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Quantar Preselector Tuning Procedure

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

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ASTROMODAT
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Quantar Preselector Tuning Procedure

Postby ASTROMODAT » Mon Aug 11, 2003 2:09 pm

If there is a Quantar Expert(s) out there, could you please attempt to shed some light on any, or all, of the following issues associated with the tuning procedure of the Quantar Preselector:

1. Why does the UHF Range 2 Preselector tune-up procedure require that the signal generator be set 200 kHz above the Quantar receiver's operating frequency?

2. Should the signal generator be set for FM, or ASTRO25 digital, for purposes of re-tuning the Quantar Preselector? Or, does it make any difference?

3. If one is lucky enough to have access to a Network Analyzer (like Bill Gates and Friends...), is this +200 kHz off-set still required?

4. Does the Motorola Systems Service Center (in Rockford) use a Network Analyzer for this procedure? If so, would one simply send them the Preselector casting (without the RX card) and let them have at it? I assume that the factory new Quantars have their Preselectors tuned via a Network Analyzer?

Thanks for any help you might be able to provide!

Larry

Will
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Postby Will » Tue Aug 12, 2003 2:13 am

Well, the 200hz shift is used in tuning HT1000/MT/MTSX radios also, I can't find much difference.
Usally I just put a receive carrier, un-modulated in and tune the Preselector for best RSSI on the RSS. Keep the signal level low enough to avoid over running the RSSI. Try with and without the 200hz offset. When I think I have it tuned up, I sweep the signal back and fourth thru the channel to see if the signal is centered. +/- 10 khz.

ASTROMODAT
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Quantar Preselector

Postby ASTROMODAT » Tue Aug 12, 2003 1:46 pm

Will, I assume that tuning for best RSSI is not terribly unlike tuning for best SINAD.

In this regards, here is what Mother Motorola states, in big, black, bold letters, in the Quantar Manual (Tab 5, "Quantar Preselector Field Tuning Procedure," page 29):

"Tuning for best SINAD response DOES NOT result in optimum tunig of the preselector assembly. You must use this field tuning procedure to obtain optimum presector performance."

Forgert that---where's that $150,000 HP Network Analyzer?!

Larry

Will
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Postby Will » Tue Aug 12, 2003 2:47 pm

Mother /\/\ may be reffering to a frequency spread and asumes the Quantar is multi freq. For a single frequency receive the RSSI or sinad should work just fine. Only problem I see is that with the digital processing of the receiver audio Sinad may not be the best way as it could be skewed by the DPS. The RSSI comes off before the demodulation and is an indication of received signal strenth. Tune for max RSSI should be right on.

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batdude
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yeah, and here's my spin...

Postby batdude » Thu Aug 14, 2003 6:34 pm

try reading "into" the book when you are taking a Range 2 unit down into the 2m band!

talk about wierd.... i did the 200k tuning 'cause that's what the book said -


thank god the software guys were decent enough not to lock up the software with a hard stop at 150mhz.... i didn't try but my guess is that dead end is about 146.000 or so on a range 2 unit.

i continue to be AMAZED at how scratchy analog signals become crystal clear digital at the edges of the repeater's range.... these quantar guys must be locked away somewhere and only let out on the weekends, because the sensitivity and integration of the entire package is unbelievable....

FYI - when i did the RSS "set squelch" procedure - i could open squelch at about .15 micro-v.... but i went with about 0.18 just to tighten it up a bit.... and to this date, no falsing or drop outs during fringe area repeats.

and

do the fans on the PA only kick on when a termistor tells them to?

i noticed during tuning that my PA fans never came on.... but then again, i didn't dead key it to ToT or anything either...



doug

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xmo
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Postby xmo » Thu Aug 14, 2003 7:41 pm

"...i didn't try but my guess is that dead end is about 146.000 or so on a range 2 unit..."
-----------------------------------------
That's been our experience on several range 2 Quantars - they work fine on the 146 and 147 repeater pairs - but the 145 pairs are just too far out of band.
------------------------------------------
"...i continue to be AMAZED at how scratchy analog signals become crystal clear digital at the edges of the repeater's range...."
-------------------------------------------
Isn't that good clean fun to amaze your friends with how well P25 works!
-------------------------------------------
"... do the fans on the PA only kick on when a termistor tells them to? "
-------------------------------------------
Exactly, they turn on when the PA gets hot.


BTW - send me a PM if you are still trying to sell that high power MSF.

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wavetar
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Re: yeah, and here's my spin...

Postby wavetar » Fri Aug 15, 2003 1:30 pm

batdude wrote:
i continue to be AMAZED at how scratchy analog signals become crystal clear digital at the edges of the repeater's range.... these quantar guys must be locked away somewhere and only let out on the weekends, because the sensitivity and integration of the entire package is unbelievable....

doug


AMEN. Let all the digital bashers out there see this & start to realize what people who actually work with it on a regular basis already know....IMBE digital is as good or better than analog...and it's going to get even better.

Todd
No trees were harmed in the posting of this message...however an extraordinarily large number of electrons were horribly inconvenienced.

Welcome to the /\/\achine.

ASTROMODAT
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Postby ASTROMODAT » Fri Aug 15, 2003 6:16 pm

I think the reason why some folks may be put-off by IMBE is because they are (inappropriately) comparing FM voice quality to P25 digital voice quality (and range performance) in the same sense that analog cellular voice quality is compared to digital cellular voice quality (the latter being one of Tom Leykis's biggest pet peeves!).

While IMBE doesn't currently buy much bandwidth until the next phase of APCO with 6.25 kHz TDMA (FM can go 12.5 kHz narrowband today, like IMBE), cellular implementation of digital took the Cxrs from one anlog talkpath per 30 kHz channel to a MINIMUM of 4 talkpaths of TDMA per 30 kHz channel. And, that's where it started, whereas current bandwidth utilization in cellular is now far better than this. But, as we all know, cellular voice quality sometimes stinks, even when we are in decent range of the serving cell site.

I agree that IMBE currently sounds at least as good as FM, but the real reason for digital is bandwidth conservation (encryption performance is gravy). So, when the utilization of bandwidth issue gets milked hard by the next phase of APCO, we'll have to see how it sounds. I suspect our standard at that time will be to get it to sound as good as the "old" analog FM, but that will be O.K. when we see how much more bandwidth efficient digital is vs/ analog.

Larry


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