twenty years.
-
Holy pendantic bold caps reply man. Would you please read carefully what I said before jumping the gun? On my earlier post I stated very clearly that A) I don't care if people hear my stuff (as in, I have no expectation for privacy). B ) I also stated NOT use encryption, b/c, once again, its illegal. But thanks for reiterating what I've stated already in an all bold caps statement.
Oh, and I have a cellphone if I want privacy. (more like 10 of them, but whatever)
The GMRS regulations in effect are the ones post-2017, I use whatever regulations are currently in effect, b/c you know, that is what the FCC laws currently say. If you want to use old laws that have been superseded, that is your call, not mine.
Who said P25 was encryption?... not me, so, where did you get that from? I am fully aware that P25 is just another digital format based on the AMBE2 vocoder, etc.
Now, here is what I did said, and I will repeat it: P25 phase I is obsolete. And FM does offer DTMF signaling, sure, its not embedded, but you can achieve the SAME type of signaling for opening different radios, etc, on analog FM. I've done it in the past, is not as clean as DMR, but it can be done.
What? ham MMDVM is not equally compatible, dude, Multi Mode Digital Voice Modems are just devices that "translate" CAI to IP packets, not a ham digital format.
And why are we bringing here the fact it operates better at threshold? why is that relevant? It is pretty much a fact that FM wideband can reach further than anything digital at the moment. Sure, its arguably not going to be crystal clear, but you can copy stuff that the best digital radios simply won't decode... and then, there is always the cellphone.
As for P25 better quality than DMR, yeah, that is like your opinion, man, and everyone has one. That's not factual, b/c now here is my opinion, I think P25 sounds worse than Motorola XPR or Vertex EVX high end DMR radios. So, who is right? who cares.
Now, here are the facts, on DMR you CAN have:
-Single Frequency repeaters.
-Single Frequency, two concurrent conversations.
I think there is some confusion here: There is Tier I DMR which is basically no timeslots, no pulsing, and effectively a single 12.5 kHz digital carrier, the same as P25 Phase I. And then there is Tier II Dual Capacity Direct Mode, which allows for two concurrent calls on a simplex channel, and that is AFAIK, part of the DMR ETSI standard. Then there is Tier II Repeater Operation, which uses two timeslots on receive and two timeslots on transmit. So on any given repeater you can have 2 concurrent conversations using a repeater pair of frequencies, and I believe that with the advanced Moto repeaters you can do pseudo trunking using the timeslots so you can have more than just 2 voice channels.
When you say that one timeslot is wasted, Its not wasted, the other timeslot is just available for a 2nd conversation to take place. But hey, wait a minute... you can't have two conversations on the same channel on P25 Phase I.
G.
PRIVACY DOES NOT BELONG IN GMRS! That's EXACTLY why we're using analog! See 95.1733(c ):
(3) Coded messages or messages with hidden meanings (“10 codes” are permissible);
Everyone is supposed to be able to hear everyone, and there is no expectation of privacy; in fact, there should be a reasonable expectation that others are able to hear you. RAS obfuscates transmissions even though it is not voice encryption. If you don't want to hear kids on pink Barbie radios or you don't want them to hear you, then you shouldn't be using post-2017 GMRS.
What? P25 is not encryption, it's a digital voice format the same way DMR/NXDN is, and ham stuff like MMDVM is equally compatible. Digital voice operates better at FM threshold and/or with mobile flutter. P25, like other digital voice formats, also has embedded signaling, which analog FM can't offer.
DMR is 6.25 kHz-equivalent narrowband on repeaters only (yes, there's DCDM, but that's proprietary), and has worse voice quality than P25. The other timeslot gets wasted in direct mode with Tier I or II operation. dPMR and NXDN48 do not have that limitation due to their 6.25 kHz bandwidth, while P25 and NXDN96 put more data in a 12.5 kHz bandwidth.
-
Wow WRAF213, amazing info, thank you!
