Nucleus to Quantar Conversion?

[Jonathan KC8RYW]

Can someone please confirm or deny that a Nucleus paging base station can be converted into a Quantar base station capable of IMBE?

[123]

I would like to know as well.

[d119]

It really wouldn't surprise me in the slightest.

I have a DSS III here that's been converted to a mixed mode Quantar with V.24 wireline and DIU, works fine. Only difference on the backplane is that one of the 10 pin header connectors isn't populated. Traces & through-holes for it are there, but the connector isn't. Big whoop anyway, I've never seen them used even on Quantar stations.

Though the thing that makes me think it may NOT work is that the Nucleus could accept two PA's and two power supplies. I'm not sure if that would cause a problem or not. It would take a once over of the two backplanes visually to tell you if it will or will not work.

Does the Nucleus even have a backplane connector for a wireline card? I think the metalwork on the rear of the Nucleus is different, is it not?

I can say this much though: The 120VAC power supplies are interchangeable between Quantar, DSS III and Nucleus stations. I found that out first hand when a customer was jammed up with a bad Quantar power supply and a working Nucleus, I took a chance and downed the Nucleus to bring the Quantar back online, and it worked.

[n7maq]

Here is what one has to go thru just to pass FM voice http://www.repeater-builder.com/motorol ... ticle.html


All of the following is pure speculation, I have not worked on any Nucleus transmitters, only Quantars . If I'm wrong or right I hope that someone who knows for sure will correct me or confirm it. The station backplanes are totally different so you would have to use a Quantar backplane, and even then I doubt the QTAR SCM would even talk to the NUC boards.


I assume the NUC will TX flat audio so perhaps you might be able to set up the poor mans P25 repeater and instead of using a second Maxtrac as your TX you could use the NUC.


Jim

[desperado]

First off, there is not flat audio in a NUC.
It's designed specifically for paging and not any sort of audio, so that will need worked around.

Also, be aware that a Quantar looks at firmware on all the modules in the station.
Swapping the control board and receiver into a NUC from a Qtar isn't going to work most likely.
The codeplugs are different and I assume that significant modifications to the plug would be necessary to get the unit working correctly.

A note on power output and the Nuc, the company I work for supported some paging transmitters that were 1KW output.

Duplexers for 1KW would be hard to find if they even exist.
Bear that in mind if you have a 1KW NUC transmitter.
The receive would need to be remote and with that pwr level you would most likely need multiple receive sites to overlap receiver coverage with transmitter coverage.

[willbartlett]

So, Having played with some of this, here is what I know:

You can port all of the boards from a 900 quantar (analog only) minus the 100w PA into a 300w NUC frame, and it will try to repeat. RX works fine, the exciter will attempt to tx, but the SCB doesn't know what to make of the 300w PA and second power supply in metering, and as a result, you get a PA fail warning, you'll never get it to repeat at 300W.

I have also used a 300w frame and backplane with a single power supply as a testbed to verify basic board functions on other quantar boards. no surprise here, the backplane is band independent.

Also have moved a 25 watt vhf pa and r2 exciter into a low power nuc frame, along with a R1uhf rx and you can do silly cross band repeat stuff this way. I've also put 900 rx modules into the vhf exciter/pa setup and the same holds true.

My take is that for ham use, no harm can come from this, but a pox on any who think of doing this for commercial use.

Will

[desperado]

OK, so you are transplanting a Quantar controller, receiver and exciter / PA kit into a NUC chassis and it is working without alot of effort.
That's interesting.

Are you indicating that the NUC exciter and PA will work with the Quantar SCB? I think that's what you have said but I want to clarify.

I know of a Quantar that someone threw together with a low split VHF PA and a high split exciter, it tests good in alignment mode but will NOT TX when enabled as a repeater.
I am assuming that it's due to the miss match. NUC parts are easier and cheaper to get than Quantar parts and it may be n option.

I was under the understanding that a NUC exciter will NOT do analog audio, are you indicating that it does?
Also, what if any CAI / Astro testing have you done with the NUC parts in the unit?

[n7maq]

I was under the understanding that a NUC exciter will NOT do analog audio, are you indicating that it does?
Also, what if any CAI / Astro testing have you done with the NUC parts in the unit?

The article that I posted a link to goes into detail on using the Nuc as a repeater, and yes they will pass analog audio fairly easily.


Jim

[kcbooboo]

The Nucleus exciter will indeed pass audio. However the only audio path deals with what would be called VCO Modulation (VCO MOD). It's missing the other path called Reference Modulation. The REF MOD is needed for the low frequencies (DPL and some PL) because the synthesizer and VCO will try to correct for low-frequency changes and essentially cancel DPL and PL signals. With the REF MOD present (as it is in the Quantar exciter) the reference oscillator is modulated as well, so the VCO doesn't know the low freq signals should be corrected for (cancelled) and the board ends up with proper modulation.

I compared the two Nucleus exciter boards I have to the Quantar exciter board and schematic. The parts that deal with the REF MOD signal are NOT present on the board. There are probably two dozen resistors and capacitors and a couple of diodes that would need to be added to pass that audio signal to the synthesizer. You'd then need to provide a second audio signal to the exciter. In the Quanter, these two signals (REF MOD and VCO MOD) come out of the station control board and one or both have level-adjust pots on them. The ratio needs to be adjustable so DPL comes out properly (square and with low distortion). On other stations this might be called Modulation Compensation.

