Repeater help..

[Motoballa]

I recently purchased a Motorola CDR700 UHF Desktop Repeater, complete setup, duplexer and all, the seller and I agreed it would be a fully functioning non-DOA purchase, so I don't intend on returning it unless the issue I have cannot be fixed easily

The first issue I ran into was no audio coming out the transmit side. You could key up and talk all you want but nothing would come out except dead carrier, so I returned the repeater to original programming although that didn't work, next I played around with some settings and figured out one of the options was set wrong, that was fixed. Easy.

Next problem, the repeater literally goes like 50 yards down the road then dies. My first thought and I've dealt with this before is perhaps the PA blew. So, I switched out the controller cables from each radio as well as the cables to the duplexer. Did a test, still goes the same distance, I think it's very unlikely the PA is blown on both radios, so that leads me to the next idea.. Well, I don't have an idea on what would be next. Has anyone had this issue before and can lead me in the right direction?

Some more info that may be helpful: I am using 75 foot of brand new LMR400, output power is 20 watts, duplexer is properly tuned, antenna is a 1/4 wave mag mount.

Thanks in advance, 73s.

 

[mmckenna]

Couple of questions….

How do you know the duplexers are tuned correctly? Are you taking the word of the seller?

New LMR-400 likely isn't the issue if it's not damaged/wet, etc. But long term outdoor exposure might be a problem.

Mag mounts don't make me feel all warm and fuzzy. Likely not an issue, but worth doing an SWR check.

Check the power output using a respectable wattmeter.

The 50 yard range either is de-sense due to the mobile type duplexer not tuned to your frequency, or the PA is blown. Without some testing, it's hard to call.

 

[Motoballa]

Yeeeeah I'm going by word of mouth from the duplexer being tuned. The last time that thing was programmed was actually from Depot software a while ago, so assuming a dealer programmed it which would make me think it was only programmed once, and thus anything on the repeater was touched once.

Although maybe the duplexer was moved around or whatever and the screws came loose etc. I have a friend willing to tune it for me but that would be a couple of months, it is free though but I'm sorta in a rush to get this thing up and going. Let me try something else when I get home and report back. Thanks!

 

[KevinC]

Does the RX radio receive further than 50 yards? This will take 2 people and some other sort of communications to test, but without test gear you can't do much more.

 

[FKimble]

Where is the 1/4 wave mag mount antenna located? Attached to what and how high? Anything metal near the antenna?

Frank KK4YTM

 

[mmckenna]

Yeeeeah I'm going by word of mouth from the duplexer being tuned.

Until you check it, you'll never know. Guessing it was done to your frequency pair probably isn't the best approach.

The last time that thing was programmed was actually from Depot software a while ago

Or someone just downloaded depot from some Russian website….

, so assuming a dealer programmed it which would make me think it was only programmed once, and thus anything on the repeater was touched once.

I'd suspect anything and everything at this point. As was said, until you get some proper test equipment on the entire system, everything will be a guess.

Although maybe the duplexer was moved around or whatever and the screws came loose etc. I have a friend willing to tune it for me but that would be a couple of months, it is free though but I'm sorta in a rush to get this thing up and going. Let me try something else when I get home and report back. Thanks!

It's probably got the mobile notch filters. Easy to tune if you have the right equipment. Easy to screw up if you don't. While they do have a bit of slop room, they will need to be tuned specifically for the frequency pair you are using. Unless the original user was using the exact same frequency pair, or they can show you they were tuned for your pair, I'd mark them as suspect, too.


I'd stop trying to use it if it's not performing right. Without test gear, you could be setting yourself up for problems. If the duplexer is tuned incorrectly, you can create some high SWR issues that might create some issues.

Also, if you plan on using it long term, you'll need something better than LMR400. While it will work, you can get issues with the dissimilar metals in the shielding. That can lead to all sorts of issues.

You need to check the TX output.
You need to have the duplexers checked to see if they are on the frequencies you need.
You need to check the receiver.
You need to eventually replace the coax and the antenna.

