Analog coverage vs IMBE Astro coverage

[nmfire10]

Part one: What have you found from ACTUAL REAL-WORD experience. Not what a salesman claims.
What will produce more useful audio at the outer reaches of system coverage: IMBE or Analog. I understand there is error correction with IMBE that could theoretically help make up for a noisy far away analog signal. But I also can't help but think that can only go so far and eventually, its just going to give up and listening closely to an analog signal would work better.

Now riddle me this. Lets say you have a school where there is no radio reception inside the building. Lets say that someone claims that by modulating in IMBE, you magically have instant radio coverage inside the building. This to me sounds like total BS but I have not actually gone in there to try. What say you?

[CTAMontrose]

We had a VHF Quantar on the hammy band with a user on it that was camping at a state park, his radio was an XTS3000 with current firmware, and all radios had AGC enabled with motorolas recommended settings.

That said, in astro he would at times sound robotic and tinny, and occasionally drop packets, but we were able to communicate and his messages got thru. When he switched to analog, there was so much noise on his signal we could not copy the voice contained in the signal.

In a properly designed and programmed astro system, you can have communications at a little beyond the analog coverage, this has been demonstrated in the lab as well using service monitors etc. Now if you have a crappy system, old firmware and not programmed properly then analog can outperform digital.

[Wicho]

Yeah, uh...I'm gonna let escomm answer this one.

[6V6GT]

We haven't seen any loss of coverage going from analog to P25. We went from an MSF 5000 to a Quantar on our test site and all is well. Our attempts at going over to analog when the digital becomes unusable have had similar results.


Tim

[Elroy Jetson]

My own experiments would agree with those you just read.

But, it does take some time to adjust to the different sound of IMBE digital voices. It's a bit odd. Certainly IMBE doesn't sound as clear or as good as
analog voice at or near full quieting. But its coverage range is at least equal to analog IF everything is set up properly.


Elroy

[6V6GT]

True- to a point. Using Astro Spectras the analog audio is quite thin and never sounds great. Other analog radios sound far better. However when the are in P25 mode the audio becomes much fuller and has better "fidelity". With an EFJ 5100 the audio sounds pretty good either way. With an XTS 3000 the analog is not quite as good but the digital is okay. There are a lot of variables at work here and a shortage of P25 radios to compare. Overall I like the P25 better- the digital artifacts are easier to overlook than noisy analog.

[Wowbagger]

I think the biggest issue with going from analog to digital - be it NBFM to APCO-25, or AMPS to CDMA, or whatever - is that with analog, the operator gets feedback as to the signal strength in the form of static. So as the operator gets further from the transmitter, he starts to hear static, and quickly learns when things are going to go bye-bye and takes that into account.

With digital, you are fine until you aren't - then you are dead. Once the signal level drops enough that the BER is greater than the error correction's ability to fix it, then it isn't very far until you are at 50%BER - bye-bye.

I almost think they ought to have the radios monitor the RSSI and inject a bit of static inversely proportional, to signal to the user what's going on.

[MTS2000des]

I think the biggest issue with going from analog to digital - be it NBFM to APCO-25, or AMPS to CDMA, or whatever - is that with analog, the operator gets feedback as to the signal strength in the form of static. So as the operator gets further from the transmitter, he starts to hear static, and quickly learns when things are going to go bye-bye and takes that into account.

With digital, you are fine until you aren't - then you are dead. Once the signal level drops enough that the BER is greater than the error correction's ability to fix it, then it isn't very far until you are at 50%BER - bye-bye.

I almost think they ought to have the radios monitor the RSSI and inject a bit of static inversely proportional, to signal to the user what's going on.

and to further expound on this excellent point is that the operator is totally reliant upon the DSP/CPU/CODEC to provide 100 percent of the perceptual coding. What I mean by this is as a dispatcher, you eventually get used to hearing nuances, even subtle ones, of transmissions of particular users over time. You can tell that an officer is "code 4" just by the sound of him keying his mike a certain way, the background audio, the noise level, etc. You get good at being able to decipher what someone is saying into the noise floor. As a ham we do this all the time on HF. Dispatchers do it as well everyday on FM systems.

It becomes second nature. When you move into the digital domain, it is a world of absolutes. You either have signal, and thus intelligence, or nothing at all. So I guess the point is that a digital system HAS to be instituted correctly and no corners cut like is often done in analog systems for the users and dispatchers are 100 percent reliant on the codecs, DSP and CPU's to work.