The MaxTrac used for audio processing in the above-mentioned article provides both VCO MOD and REF MOD signals, however only the VCO MOD was used because that's all the Nucleus exciter has circuitry for.

Of course, this only addresses the audio issues; I'm sure there are other differences.

Bob M.

[willbartlett]

The Nucleus exciter will indeed pass audio. However the only audio path deals with what would be called VCO Modulation (VCO MOD). It's missing the other path called Reference Modulation. The REF MOD is needed for the low frequencies (DPL and some PL) because the synthesizer and VCO will try to correct for low-frequency changes and essentially cancel DPL and PL signals. With the REF MOD present (as it is in the Quantar exciter) the reference oscillator is modulated as well, so the VCO doesn't know the low freq signals should be corrected for (cancelled) and the board ends up with proper modulation.

I compared the two Nucleus exciter boards I have to the Quantar exciter board and schematic. The parts that deal with the REF MOD signal are NOT present on the board. There are probably two dozen resistors and capacitors and a couple of diodes that would need to be added to pass that audio signal to the synthesizer. You'd then need to provide a second audio signal to the exciter. In the Quanter, these two signals (REF MOD and VCO MOD) come out of the station control board and one or both have level-adjust pots on them. The ratio needs to be adjustable so DPL comes out properly (square and with low distortion). On other stations this might be called Modulation Compensation..

Agreed on all of this.

I picked up a R2 nucleus exciter and 25 watt PA and am in the process of modifying it to a quantar by reverse engineering from schematics. I have it passing P25, but the levels are a little low. I believe the P25 mod is handed in through the refmod chain, but I haven't confirmed any of that yet. some of the components I used are off in tolerance or a closest match in value, so it's not factory. I'll put together a mouser order soon and do it the right way.

Will

[desperado]

OK, a bit off topic, but it seems that you have enough knowledge to answer this question.

As I mentioned before, I know of a Quantar that was assembled from parts that has a mismatched Exciter and PA
one is low VHF the other is high, can't remember which is which right now.
This keeps the unit from operation (or at least that's the assumption).

What differences in the hardware (other than RF tuning parts) that let the SCB see what it's looking at?
I am hoping that it's some jumper matrix on the board as opposed to a firmware difference that could be modded so that it all matched up.

Thanks in advance.

[willbartlett]

Yep, In all of the exciter and PAs I've looked at, at least VHF ones, it's a resistor array feeding a mux that gets reported back to the SCB. In the exciter, it's one resistor to change the reported range, and in the PA, it's either the addition or removal of a couple of resistors to change it. Then there's the RF components and their effect on performance, but that's another issue altogether.

I'll add that all of this is spelled out pretty plainly in the service manual for the quantar and quantros. I have the manual with the schematics, which are fine for component location, but there's absolutely NO board art included. Amazing. I haven't seen many of the newer MOT manuals, but compared to a Maxtrac, Spectra or Micor manual, this leaves quite a bit to be desired. Even the original Astro and XTS manuals were quite a bit more detailed.

I know that MOT intended for the Quantars to be module replacement repair based, but it's kind of a shame to exclude some more advanced theory.

Will

[desperado]

Thanks for the info.
After finding that out, I took a look at a Quantar Service manual and found what you were talking about.

After a few changes, it's up and working.

Thanks for the nod in the right direction.

[markfguibord]

Has anyone successfully converted a Quantar UHF R1 to UHF R2?

I'm Looking for detailed instructions for doing the conversions.

Thanks,
Mark

[Jonathan KC8RYW]

What I'm wondering is if one could take a Nucleus and, even with much tinkering, turn it into a P25 repeater. No analog audio at all.

[willbartlett]

You could but the list of modifications is longer than the maxtrac flat audio mod.

IF you could build or a reliable 4 level decoder, AND implement the FEC, AND cleanly apply that to the modulation input for the exciter, you would be most of the way there. but you're talking about building a decoder, FEC and data reclock, and modulator. That's not quite rocket science, but the required knowledge and experience to pull that off from scratch is BSEE or better. if you were interested in doing the flat audio trick with a nucleus, there's no reason it shouldn't work, but why bother with a Nucleus. I'd opt to work with an MSF or MSR. The work to get flat audio in and out of an MSR is already fairly well documented. MSF shouldn't be too much different. I'm waiting till somebody uses an MSF for Dstar.

As for he R1 to R2 change, most of the components are surface mount filtering components, inductors and capacitors, but the VCO modules are going to be pretty tough to beat. If you were to change the range ID resistors and programming, the VCO would be trying to make RF where it was never intended to. It looks like it's similar to a spectra style VCO, with stripline components that were laser tuned at the factory. At the band edges you might get lucky, but beyond that I suspect it's SMT rework time. Probably a couple caps and the stripline work, but there is zero documentation on that VCO module. It's treated as "magic occurs here" in the service manual. Getting the module off the board, and then getting under the can would be fun too. hot air table and microscope.

I look forward to doing that someday, I'm pretty confident I could do it. I already have a R1 RX. Anybody have a R1 exciter they want to donate to science? Only half kidding.

Will

[desperado]

OK, lets take this a step further.
I have a VHF Nuc with a UHF analog receiver in it.
I also have a VHF astrotac remote receiver.

As configured it will pass analog audio VHF to VHF or UHF to VHF, but what about pulling the V.24 audio off the astrotac and feeding it to the exciter's flat audio input?
Is that going to work for AstroCAI or no??