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Author Topic: Qantar's or MTR3000's  (Read 173 times)

K6ECS

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Qantar's or MTR3000's
« on: October 24, 2019, 05:18:51 PM »

 I need your help on this one gentleman. And ladies. We have three sites that are all running MSF5000s on VHF. They have a 30KHz front end. We did try the commscope kit that was supposed to make it a 15 khz front end when in reality it makes it 12.5 and the audio sucks! It's time to replace them.

This issue has been batted around and sidetracked so many times that I really need your help staying on track and that means me as well. We are on a frequency that the pair has been reversed. We have a stations output on both sides of our input very close to us. We actually have to detune to keep the other repeaters that are in compliance from taking out our input. That means losing valuable sensitivity. We do have chip angle dual bandpass cavities but they're only good for + / - 500 khz. We get it.

I have a couple of CDM 750s that have a 20 khz front end. They're both rated at 80dB adjacent channel selectivity at 20 khz. I have a 200 W repeater amp and I would have to run the CDM at damn near nothing to get close to our coordinated power output. I truly believe in playing fair. I have numerous Arcomm controller's laying around and could easily throw together a repeater. They all have actual auto patches and RTC clocks in them. I even have the 19" rack mount. But given the fact that Heaps Peak in Southern California has high output FM transmitters and dirty VHF paging transmitters that have given us issues in the past I'm really hesitant to go this route. The only other option is to use a Quantar or a newer MTR 3000 and both only have a 25 khz / 12.5 khz.

Presently, due to our location which gives us a nice figure eight pattern we are able to cover all of Southern California and most of the high desert from one machine. We have two others that basically act as fill-ins and are voted using Allstar. I realize that if we go to an MTR3000 we will have the option of going to DMR. But if we stick to analog we can keep our Allstar/IRLP/Echolink and in the event of an emergency anybody would be able to access the system. There are pros and cons. I know that we can't vote DMR anyway. I also know that will lose about 20% of our coverage area because of timing issues.

So then the issue becomes since we can't switch the pair because of one individual on the pair doesn't want to go along with it just to be difficult, but another does - there are three of us that if we open the squelch can hear one another - we're stuck having the outputs of two popular repeaters on our input. 25 khz doesn't seem like it's going to be better than 30 khz but not by much. But then again I don't know the quality of a Quantar or a MTR3000.

To save us all headaches, without getting into the root cause of our problem which we cannot change and there is no filter narrow enough to knock out a station 15khz away, which would you go with. The older quantar or the newer mtr3000? Or would you take the cdm's that will do 20 khz with 80 dB adjacent channel selectivity and go that route? I mean it would be cheap enough to try. It's closer to the 15khz band plan we have in Southern California. I don't know of any other radios that will do it since the 1250 and the 1550 both have lower adjacent channel selectivities.
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KB8VUL

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Re: Qantar's or MTR3000's
« Reply #1 on: October 29, 2019, 05:20:40 PM »

You are asking a question I will not answer.  I like them both, but I like them both for different reasons.  And each of them has some weaknesses as well. 
Quantar
Getting very old in the tooth.  If you get one.  Get one with the fan in the face of the power supply, not the one with the heatsink in the face of the power supply (the ONAN supply) The Onan supply when they get old they fail very drastically, with blue fire out the front.  When it happens the power supply is done.  Non-repairable, burnt traces off the board done.  I have supported over 100 of these units that were 800 Mhz.  The Power supplies are sort of fail prone, but with the number of 800 units floating around used good supplies are available,,, stock up if you get a Quantar. 
I personally am a fan of C4FM (Astro digital or P25).  I have never replaced an exciter or receiver in a quantar.  Been working on them for over 10 years, way past their end of life.  PA's do fail, but are typically repairable.  If you go this route,,, be damn sure what you are getting.  Get a copy of the correct part numbers for EVERY piece of the unit and verify ALL of it.  The SCM (Station control module) is key to it operating.  There were several and only some of them would allow for standard analog repeat.  Also make sure that the range for all the modules match.  A range 2 VHF amp and a range 1 exciter will NOT work together.  And moving then from range to range is an undertaking.  Some fools are piecing these together for spare parts and you may end up with different range modules if you are not paying attention.  Range 1 is for ham VHF.  There are 3 ranges that are common for UHF... range 2 is for UHF.  Range 1 is 403 to 433 and range 3 is 470 to 520 so you don't want either one. 
Try to get a v.24 card, and an astroTac or SpectraTAC if you want them to vote.  And v.24 links back from RX sites are possible but require some Cisco smarts to make happen.  And the links will be Ethernet. 

MTR2K /3K units.
Range info applies to these as well.  Know what you are getting
3k's will vote DMR.  You can vote DMR with the right software and some old 8300/8400 repeaters with a firmware upgrade.  It's done over Ethernet as well but sin't as complicated.  They will also connect to a JPS or Doug Hall voter as well for analog voting.  Audio link are needed and I will leave that up to you how that happens but again, Ethernet links are your friend and only require being purchased once and don't have reoccurring costs like having Internet to each site.  EchoLink and the like are possible with DMR, but you do it with a control station and not directly into the repeater.

Both have Mixed mode ability,, but the DMR mixed mode requires a license from Motorola.  The Quantar P25/ analog is native to the SCM.

