Performance expectations when transitioning from analog to digital systems

[ElroyJetson]

This may not be the ideal subforum for this question, but it's best place to pose it that I can think of.

My county is one of the last remaining EDACS holdouts. They are running 99 percent analog voice EDACS with about 1 percent ProVoice traffic,
and maybe a tiny bit of encrypted traffic.

The system is three separate networked simulcast systems which are interlinked.

I don't have the detailed view of system performance that the system's techs do, but from a practical viewpoint, coverage on the fringe areas is decent but it can be noisy at times. We have a substantial length of Atlantic coastline and along the coastline coverage is good for mobile radios, but not so good for portable radios. There are plenty of known dead spots. Generally, it's "abandon all hope" once you cross the dune line.

I hear a lot of noise and distortion in many transmissions. This noise and distortion, when it happens, is heard whether I'm using this radio or that radio or another radio, so I must presume that it's present in the signals received at the sites, by the subscriber units. Describing the noise, I'd say that it sounds like a sheet being ripped slowly more than anything else I can think of. That's a separate form of noise than the type of white noise which is typical of a transmission with a poor S/N ratio which is usually from a portable radio at the fringe of coverage.

I'm even hearing noise in the background when dispatchers are talking, and I presume they're using non-RF voice paths into the system, be it leased lines or VOIP, or whatever...I don't really know, and certainly in the case of the Sheriff's Department this is true. And it changes from transmission to transmission. Some are clean. The next may have a ripping sheet in the background.

What is that ripping sheet distortion? Simulcast distortion? I'd like to hear an example of what that is supposed to sound like.

In general, if I were the system administrator, I'd want an effort to be made to try to improve portable coverage.
I'd also think that they have noise problems that need to be addressed NOW.

At some point, this system is due to switch over to P25 and as I have last heard, it's going directly to Phase II with no stop at Phase I first.
I think that's a pretty bold move. I understand the cost savings in not having to touch every system radio AGAIN but it also seems to me that
there's a benefit to taking it one step at a time.

When they do switch over to Phase II, I have to be realistic and expect the radio techs to be very busy addressing a LOT of problems.

But what I'm getting at, the question I'm taking too long to ask, is, given the description of current system performance, how do you think that the
system will perform after switchover? Are the fringe coverage cases going to get better or worse?

As I'm listening now, I can listen on two simulcast systems. One gives me an RSSI indication of about -103 dBM and the others, about -97. As per the RSSI indicator on my Harris XL-185 portable radio.

 

[GTR8000]

At some point, this system is due to switch over to P25 and as I have last heard, it's going directly to Phase II with no stop at Phase I first.
I think that's a pretty bold move. I understand the cost savings in not having to touch every system radio AGAIN but it also seems to me that
there's a benefit to taking it one step at a time.

There is no benefit whatsoever to deploying P25 in stages, going FDMA first then to TDMA. It's a complete waste of time and money if the system was designed from the ground up as a Phase II system. First of all, if you're spending all that money on the TDMA options for the infrastructure and subscribers, why would you not use it from Day 1? Secondly, there's nothing bold about it at all. Agencies and counties and states have been deploying Phase II systems right out of the box for a full decade by this point, including the Pennsylvania statewide system that has never allowed any FDMA usage. It's par for the course, this isn't 1995 anymore where the technology is unproven.

As for what to expect, well for one thing there's no audible simulcast distortion with P25 as there is with analog simulcast. Yes, there can be multipath issues that subpar receivers and scanners will have trouble with, but the actual subscribers won't have any issues. No background noise as there is with analog on the fringe of coverage. Yes, you may get some bit error (aka "going digital") if the coverage in a certain area is that weak, but generally speaking you can stretch coverage on the fringes a bit more with digital vs analog because of the lack of noise (with all else being equal).

Most of what to expect depends on whether the same subsites will be used, or if new ones will be built to expand coverage. It's almost a guarantee that the antennas aren't going to be booming omnis like the EDACS system probably is now, instead using more focused panels or reflectors especially at the edges of coverage/along county lines.

 

[NVAGVUP]

Another item to ponder is was the EDACS designed/optimized for mobile coverage or portable coverage. Some early trunked sites were built with a single antenna. (Using a duplexer) The talk in coverage on these sites pales in comparison to sites using separate TX and RX antennas with TTA. (At least one vendor recommends 2 RX antennas per site for Phase 2). As GTR mentions, antenna systems will likely change (As well they should if they are as old as the system) Any vendor worth there salt will not stand behind any potential system performance issues if customer chooses to reuse antennas/lines which have been in the elements for years.

The comparators for P25 digital have unbelievable performance vs analog. They literally evaluate the P25 site RX stream bit by bit. Analog comparators toggle between sites. P25 comparators rebuild the P25 stream for the lowest composite BER. (IRIC)

Lastly as mentioned, the biggest system difference is the performance during the lowest signal levels analog vs P25. In analog, anything below ~ 2 microvolts introduces noticeable white noise/popcorn noise. (Which causes uses to request "Please repeat") In the P25 world, those signal levels sound identical until you approach the 4-5% BER level and the users have fewer repeat requests. But zero signal is still zero signal, no matter which modulation is utilized.

