Duplexer Problem? Motorola GMRS Repeater

[linboogy]

Hello to all and thanks for taking the time to read this!
I have recently purchased a Motorola RKR1225 repeater and had it pre programmed for GMRS. It did not come with a duplexer, so I purchased one of the 6 cavity 50 watt Chinese ebay duplexers and had the seller tune it to my high/low frequencies. I am using an Optek UH2401 6.5 DB gain antenna about 25 feet off the ground on a chimney mount.

Here's the issue I am having
After testing, I am only getting a spotty 3 mile radius of range. I have used a Jetstream UHF SWR meter and got the SWR down to 1.2. The repeater has been turned down to 25 watts. I hooked the meter to test everything after the duplexer and the SWR is still the same but the power dropped down to 15 watts. If I bypass the duplexer, the wattage goes back up to 25 watts. I have switched the jumper cable around with the same results.
Sorry for the long post but to sum it all up, I believe I have a problem being that the duplexer is dropping my wattage from 25 watts to 15 watts and the repeater only works about a 3 mile radius hit or miss. If I use my mobile radio in my vehicle, I can hit it maybe 5 miles away but really shifty.
Any feed back or ideas would be appreciated.
Thanks in advance

 

[nd5y]

Can you have somebody with real test equipment verify the power levels and that the duplexers were really tuned properly?
What is the insertion loss spec on the duplexers?
The difference betwen 15 and 25 watts is about 2.2 dB. That isn't much and could be normal.
Those are some pretty small diameter coax jumpers. What kind is it? Are they the proper length?
Are you using the same type coax from there to the antenna?

 

[jim202]

Have a few questions to help in the investigations of what might be your problem.

The first question is what make and model is the feedline that is going to the antenna?

Second question is what is the coax that is being used for the jumpers at the duplexor?

The third question I need to ask is have you listened to the repeater input frequency to see if there may be any signals or noise there on the receiver?

I haven't taken the time to look up the information on what the specs should be on the duplexor. You will see some loss from the transmitter output going into the duplexor and what you see going to the antenna coax on the output of the duplexor.

The last question to ask has the repeater receiver been put on a service monitor to see what the actual receiver sensitivity is.

Without having a full understanding of what all the total aspects are of the repeater, it is a pure speculation at this point. Your going to have to supply much more detailed information for any of us to help.

 

[popnokick]

In addition to the above: What is your ground and lightning protection system? Check all of those connections, and if you have a cartridge type lightning arrestor (most are) ensure the cartridge in the arrestor is good. Nearby lightning strikes can pop the cartridge with no other apparent damage. Even if the system hasn't been through a lightning storm yet, can you say for certain it's a brand new cartridge in good condition? I discovered mine had been damaged by lightning.... after my repeater dropped it's range to about 1/3 of what it was. Replaced the cartridge... all OK now.

 

[linboogy]

Thanks for the response
The small jumpers are Motorola and that's all I seen stamped on them. I have checked them with a fluke meter and have no measurable resistance. They are the ones that was with the repeater and have N to mini UHF connectors. The coax going to the antenna LMR400
I have no test equipment other than a Jetstream UHF meter. The RX has no noticeable interference.
I am very surprised I would get this kind of a loss and assumed there was a problem. The repeater has a 1.5 second hang time and when I was testing it around the city, that is how I was going about it.
I have none of the test equipment you mentioned.
There is another large scale GMRS repeater here in Cincinnati. I can try to see if anyone can lend me some testing equipment

 

[kayn1n32008]

While 2.2db of loss is not the worst I have seen, if the site you are at has one high(25+w) power transmitters above 450MHz, dump that garbage mobile duplexer and find a proper pass/notch duplexer, like a Sinclair Q3220E Res-Loc. Spec'd at 0.8db(very realistic with these) insertion loss, and minimum 75db(90+ easily achievable IF you have the dynamic range in the test gear)isolation @5MHz separation. I can think of dozens of repeaters here in Alberta that use them.

Also dump the LMR-400 in favour of some hardline. Regardless of length. LMR-400 is not good to use in full duplex service.


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[DMRAPX]

How many feet of LMR 400 are you using.What kind of distance do you get using just a 25 watt radio,meaning without the repeater and duplexer in line.

 

[linboogy]

How many feet of LMR 400 are you using.What kind of distance do you get using just a 25 watt radio,meaning without the repeater and duplexer in line.

About 48 feet of coax. I previously used a Motorola CDM1550 20 watt with several miles of range. Tested up to 18 miles unreliably. The antenna used to be side mounted to the house. I have raised the antenna since to the chimney now that I found a buddy that has a bucket truck. I am up rather high on a hill as well.