Now as far as your receive issues.
First option is a pass can that is very tight.  I would slip it in between the duplexer and the receiver.  Yes, you will have insertion loss of about 3db but if you are having innermod issues and it's effecting the receive, fixing the issue by degrading the receive by 3 db is an acceptable method in the commercial radio arena.  3db on receive isn't as much as you think.  And the only signals you are going to be missing were not very good to begin with.  Beyond that is a crystal filter, but those are expensive and fragile, they will not take a surge well at all.  Again, place it after the duplexer. 
You may be able to cheat if you have several sets of duplexers sitting around.  Steal a single receive can off another set and put it in line of the set you have.  And while we are talking can's, what sort of shape are the ones you have?  If they are some old set of whatever, that are 30 plus years old, they may need rebuilt.  The tuning slugs are silver plated in most of them and can be cleaned up with silver polish.  The finger stock can be cleaned up in a similar fashion.  But you will need to take them completely apart to do it.  So tread lightly if you are unsure how to do this type of work. 

As far as the MSF kits.  The RX bandwidth is pretty much based on the IF filter you used in the kit. 
The kits were to convert a wideband radio to narrowband.  And yes if you are running 25Khz signals through them they are cutting off a good bit of signal and causing the audio to sound bad.  One option is to find the correct IF filters for 20Khz and install them in the receivers.  That would address your issues.

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K6ECS

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Re: Qantar's or MTR3000's
« Reply #2 on: October 30, 2019, 01:00:36 AM »

Thank you for time spent putting together a detailed reply. For someone who says he's not going to decide you did a pretty good job of cutting down the middle. I am more inclined towards the Quantar. The only reason I thought of the mtr3000 is that it's newer. I don't want to go to the DMR repeaters and I'm not sure about the newer Motorola repeaters. I do know that on the brandmeister system voted sites on DMR don't work according to them. Right now I have tremendous range from my location. I mean I really have tremendous range. I really don't want to give it up to DMR and timing issues.

I'm aware of that Crystal filters exist and the easier solution would be just to reverse the pair back the way it's supposed to be. That's issues with the coordination body and one user who is now pissed because he moved and in direct line of sight to my repeater that's been up longer than his. " I didn't know you were repeater covered so well here." Maybe he shouldn't have moved his repeaters without authorization from the coordinators. Prior to that we were friends and he was willing to reverse the pair which meant all three of us on the pair would be in agreement and the coordinator could not really deny it. Nix that idea. I don't want to have to induce loss but if I have to then I have to.

On the msf 5000 the IF is 30khz VHF. The band plan is 15 khz. You can see how that doesn't work. The commscope kit was supposed to cut it down to 15 khz but actually cut it down to 12.5. The audio was terrible. We had to revert back to the 30 khc and detuned slightly giving up receive coverage due to the other long-standing repeater that puts in a -22 dbm signal an our repeater site from a hundred miles away. They are running a db224 or aimed right at us and we are running a db224 aimed right at them. Not to harm each other. But because we're trying to hit downtown Southern California. It just happens that we are in direct line of sight. We're at 6500 feet and their it only 1,700 feet. There's nothing between us. It's not worth re-litigating it's been going on for 10 years. I don't personally know of any filter capable of rejecting a signal 15 khz away add only 3 DB loss. If you could give me a name I'd be happy to look it up.

Currently sites are voted using all star. We want to RF link them. With California being fire-prone and earthquake-prone ethernet is not the solution. I'm a network administrator and I know that in the event of a catastrophic event the internet's going down which means our links will go down with it. They'll be of no use to us then. The repeaters our course will operate a stand-alone repeaters. They're all on the same frequency with the same output PL.

Thank you again. As I said I'm leaning towards the quantar but for the very reason you brought up checking each module when I see them on eBay I wonder if they are Frankenstein's. I know to buy the gold cage ones because they have the better power supply. I just don't know that I can trust eBay. I've been burned too many times.I'm
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KB8VUL

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Re: Qantar's or MTR3000's
« Reply #3 on: October 30, 2019, 09:52:32 PM »

One thing I can't help but mention, and it would seem to help you both.  Have you ever considered true simulcast?
You would basically mirror the repeaters, and link them.  Same transmit and receive with same PL.  It would HAVE to be a group thing though. 
The quantars would be great with this, but you would need the spectratac comparators and channel banks to do it, along with higher end GPS to set the launch times for the audio.  Your coverage footprint would be unreal, like the systems of back to back repeaters you sometimes hear about that are reverse or each other and can cover the better part of a state. 
MTR2000
Quantar
and MSF5K units will all do it, but the MSf's had to have it as a factory option, my guess is that yours don't.

As far as the co channel issue, If you were there first, then it may be time to push back at the coordinators.  You can only do so much with technology and that is not gonna get fixed with any reasonable tech. 

Specifically addressing the 15Khz away signal.  Yes, I am assuming it's on your input.  A sharp pass can will bring it down some.  But you are gonna get a 3 db loss.  If you are hearing so well that you have a -22 signal coming in from the distance you mentioned, either the other end is running WAY over 100 watts, or you have a hell of an antenna system.  I wouldn't be concerned with even 6 db if you can hear like that. 

I would do some testing though.  Get someone with a standard 35 watt mobile and portable to go to the far end of the area you want primary coverage in. Take your repeater off the air and have them transmit on like normal on the input frequency while you look at the real signal level in a service monitor.  Document those numbers and then do a receiver sensitivity test for the 12 db sinad receive.  If the signal level difference is greater than 6 db then you are safe with than much loss in a filter to address the signal filtering.
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KB8VUL

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Re: Qantar's or MTR3000's
« Reply #4 on: January 13, 2020, 08:21:28 PM »

After reviewing this, I wanted to add a couple things.
As far as Ethernet links, I should have specified microwave links with Ubiquiti or some similar IP radio link, not Internet.
Another thing to consider, considering your HAAT, is an antenna with down tilt.  Be that electrical or physical (tip the mount ) towards the area you are trying to cover and away from vertical.  That may make some difference.  And the other guy may want to do this as well as he's at 1700 feet plus, if you can get him on board with the idea.  It would give you both better coverage into the town below and less coverage to the horizon.
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