Slightly off topic. For users who are in love with the analog "sound" and want P25 to sound the same, it isn't happening. The vocoders in today's P25 radios are fantastic. If the users want a system with greater usable range (RF signal wise), P25 works.

 

[krokus]

I wonder if the noise on the EDACS could be noisy analog components, possibly water/oxidation damage on connections. (Ever hear water damaged POTS lines?)

 

[ElroyJetson]

I wouldn't be in a position to find out but if I worked for the maintenance company, I'd be glad to troubleshoot it and find the problem, and fix it.

 

[MTS2000des]

When our agency was still on a SmartNet .89x analog simulcast during it's "hospice care" years, it was a monthly battle doing mod comps and dealing with MSF5000s that developed tin whiskers in the VCO modules, requiring them to physically be given "concrete calibration" to get rid of hash and trash that would creep up on receivers. The old school Efratom channel modems went pop often. Equipment from this vintage was designed when Reagan/Bush were still in office.

I used to be able to tell what RFSS a subscriber was voted in on by the audio characteristics of the particular receiver/channel bank the inbound audio was getting routed to the "Embassy Ambassador" switch in our CEB room (which is now an office!).

I do not miss this stuff. It was great in it's heyday, but the raw performance of the Astro 25 system that replaced it is impeccable. Watching the new comparator assemble P25 bitstreams from subscribers all over the county with no degradation or audio drops is a sheer miracle. Subscriber radios with crap stubby antennas get in with a DAQ of 3.4 or higher without fail, back on the Smartnet days, we'd get bursts of static and constant comparator swaps of audio from radios with PSMs from the same areas.

A properly implemented and optimized P25 system will MOP THE FLOOR with it's analog counterpart, any day of the week.

 

[kayn1n32008]

...if I were the system administrator, I'd want an effort to be made to try to improve portable coverage.
I'd also think that they have noise problems that need to be addressed NOW.

At some point, this system is due to switch over to P25 and as I have last heard, it's going directly to Phase II with no stop at Phase I first.
I think that's a pretty bold move. I understand the cost savings in not having to touch every system radio

But what I'm getting at, the question I'm taking too long to ask, is, given the description of current system performance, how do you think that the system will perform after switchover? Are the fringe coverage cases going to get better or worse?

It all depends on the RFP coverage requirements are. With out knowing that piece of information, there is absolutely no way to know if portable coverage will improve.

There is ZERO reason to go Phase 1, then transition to Phase 2. Just go to Phase 2 and be done with it. It's not like this is new technology. It's mature amd it's not like this is the first phase 2 syst to be deployed.

You are trying to compare EDACS analogue to a fully digital Phase 2 system. Apples to oranges.

 

[ElroyJetson]

Well, I can tell you, as long as they don't encrypt everything, I'm looking forward to the P25 transition because the average signal quality of the EDACS system is less than admirable. Even some of the dispatch consoles sound fairly bad.

 

[Echo4Thirty]

When our agency was still on a SmartNet .89x analog simulcast during it's "hospice care" years, it was a monthly battle doing mod comps and dealing with MSF5000s that developed tin whiskers in the VCO modules, requiring them to physically be given "concrete calibration" to get rid of hash and trash that would creep up on receivers. The old school Efratom channel modems went pop often. Equipment from this vintage was designed when Reagan/Bush were still in office.

I used to be able to tell what RFSS a subscriber was voted in on by the audio characteristics of the particular receiver/channel bank the inbound audio was getting routed to the "Embassy Ambassador" switch in our CEB room (which is now an office!).

I do not miss this stuff. It was great in it's heyday, but the raw performance of the Astro 25 system that replaced it is impeccable. Watching the new comparator assemble P25 bitstreams from subscribers all over the county with no degradation or audio drops is a sheer miracle. Subscriber radios with crap stubby antennas get in with a DAQ of 3.4 or higher without fail, back on the Smartnet days, we'd get bursts of static and constant comparator swaps of audio from radios with PSMs from the same areas.

A properly implemented and optimized P25 system will MOP THE FLOOR with it's analog counterpart, any day of the week.

PFFFT your old system was luxurious compared to when i came to transition HFD from analog simulcast to Phase II. The simulcast PC was a 286 with the software on 3.5" floppy. Pure bliss designed when Nixon was around.

 

[ElroyJetson]

Does anybody have any concrete data on ProVoice vs analog in an EDACS system, with regard to fringe area coverage?

 

[N4DES]

A properly implemented and optimized P25 system will MOP THE FLOOR with it's analog counterpart, any day of the week.

Absolutely positively... the 813A simulcast was very good, the 7 mixed-mode digital channels made it even better, but the 0598 P25 LSM just rocks my County.

 

[MTS2000des]

PFFFT your old system was luxurious compared to when i came to transition HFD from analog simulcast to Phase II. The simulcast PC was a 286 with the software on 3.5" floppy. Pure bliss designed when Nixon was around.