 

[linboogy]

Here are the specs of the duplexer
:

- 50W RF power Handling
- 6 cavity Design
- Minimum Tx and Rx frequency difference: UHF 5Mhz
- Maximum Tx and Rx frequency difference: UHF 20Mhz
- Power Isolation >75dB
- Power loss <1dB
- Easy to build your repeater
- Support Frequency: UHF 380-485Mhz
- N connector
- Fit for Motorola Repeater Enclosurer
- 2.0Kg
- 15.5cm x 22cm x 3cm

Package contents:

- 1x 50W UHF duplexer with N connectors

So it looks like it should only be 1 db of loss. As far as the coax goes, I was under the impression that the 400 was acceptable for a small setup like this. What do you mean by hard line?

 

[prcguy]

I think the average through loss of a 6 cavity mobile duplexer is around 1.5dB and you will have a few 10ths of a dB more loss with the jumpers shown in the pics. 2.2dB is excessive and if I'm reading your first post right you did something to get the SWR down, then checked again after the duplexer and the SWR was the same. Did you try to check SWR between the repeater transmitter and duplexer? Did you touch any of the adjustments on the duplexer?

As others have said this repeater system (all components) needs to be tested individually to see where the problem lies. Owning a repeater without the proper test equipment and knowledge to test and align it will turn out to be a very expensive project when you have to rely on other professionals to do the work for you.

For kayn1n32008, I can see pushing a Sinclair duplexer if your in Canada, eh, but in the US I think the best of the bunch would be a Phelps Dodge/Celwave 526 series, which can be had for maybe $150 used on a really good day. However if the repeater in question is not at a repeater site and far away from other transmitters, a mobile duplexer can give reasonable results. And as others have said, the LMR400 should go in favor of 1/2" Heliax for a run of 25ft or larger for a longer run.
prcguy

While 2.2db of loss is not the worst I have seen, if the site you are at has one high(25+w) power transmitters above 450MHz, dump that garbage mobile duplexer and find a proper pass/notch duplexer, like a Sinclair Q3220E Res-Loc. Spec'd at 0.8db(very realistic with these) insertion loss, and minimum 75db(90+ easily achievable IF you have the dynamic range in the test gear)isolation @5MHz separation. I can think of dozens of repeaters here in Alberta that use them.

Also dump the LMR a-400 in favour of some hardline. Regardless of length. LMR-400 is not good to use in full duplex service.


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[DMRAPX]

Well,i just went through everything you are doing.You get what you pay for.I went through 3 x 6 cavity mobile duplexers before buying a Sinclair Res-Lok Q3220E duplexer.I was using 70' of LMR400 before changing to Andrew Heliax LDF4-50A 1/2" .Then i bought a better antenna, a Comtelco BSL450XL6-C.
Made a big difference.

 

[linboogy]

Thank you all for the help so far. Very knowledgeable people on here.
I wish I had access to some testing equipment. I have read about these duplexers and they seem to have overall good reviews for a small system. I realize now that everything needs to be tested together though. I am going to have to find someone to physically help me from this point I guess.

 

[techman210]

Likely, you have a desense issue. Can you disable transmit, and go past your 3 mile distance, and still be heard clearly in the local speaker? That would indicate most likely a duplexer issue, and radio issue second.

Making sure the SWR from the antenna system is close to 1:1 is also important. Large mismatches at the duplexer will influence duplexer resonance. There are plenty of threads here that detail the problems with LMR cable in duplex service.

 

[linboogy]

Likely, you have a desense issue. Can you disable transmit, and go past your 3 mile distance, and still be heard clearly in the local speaker? That would indicate most likely a duplexer issue, and radio issue second.

Making sure the SWR from the antenna system is close to 1:1 is also important. Large mismatches at the duplexer will influence duplexer resonance. There are plenty of threads here that detail the problems with LMR cable in duplex service.

The TX is just as bad. I know that because I was listening to the 1.5 second hang time and the end tone of the repeater. If I cant find someone with equipment locally to help me, I am going to try to buy a original duplexer that would have come with this repeater and get it retuned

 

[kayn1n32008]

I think the average through loss of a 6 cavity mobile duplexer is around 1.5dB and you will have a few 10ths of a dB more loss with the jumpers shown in the pics. 2.2dB is excessive and if I'm reading your first post right you did something to get the SWR down, then checked again after the duplexer and the SWR was the same. Did you try to check SWR between the repeater transmitter and duplexer? Did you touch any of the adjustments on the duplexer?

Agreed, the only other suggestion would to be to make sure the jumpers are odd multiples of 1/4wave length. ie: 1/4, 3/4, 1-1/4.