-
Well, my understanding is that GMRS was devised for family use, so why would anyone who is licensed want an unlicensed person, with an easy to acquire bubble pack radio, hear all their family traffic and cause interference, be it intentional or non-intentional. Now, I am fully aware that I can't prevent my radio signals from being listened by others (nor I have a need to prevent that), but say, if I switched tomorrow my entire GMRS setup to digital DMR, added RAS to a short range intercom repeater to limit who can talk through the repeater (not even going with AES encryption), etc, then all the neighbor kids who bought these 5W FRS radios after seeing the "cool" antennas going up on the roof of my house, these kids will no longer hear us talking on my house intercom, nor we'll hear them yap when we talk through the intercom and they also happen to be talking on their 5W portable as well.
Ham radio, amongst other reasons it was meant for tinkering and EMCOM, and you need a license to use it. The problem is, you see, that most 5 year olds can't get a ticket, most significant others (male and female alike) might not be interested enough to bother taking the exam, etc, so now, if you have a large family, say, 4 or 5 kids and wife, even if it was a family of little Mozarts who all were able to get their tech license by age of 4, the moment those 4-5 year old kids start swamping the ham channels with kid's talk about their latest GiJoe toy, or the Barbie that is pink, etc, the typical grumpo self-righteous ham operator will railroad the channel and assert grumpo dominance by stating "hey kids, you've hogged this frequency for your personal stuff, you need to move elsewhere.... this channel might be needed in an emergency situation." Even if all the 4 year olds were ham licensed. The moment anyone railroads on a private radio conversation for no reason, even if its a bunch of 4 years old, unless its an emergency, that anyone is the one causing harmful interference to those licensed operators, who where talking Barbies or pink unicorns on a ham frequency.
While the regulations are what they are now, it doesn't mean we can consider and discuss a future. Life is not set in stone, things evolve.
May I ask why P25 Phase I over analog FM? So they can run encryption? Which, BTW, its illegal to encrypt stuff in GMRS. P25 Phase I is the same thing as FM, it has nothing that can't be offered in FM analog with a DTMF setup.
Now, once you enter TDMA territory, the fact that you can have two conversations on a single frequency, and single frequency REAL TIME repeaters, which will make any radio a hotspot, etc, then P25 Phase I is, simply put, obsolete, b/c it doesn't offer anything that FM can't offer already, and then, like DMR, its not interoperable with FM either. So, IMO, if you are going to get digital, there has to be a reason, beyond having the little encryption checkbox, to make the swap. That reason, for me, the reason why I would go digital DMR is b/c I could implement single frequency repeaters (as in , receive in TimeSlot 1 and immediatly retransmit on TimeSlot 2, single frequency, no delays, NOT a simplex repeater) and then have two conversations going on at the same time on a single frequency, all that without having to buy any additional infrastructure. Can't touch that with FM nor P25 Phase I.
G.
My biggest issue with digital on GMRS is the lack of interoperability. Different modes don't talk to different modes, and analog users (which would be all FRS users and all existing type-accepted GMRS equipment) will have no hope of ever being able to understand what is being said on a digital system. The only people who'd immediately benefit from a rule change are those who aren't using Part 95 equipment. Most importantly, 95.1731(a), (
(1), and (c ) would no longer be effective if stations were no longer able to communicate due to differing modulations.The FCC has already explained why they aren't going to do digital voice on GMRS, and they cite this reasoning:
CTCSS/DCS is a flimsy excuse since operators using tone squelch can easily disable it to monitor for other traffic, and users with priority traffic can transmit with tone squelch. Even if they have to do it on a split-tone repeater's output frequency, there's still the chance that they'll be heard. Commercial digital radios are designed to mute traffic sent to other destinations (for example, private calls on DMR), so traffic addressing becomes a factor and impedes the capabilities of listen-before-talk. Promiscuous mode is not a standard feature.
Dual certification is more difficult after 6.25-equivalent narrowbanding requirements began to get implemented in Part 90, since the radio would be capable of transmitting a non-compliant emission designator or scrambled/encrypted traffic on GMRS channels. A set of significant changes to the programming software could resolve the issue, but that's additional costs and confusion for us and less planned obsolescence for the radio manufacturers. It's not impossible for a 6.25e radio to get dual certification since there's no requirement to prevent users from programming digital channels onto GMRS channels, but it's a big can of worms for the FCC and extra costs for the manufacturer.