If I ever see an MSF5000 again, it will be too soon. I cringe when hamsters have this fetish for bringing this era of stuff back to life when modern, much higher quality stations like an MTR2000 or even a lowly XPR repeater, are available for low cost. I know many folks have a soft spot for the MSF...I am not one of them.

 

[Project25_MASTR]

If I ever see an MSF5000 again, it will be too soon. I cringe when hamsters have this fetish for bringing this era of stuff back to life when modern, much higher quality stations like an MTR2000 or even a lowly XPR repeater, are available for low cost. I know many folks have a soft spot for the MSF...I am not one of them.

I site/system owner (Privacy Plus) asked me if I would take over the maintenance on his MSF's until he could transition customers over to a Capacity Max solution. I replied, I'll come out here every now and then and do what I can...which is put a .45 slug into a randomly selected MSF's PA and then go home. He didn't take me up on that...even after I proved letting a Startsite a hundred miles away nuke the Quantro PA's into just exciter power one at a time until the only thing left was the control channel did a great job encouraging customers to transition. This was just a few years ago by the way.

 

[Echo4Thirty]

We had a customer transport one without locking the VCOs. Once I saw it on the crate unlocked, i packed up and left. I did not want to be within 10 miles of that thing. I loathe the MSF...

 

[NVAGVUP]

In the Motorola world of acronyms, we theorized MSR=Micor Simply Repackaged. MSF=Micor Synthesized Frequency.

(MSR's were workhorses. Any problems were straight forward for a good tech) MSF was Moto's first attempt at a frequency synthesized base station and the problems it had were "voodoo" to an old school tech. (EX above. "Whiskers", VCO physical damage is locks were not deployed in transport). If I remember, you had to blow separate PROM's for Freq info and PL info (If multi PL). If you want to maintain an MSF,,,,,,

 

[xmo]

MSF VCO whiskers don't have anything to do with answering the original question:
"Performance expectations when transitioning from analog to digital systems"

From the comments posted, it appears that the consensus is that digital is far superior.

Here's a chart typical of the ones used by all the radio companies to illustrate the digital performance advantage.

If you you were buying a system and the vendor's sales team showed this to you, what would you ask them to provide in the way of proof?

 

[Project25_MASTR]

MSF VCO whiskers don't have anything to do with answering the original question:
"Performance expectations when transitioning from analog to digital systems"

From the comments posted, it appears that the consensus is that digital is far superior.

Here's a chart typical of the ones used by all the radio companies to illustrate the digital performance advantage.

If you you were buying a system and the vendor's sales team showed this to you, what would you ask them to provide in the way of proof?

The answer (as always) is going to be it depends. Going to depend on how the system is designed. Going to depend on the equipment being used now versus what will be used. Just some examples of the factors.

• Many modern radios are far more sensitive receiving digital signals versus analog
• Wideband analog versus P25, analog still has a minor advantage
• System coverage needs have greatly changed over the years
• SU's may not decode CC data as reliably as they do conventional signals (i.e. don't be surprised if a radio that hits 5% BER at -119 dBm doesn't stop decoding CC data at only -109 dBm)

 

[TampaTyron]

Actual coverage shrinks bt 5-10%, but perceived coverage increases by about 10-15% due to no noise/static. It is the complaining about audio quality vs analog that is the biggest pain in my back. This is in my cases trbo vs analog, but still same process. TT

 

[ElroyJetson]

I only had experience with a single MSF 5000 and this was after I had learned "Don't even try to brush the dust off the heat sinks or it'll blow up" so that was an exercise in caution. Fortunately it only needed a replacement power supply. Ebay, 75 bucks later, worked fine. (My boss never did repay me for that....like I care 10 years later.)

Their reputation has kept me from ever wanting an MSF 5000 for myself. I have turned down many, some being offered at almost scrap metal prices.

Meanwhile, there are ancient Motrac era repeaters still in service in this county, amateur repeaters, still slugging it out and winning against everything man, nature, and time can throw at them. Now that's a MACHINE. Heck, even the tube finals are dirt cheap because they're so common. New old stock, in the box, Amperex 5894 tubes, about 25 bucks each on ebay. Service life meaured in decades. Kind of makes you want to turn your back on modern digital equipment because it just WORKS.

 

[GTR8000]

Kind of makes you want to turn your back on modern digital equipment because it just WORKS.

Yeah, let's all continue to operate on ancient 50 year old equipment that is hardly fit for hambone usage anymore. Give me a break.

We've had GTR's dead keyed as a control channel 24/7/365 for 11 years and counting. APX 7000's that were manufactured in 2010/2011 that are still dead balls on frequency operating on TDMA-exclusive systems, which requires a high degree of accuracy as one might imagine.

In conclusion, modern digital equipment that is performing as good as the day it was put into service a full decade later with no tuning or other maintenance required or performed. Buy good equipment, get good results; cut corners and buy junk, wind up spending more in the long run.