 

[kayn1n32008]

The 50 yard range either is de-sense due to the mobile type duplexer not tuned to your frequency, or the PA is blown. Without some testing, it's hard to call.

I would lean more to the duplexer being the issue, rather than a blown PA. Even if it is only exciter power, it should transmit more than 50 yards.

Locally we have had some repeaters have their PA’s go south(one was an MSR2000 another was a was an Icom) Even on excited power, I have been able to use them from 10-20km out. Super weak signals on receive, but useable. Especially on UHF out on the flats around Edmonton.





Sent from my iPhone using Tapatalk

 

[mmckenna]

I would lean more to the duplexer being the issue, rather than a blown PA. Even if it is only exciter power, it should transmit more than 50 yards.

Locally we have had some repeaters have their PA’s go south(one was an MSR2000 another was a was an Icom) Even on excited power, I have been able to use them from 10-20km out. Super weak signals on receive, but useable. Especially on UHF out on the flats around Edmonton.

Yeah, I had an MSF5000 do that after the cell carriers working on the tower damaged the coax. Worked well enough that our fire department wasn't really noticing much of an issue unless on the fringes.

I think you are right, the duplexers are likely to blame, although I don't know how much power a CDM would put out with a dead PA into a mal-tuned duplexer into 75 feet of coax to a 1/4 wave mag mount.

 

[crazyboy]

Yeeeeah I'm going by word of mouth from the duplexer being tuned. The last time that thing was programmed was actually from Depot software a while ago, so assuming a dealer programmed it which would make me think it was only programmed once, and thus anything on the repeater was touched once.



Although maybe the duplexer was moved around or whatever and the screws came loose etc. I have a friend willing to tune it for me but that would be a couple of months, it is free though but I'm sorta in a rush to get this thing up and going. Let me try something else when I get home and report back. Thanks!

This makes it sound like the duplexer was never retuned. The duplexer has to be tuned to your pair, even if it was already tuned movement during shipping could have detuned it.

 

[Project25_MASTR]

This makes it sound like the duplexer was never retuned. The duplexer has to be tuned to your pair, even if it was already tuned movement during shipping could have detuned it.

I’ve also seen some duplexers become untuned the second power was applied to them. In other words, tuned with a tracking gen, hooked up and found to not be working, put back on a tracking gen only to be discovered its way off from what it was tuned to.


Sent from my iPhone using Tapatalk

 

[kayn1n32008]

I think you are right, the duplexers are likely to blame, although I don't know how much power a CDM would put out with a dead PA into a mal-tuned duplexer into 75 feet of coax to a 1/4 wave mag mount.

Duplexer is where I look first, then feedline and antenna, then power output.

Also make sure none of the connectors are damaged.

I have never heard of a repeater not usable at such a short distance.

Even with a bad connector, we were able to get almost 2km out before we noticed a problem.


Sent from my iPhone using Tapatalk

 

[RadioGuy7268]

Duplexers allow you to transmit and receive through a single antenna. Try splitting your antenna system.

If you're in an all-fired hurry to determine what's wrong, but you have no test equipment, consider getting a separate antenna for the transmit side - and just run 2 antennas for a test. Use your one antenna with 75 ft. of cable to go directly into the receive radio, then wire up a 2nd antenna to the transmit radio. Keep a minimum of 20 ft. vertical separation between the transmit and receive antennas.

If you can't get a good mile or so with that simple setup, you've got a radio/programming problem. If it starts acting like an actual repeater now, you'll need to go spend some money & get your duplexer actually tuned to your exact frequencies.

Cheap, fast, reliable, easy & repeaters are words that rarely go together.

 

[N1GTL]

OP: What test equipment do you have? SWR meter? Dummy load? Service Monitor?

I think you can get some good suggestions here if everyone knows what you have to work with.

 

[crazyboy]

I’ve also seen some duplexers become untuned the second power was applied to them. In other words, tuned with a tracking gen, hooked up and found to not be working, put back on a tracking gen only to be discovered its way off from what it was tuned to.


Sent from my iPhone using Tapatalk

Well that is interesting!