If I had to pick a mode, and if licensing/equipment costs were assumed to be negligible, I would endorse P25 Phase 1. It's theoretically vendor-neutral, easy to modulate, better suited on simplex operation (NAC of F7E and non-talkgroup operation), and most of the equipment already out there already has mixed-mode capability. Unfortunately, we can't trust everyone to properly program their radios for mixed-mode operation and listen-before-talk.
GMRS isn't the place to set up commercial-type repeater systems, it's a place for travelers and family members to talk to each other. That's why we have the amateur bands.
-
The NXDN 6.25 is, IMO, nothing but a gimmick. For the non-tech person it looks like a panacea. And at first glance, its pretty obvious that you want to do FDMA and not TDMA, but once you start calculating budgets and figuring out what you need, you quickly realize that double the equipment per frequency is in order, with even tighter filtering, so twice or triple the cost of a TDMA solution.
IMO, again, IMO, for a less complex 2-way radio system (vs a cellphone system), I think a TDMA solution makes a much better use of the spectrum (like GSM did). And, again, personally, if I could afford to run TETRA I really would, I really like the TETRA b/c it has 4 timeslots vs just 2 slot of DMR. A TETRA implementation on GMRS would actually make the use of repeaters great, b/c now 4 guys can be talking simultaneously without messing with each other's talks. You can now use a public repeater to selectively call IDs (groups, individuals), rather than keying the repeater (and all that are linked to it) at 3:25 AM in the morning and waking everyone up to hear "WXZX1245, hey honey, I am going home." And lets not forget that, effectively, with a DMR/TETRA GMRS solution in place, most folks would have little need to build their own repeater for a less public (not encrypted) channel. Making good repeaters (like the Madison 700) now a viable option to have a group call with just your family so it doesn't open the squelch for a guy sitting in Indiana, who probably isn't very interested in hearing when you're going home. Maybe he is, but if so, he can run a nice thing called "promiscuous mode" so you can hear all traffic in the linked repeater network, but then, that is HIS choice. For a public GMRS DMR I would also filter ANY and ALL encrypted calls. Don't run encrypted crap, please, thank you.
One possible way to do this on DMR would be: Assuming a hierarchy of Repeater -> Call Sign -> Family. Lets begin by assigning a repeater Group Call ID for every repeater, this Repeater Group Call ID will be issued to all the radios that connect to it via direct RF, so for example, for the Madison 700, the Group Call ID could be, say, ID 1000, and consequently all the registered radios that are in the Madison area will be listening to the 1000 Group Call. Then, when a new licensee signs up on the repeater, they get assigned two DMR IDs, first one is a Group Call ID, linked to your callsign, which will be then subsequently used by anyone under your callsign (ie. family) and a Private ID just for any new radio you get. So, now, when the wife gets a radio, all you get is another private DMR ID for that radio, and set the radio to listen to both the Group Call ID under your callsign and the Group Call for the repeater. So, now that GMRS repeater has become a pretty viable family comm service (which is what GMRS was meant to be) And then, b/c DMR allows to have 2 people talking at the same time (even more I think with the higher end Moto stuff) so again, digital makes so much more sense IMO. So you can effectively utilize repeaters like the Madison 700 area to do what GMRS was really meant for, and without bugging everyone and their mother (and especially when the repeater is linked all the way to Indiana from Wisconsin... holy cow, my simple radio call "WQXXXX, hey honey, I am going home" was heard all the way down to Indiana... that doesn't sound very appealing to a lot of people, hence there will be much less "repeater proliferation")
That is just for basic GMRS family comms. But then you can create Group Calls for different things, like hobbies, say, there is a buch of GMRS guys who like RC planes and another who really likes "basket weaving", or guns, or Corvettes? No problem, create several group calls, ID 40001, 40002... so on so forth, and if you like RC planes, you just add that group ID to your personal radio, or if you like basket weaving you listen to that ID, so the guys who hate "basket weaving" don't have to listen to the "basket weavers" yap all day long about how awesome it is,etc. Same goes for RC planes, or whatever it is that floats your boat.
Again, this is just my opinion, I clearly understand that the current FCC regulations don't allow for any digital modulation at the time of this writing, so don't use digital, but then again, dreaming is for free.
G.
Why "More Power" Isn't The Answer
in Technical Discussion
Posted
Absolutely! One can never be too careful