[Pj]

On a side note... anyone play with the "coverage imbalance indicator" options? IIRC, this should work for conventional as well as trunked. Any details? I have it enabled in my radio for the simplex channels we use, but I don't notice anything on the display or alert tones (yes, recent firmware for all)

[escomm]

In a properly designed and programmed astro system, you can have communications at a little beyond the analog coverage, this has been demonstrated in the lab as well using service monitors etc. Now if you have a crappy system, old firmware and not programmed properly then analog can outperform digital.

Without getting into the astro vs analog debate, I will only say that I do not believe these claims about lab testing finding that astro coverage is actually "further out" than analog are accurate. There is a curve, often used by Motorola (and I'm sure every other purveyor of P25 equipment--my gut is that it comes from DVSI) that indicates that analog has better "performance" at the very top of the signal strength->performance curve and the very bottom of the signal strength->performance curve.

And as for Astro providing better coverage, I can only refer to my comparison of the LAPD and LAFD radio systems. LAPD uses astro on UHF, LAFD uses analog on 800. LAPD's radio system has 23 transmitters, and coverage is usually rated at about 95% of the city. LAFD's radio system has 9 transmitters (all colocated at sites used by the LAPD) and last I recall they claimed 98% coverage. LAPD's MDT system runs on 800 and they are forced to dispatch calls in dead spots via the MDT because the radios do not work.

Please let me qualify the preceding paragraphs by noting that the situation here in LA has dynamics not necessarily seen elsewhere (for instance, LAPD's radios do not have anywhere near current host/DSP, the philosophy on maintenance is more "reactive" than "proactive", the radios are all very old and in poor shape), and there are so many variables that affect overall system performance that discussing them would result in an encyclopedia if not an entire library. I only bring it up as a rough ballpark comparison of two systems designed with the same goals in mind (coverage range, reliability, critical mission and so on) and the vast difference in what it took to accomplish those goals.

That all said, I will concede that a properly designed, built, and maintained astro system will perform extremely well, and if any one of those three components are removed from the equation then overall performance suffers greatly. Astro radios with good signal strength and current host/DSP and programming setup sound absolutely pristine. There is no doubt about this, and the audio quality that comes out truly comes close to a fully-quieted analog signal (but does NOT match it or exceed it )

I will also point out that rolling out an astro system will cost 5 to 10 times more than a conventional system, and the maintenance and personnel training costs are a few orders of magnitude higher than that of analog. And with all the jazzy IP-based stuff coming out, it's only going to get worse.

[Elroy Jetson]

I agree. Radio technicians will have to become more and more like network IT techs as time goes on. We'll have to handle more than just
the physical radio and how it operates, but all that IP stuff will become part of our jobs, too.

I prefer to avoid computer networking issues. Pain in the backside. Now I guess I'll be getting into it ANYWAY if I continue to work
as a radio tech. Eventually.

As for voice quality, while P25 sounds a bit odd through an Astro Saber, you should hear it through a M/A-Com P7100IP. It's FAR
inferior in voice quality. It sounds like Stephen Hawking's voice synthesizer with a bad cold!

But maybe my radio doesn't have the most up-to-date revisions in it. Be that as it may, my Astro Sabers kick the 7100's butt, and they're
ten years older.

Elroy

[Rayjk110]

Try enabling DVRS (If you're using an Astro25 portable). If you're making the repeater (I tested using a 5k and a Quantar on UHF), you get the 3 quick beeps [think trunking RTT tone]. If you're not making it, you get the set of low beeps [failsoft PTT tone]. Now, I'm not sure what DVRS is for or what the intent is, but it works fine for me as sort of a signal indicator.

[motorola_otaku]

I can throw in a couple of cents on interference issues.

If you have co-channel users on analog, and they are close enough that you can hear them on your subscriber equipment on a routine basis, you are going to have problems. Let's say you're in an area where coverage is about average on your system, and your co-channel user transmits in analog. Whereas you'd get the "wavering" sound in analog but still be able to hear your party, in digital you get packet loss that can range from moderate to complete. Obviously there are a whole slew of variables that come into play here, but it's still something to consider.

This problem also rears its head on adjacent frequencies, particularly when the analog signal and the IMBE signal are less than 25kHz apart and the analog user is using 25kHz equipment. Friendswood (TX) VFD and the Texas DPS (highway patrol) learned this the hard way. In their case the interference was from digital to the analog equipment, but it's not inconceivable that the problem could go both ways.