As others have said this repeater system (all components) needs to be tested individually to see where the problem lies. Owning a repeater without the proper test equipment and knowledge to test and align it will turn out to be a very expensive project when you have to rely on other professionals to do the work for you.

200% Agreement here. With 2.2db of loss see if you can find someone with the equipment to check the tuning of the duplexer. As prcguy said, the insertion loss is a bit high.

For kayn1n32008, I can see pushing a Sinclair duplexer if your in Canada, eh, but in the US I think the best of the bunch would be a Phelps Dodge/Celwave 526 series, which can be had for maybe $150 used on a really good day.

Well I will always suggest options that work, and are of the best quality. On that note there are two companies I rarely see in the used market. Sinclair Technologies is one, and Daniels/CODAN are the other. These companies are kinda the opposite to Motorola... You may pay less, but you will not find better!



I have put one 'Maxtrac mobile special' repeater in service, that is outputting 12.5 watts into a 20+ year old Q3220E, that is outputting over 11w into about +/-120m of 20+ year old 7/8" Alucell(sp?) hardline with a 20+ year old omni configured 30SD335-HF2PALDF equivalent Sinclair antenna. We get minimum 60KM range but can be worked out to over 90km due to terrain.

There is a reason I suggest Sinclair Technologies and it is not just because they are Canadian. It is because they build a top notch product they will stand behind that will still be there 20+ years after you put it into service.

However if the repeater in question is not at a repeater site and far away from other transmitters, a mobile duplexer can give reasonable results.

Agreed.

And as others have said, the LMR400 should go in favor of 1/2" Heliax for a run of 25ft or larger for a longer run.

prcguy

Heck for any run in full duplex service.

You get what you pay for.

You sure do!

I went through 3 x 6 cavity mobile duplexers before buying a Sinclair Res-Lok Q3220E duplexer.I was using 70' of LMR400 before changing to Andrew Heliax LDF4-50A 1/2" .Then i bought a better antenna, a Comtelco BSL450XL6-C.
Made a big difference.

We put a couple repeaters up using mobile duplexers, they all got switched out, even at low RF density sites. It truly does make a big difference.

Thank you all for the help so far. Very knowledgeable people on here.

I wish I had access to some testing equipment. I have read about these duplexers and they seem to have overall good reviews for a small system. I realize now that everything needs to be tested together though. I am going to have to find someone to physically help me from this point I guess.

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[kayn1n32008]

The TX is just as bad. I know that because I was listening to the 1.5 second hang time and the end tone of the repeater. If I cant find someone with equipment locally to help me, I am going to try to buy a original duplexer that would have come with this repeater and get it retuned

Save your pesos for either a Cellwave like prcguy suggested, or a Res-Loc... Don't waste your time or money on anything less.

One questions, did you buy the duplexer pre-tuned? If so did you verify they tuning before you put it in service? I have read threads where folks bought the mobile duplexers from China(not totally a bad thing, I have benched tuned them and they can tune up and meet Sinclair or Cellwave mobile duplexer specs, they are just a bit more painful to do due to cheap tuning rod design) pre-tuned, but we're way out of spec when checked before installation.


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[rescue161]

I bought one of these Chinese duplexers and they tuned it for free. I put it on the service monitor and it was tuned, but showed a high insertion loss, which was right around where your is. I tried my best to realign it and only got it slightly better.

Go with a real BPBR duplexer and you will be much happier. You can also find 50 foot rolls of 1/2 Heliax on Ebay for cheap.

 

[rfradioconsult]

When you ordered your duplexer did you specify the EXACT transmit and receive frequencies you are using? Sometimes folks using GMRS frequencies will order a duplexer for a specific frequency pair then change to another pair. The duplexers are pretty narrow and don't take kindly to being operated on a different frequency pair than they were tuned to.

LMR400 is ok for simplex operation but when used for duplex operation (ie repeater service) the design of the cable can cause IM products on the receive signal. For the length of cable involved a run of quality RG-8 such as Belden would be just fine.

 

[linboogy]

When I ordered the duplexer, I gave them specific TX and RX that I am using. They even wrote the frequency on the high and low ports. I never touched any of the tuning screws. I can tell the screws were adjusted because of the paint marks but there is a nut to keep them locked into place. I was very leery of going the Asian route "no offense intended" but was reassured by some reviews that the most notable problem with them was that they may cause slight interference with a close frequency. I don't have any equipment to test the duplexer but at this point, I think I am going to start by replacing it first. I also contacted the seller of the duplexer to let them know the amount of wattage loss. If its only supposed to be 1 db, I still think it has a problem or was falsely advertised.

 

[linboogy]

I was considering this Motorola MSF5000 100 watt UHF duplexer.
I found someone to tune it as well for a fee.