Batboard

My agency has a conventional analog radio system as follows:

-MTR2000 analog receiver at a remote site, connected via a leased RTNA phone circuit
-AstroTAC analog receiver at another remote site, connected via a leased RTNA phone circuit
-Quantar P25 capable repeater (a transmitter and a receiver) at headquarters building
-JPS/Raytheonn SNV-12 analog voter at headquarters building.

The JPS selects the best of the three analog received signals (2 remote + 1 local) and sends it back out the Quantar transmitter (i.e. the Quantar is programmed as a base, not a repeater, since the JPS does the "repeating").

The above infrastructure is all narrowband analog capable, but wouldn't support P25. However, could I add a DIU-3000 between the JPS and the Quantar transmitter to make the system output (just the output, not the input) be P25?

I'm thinking ahead to the day (not that far away) we switch/reprogram the system to narrowband. Narrowband reduces range. I'm not too worried about our talkin performance, as our remote sites are in pretty good locations. We could tolerate a reduction in talkin performance.

I am a little more worried about talkout however. Since all of our mobiles and portables are P25 capable, I could reprogram then for analog transmit and mixed mode receive. That way, theoretically, the P25 would help to offset the talkout range reduction caused by narrowbanding.

So, everything coming in would be analog. It would be analog voted, and then the best analog signal would be digitized by the DIU-3000 and sent to the Quantar transmitter. The dispatch console audio would also pass through the DIU-3000 and be digitized.

Would this work?

I think you'll need to add the V.24 card and change the controller in the Quantar so it can xmit Astro P25. I don't know if a Quantar can do mixed-mode (rx clear analog, xmit P25). The DIU is the correct device to act as the gateway for the analog rcvrs and console converting them to V.24 that would get to the Quantar via digital grade leased lines. Theoretically your plan might work. Should be bounced off someone with more experience than me. I don't think you are really going to lose any range going narrowband analog, or make up for it going P25 xmit.

I shouldn't see why not, I'm thinking the Quantar would have to be programmed for "Astro Only" and not mixed mode.
Just a question though, what is your in-cabinet repeat fall back plan should you loose all of your receivers?

Mark

The static [bench] sensitivity [RF signal level for a given SINAD or 20 dBq] of narrowband analog FM radios is often equal to that of wideband ones. This leads some to conclude that there is no penalty involved in converting to narrowband. Not so.

Wireless communications system performance [coverage] is designed today using the concept of Delivered Audio Quality [DAQ] - a subjective metric that has a scale from 1 to 5 where 1 represents unintelligible and 5 means speech is easily understood. DAQ-3.0 equates to speech understandable with slight effort, occasional repetition required due to noise / distortion. DAQ-3.0 or higher is often used as a minimum requirement in system design [and in system RFP's].

In the real world [faded sensitivity], the narrowband analog FM [+/-2.5kHz] format requires an additional 3dB of signal to provide DAQ-3.0 as compared to the wideband [+/-5kHz] format. On the other hand the C4FM - IMBE format requires 4.8 dB less signal to attain the same DAQ-3.0 than does wideband FM. This means that there is a delta of almost 8dB of improvement that could be obtained with adlertom's proposal. [These dB differences are based on published VCPC parameters for the respective formats - converting from Cf/(I+N) to RF carrier level by adjusting for receiver ENBW]

How well that 8dB will translate to YOUR real world will depend on your users - how they perceive IMBE audio quality versus analog and how they react to the brick wall digital edge of coverage versus the 'softer' drop-off of analog systems.

XMO, thanks for the detailed explanation.

Bill, I've read some white papers and also talked to Motorola engineers about the coverage difference between wideband and narrowband. The general "best guess" I had heard (prior to XMO's post) is that going to narrowband is equivalent to a 6dB reduction in signal strength. With analog narrowband, as the deviation gets less, the quieting/ability to overcome noise gets less, the capture effect gets less, and audio recovery becomes more difficult. They say that going digital may mitigate some of these issues. As XMO says, it does depend on the system however. There may or may not be a noticeable difference.

Mark, I'm not sure. The Quantar RSS doesn't clearly delineate the receiver vs. transmitter programming. Our Quantar is already P25 capable, but I'm not sure if setting the modulation mode to Astro Only would effect both TX and RX. In the RSS, on the channel information tab, there are modulation setting choices of "Analog", "Astro CAI", and "Analog/Astro CAI". I'm guessing the latter setting would be the one I want. It's a live system however, so I'm hesitant to play with it just to find out.

As for in cabinet repeat, I decided to leave that turned off. I was concerned that, should the JPS voter fail, the system would keep working on the in cabinet receiver and nobody would notice the problem. At least with in cabinet repeat disabled, the failure would be obvious and service would be called immediately. We have a backup base on the talkaround channel that dispatchers and officers are instructed to switch to in the event of a main system problem.

adlertom - Have you considered a prop study of the system to see if it needs, and where it needs, enhanced coverage?

We have gotten tremendous reports back from customers using Mototrbo. People have grown used to "digital audio" because of cellphones. Their expectations are suitably trained to work with bubble and chirp instead of hiss and noise. They definitely love the additional building penetration and extra range they are experiencing. I can't say for sure what you will experience with a hybrid system, or what limitations you'll run into with the various mobiles and portables. I would expect some bump and grind. But, it would be excellent if you could make it work.

Bill_G wrote:adlertom - Have you considered a prop study of the system to see if it needs, and where it needs, enhanced coverage?

We have gotten tremendous reports back from customers using Mototrbo. People have grown used to "digital audio" because of cellphones. Their expectations are suitably trained to work with bubble and chirp instead of hiss and noise. They definitely love the additional building penetration and extra range they are experiencing. I can't say for sure what you will experience with a hybrid system, or what limitations you'll run into with the various mobiles and portables. I would expect some bump and grind. But, it would be excellent if you could make it work.

Yes, we did have a propagation study done. It was worthwhile, and we even moved a receive site based on the predictions. The study did show less talkout range than talkin, which I already expected (our headquarters building/transmit site are in a low lying area). That's why I'm more concerned about talkout. I think our talkin is robust enough however to tolerate some reduction in performance due to narrowbanding.

Additionally, our analog JPS voter is new and I'd rather not replace it with a digital voter (along with digital connections to the two remote receivers) if we don't have to.

So, that's why I'm considering this hybrid analog in/digital out approach.

I've also heard good things about Mototrbo performance, but we have a large investment in P25 mobiles and portables. We won't be changing those anytime soon.

Prop studies are great sanity checks on a system. Almost an essential tool these days. Takes the guess work.

I wasn't suggesting Trbo over P25 for public safety (grant requirements and interoperability), but backing up your conclusion that digital would improve your outbound coverage. I have been very impressed with performance though I went into it with a lot of doubts. Customer feedback only reinforced my confidence. It's a good step forward in technology.

I would be interested in seeing the outcome of this as well.

I have a Quantar that I would like to set up to operate in in-cabinet digital repeat mode, but still allow it's external digitac to key it in analog mode and operate as a wide-area voted analog repeater.

Issues I'm having are with getting RX audio out of the receiver while the station is keyed up in digital mode (status tone, et al.)