[Rayjk110]

Yeah I've found that even the slightest analog signal on a digital freq. will result in at least some packet loss.

[wavetar]

I agree. Radio technicians will have to become more and more like network IT techs as time goes on. We'll have to handle more than just
the physical radio and how it operates, but all that IP stuff will become part of our jobs, too.

If you work in a shop of any size, you have to become much more computer savvy for many other apsects of your job as well, be it Canopy/Mesh type solutions and even working with Bluetree or other modems on AVL systems...especially if they're 'in house' software packages. MotoTRBO requires even more in-depth I.T. knowledge for it's text messaging & AVL.

I prefer to avoid computer networking issues. Pain in the backside.

You & me both...you get dragged into becoming their network support person for anything that happens to affect what you've installed, even though the problem could originate elsewhere in the system.

[PhillyPhoto]

And as for Astro providing better coverage, I can only refer to my comparison of the LAPD and LAFD radio systems. LAPD uses astro on UHF, LAFD uses analog on 800. LAPD's radio system has 23 transmitters, and coverage is usually rated at about 95% of the city. LAFD's radio system has 9 transmitters (all colocated at sites used by the LAPD) and last I recall they claimed 98% coverage. LAPD's MDT system runs on 800 and they are forced to dispatch calls in dead spots via the MDT because the radios do not work.

Do you know what type of radios are being used? If the FD is using 30 watt mobiles, and the PD is using 5 watt portables, I would expect the difference in capabilities. LAPD needs to step up to at least current technology, and drop the old radios. Just my 2 cents...

[Elroy Jetson]

It would be sufficient to update their Astros to the latest specs. There's nothing "out of date" about an Astro Saber that's equipped with the latest
host and DSP firmware. However, LAPD is known for being unwilling to update regularly.


Elroy

[escomm]

Do you know what type of radios are being used? If the FD is using 30 watt mobiles, and the PD is using 5 watt portables, I would expect the difference in capabilities. LAPD needs to step up to at least current technology, and drop the old radios. Just my 2 cents...

FD uses 3 watt 800MHz XTS3000s, PD uses 4 watt UHF AS3s.

Low transmit power would only require more receivers, not more transmitters.

The repeaters are all Quantars for PD, I believe the FD has a hodgepodge of MSF5000s and the like.

[escomm]

It would be sufficient to update their Astros to the latest specs. There's nothing "out of date" about an Astro Saber that's equipped with the latest
host and DSP firmware. However, LAPD is known for being unwilling to update regularly.


Elroy

Updating firmware will not eliminate LAPD's need for 14 more transmitters than LAFD

[PhillyPhoto]

Well, I figured LAFD would have some mobiles for extended coverage, and didn't really think LAPD would have astro spectras. Is the DSP upgrades (or lack thereof) due to lack of money, or laziness? I would think they got some money to spend out there, but I could be wrong.

Is PD still VSELP? I know Trenton PD is. I wish they would hop on board the Mercer county 9600 P25 system that's being done up now. Burlington County, NJ and Bucks County, PA are both UHF smartzone, and it would help with the good ol' fashioned "interopobility".

[Elroy Jetson]

LAPD upgraded from VSELP to IMBE several years ago. Their feature package and flashcode changed at the same time, of course.

Elroy

[PhillyPhoto]

LAPD upgraded from VSELP to IMBE several years ago. Their feature package and flashcode changed at the same time, of course.

Elroy

OK, Thanks. Were there any upgrades/additions in radios? Or are they still using just the astro sabers?

[Batwings21]

Escomm, is LAPD trunking or conventional? How bout fire?

[PhillyPhoto]

Escomm, is LAPD trunking or conventional? How bout fire?

Radio Reference is your friend...

http://www.radioreference.com/modules.p ... =RR&aid=37

[Monitor142]

Both LA PD and Fire are conventional simulcast, PD being UHF IMBE and FD 800MHz analog. The sad part is the FD has better PD portables on their rigs (XTS3 and 5K?) than the poor PD does. LAPD finally started installing XTL5k's in new units and some VIP vehicles, but for the most part still using AVA's in the patrol units.

Their stumbling block until the XTL series came out was the need for a true wide band UHF radio for mobile use (480/506MHz). A lot of bad press lately regarding the status of LAPD radios. Expect some creative and emergency financing soon for new portables, lord knows they need them. As others have pointed out, it seems that they were on the reactive end of things as far as the portable maintenance (but that may have been a management issue, not a technician issue).

Brian