Just so the rest of the gang here knows, this was purchased from me. The two CDM’s were aligned on a calibrated R8100 at the end of 2017 and the repeater was then placed on a shelf as the project never took off. It was sold as working, but no programming or tuning was included.

 

[mmckenna]

Well that is interesting!

Just so the rest of the gang here knows, this was purchased from me. The two CDM’s were aligned on a calibrated R8100 at the end of 2017 and the repeater was then placed on a shelf as the project never took off. It was sold as working, but no programming or tuning was included.

Thanks for chiming in. That's sort of what I figured was going on.

 

[Motoballa]

Thanks for all the feedback guys and gals.

So, I was looking at the duplexer and for some odd reason the TX was on the high and the RX was on the low, so I swapped those and bam! It goes like, almost a mile down the road, then drops. So I think I've fixed it? The pair is 444.7375+ so I'm not too sure why the connectors we're out of place, this whole repeater just needs to be taken apart and put back together the correct way

I left it on the pair they had the duplexer tuned to so I could get the most out of it, the 1/4 is on top of my bedroom door about 8ish feet up, so the next test is to take it out back and plop it up as high as I can.

I'm still convinced there is a small issue with the limited range, although it is only 8 foot up and with the loss through the LMR so. It maybe working perfectly. I shall report back with my results during the next testing.

 

[Motoballa]

Well that is interesting!

Just so the rest of the gang here knows, this was purchased from me. The two CDM’s were aligned on a calibrated R8100 at the end of 2017 and the repeater was then placed on a shelf as the project never took off. It was sold as working, but no programming or tuning was included.

Just saw this, this is why I shouldn't have assumed or I should've asked. I'll see if I can get my friend to tune it.

Thanks.....Crazy...

 

[mmckenna]

Thanks for all the feedback guys and gals.

So, I was looking at the duplexer and for some odd reason the TX was on the high and the RX was on the low, so I swapped those and bam! It goes like, almost a mile down the road, then drops. So I think I've fixed it? The pair is 444.7375+ so I'm not too sure why the connectors we're out of place, this whole repeater just needs to be taken apart and put back together the correct way

I left it on the pair they had the duplexer tuned to so I could get the most out of it, the 1/4 is on top of my bedroom door about 8ish feet up, so the next test is to take it out back and plop it up as high as I can.

I'm still convinced there is a small issue with the limited range, although it is only 8 foot up and with the loss through the LMR so. It maybe working perfectly. I shall report back with my results during the next testing.

That would certainly explain the issues you've been seeing.

 

[paulears]

I'm still somewhat confused by what is going on.

You are using the frequency pair the duplexer was tuned for yes/no?
Your antenna is presenting a 50Ohm, resonant load yes/no?
You are using the duplexer the right way around yes/no?

One thing you could do is remove the duplexer, and insert a ¼ wave length of wire into the RECEIVE antenna socket. Even with the desense, you should get a 200-300m range out of the system.

Don't forget that the duplexer needs everything to be matched - a load other than a resonant antenna skews the performance badly. Repeaters are tricky to set ups properly. My own one is down on range due to desense at the moment. All I have done is swap to a spare antenna while I fix the feeder on the other. They are not plug and play, and they really, really hate rubbish antenna systems - which frankly, is what a quarter wave on top of the door is!

 

[hitechRadio]

The pair is 444.7375+ so I'm not too sure why the connectors we're out of place, this whole repeater just needs to be taken apart and put back together the correct way

The 1/4 is on top of my bedroom door about 8ish feet up, so the next test is to take it out back and plop it up as high as I can.

Mobile Reject Duplexers do not take well to a mismatch at the antenna port. Your mag mount quarter wave I can on top of your door is not going to work. Maybe contact the seller that chimed in here, and see if he can sell you an antenna better suited to your needs.
Also have the duplexer tuned.

As far as taking it apart, I would leave it alone. As I am not so sure you know what the correct way is.

Sounds like your headed in the right direction, just lacking some antenna knowledge which plenty here can help with.

You need to get an SWR meter, or a friend with one.