Bad Duplexer?

[hockeyref2]

I bought a new motorola SLR5700 repeater and 'motorola' DSCP10725 mobile duplexer from a large national dealer to replace a Motorola XPR8400 repeater. UHF, IG band.

I kept hearing static and had poor reception/range issues with the new system on both analog and DMR. After lots of troubleshooting (3 repeaters, 2 duplexers, 2 sets of jumpers, 2 different antenna systems, 3 different antennas (2 unity gain, 1 3dbd gain), running 10-20 watts output) I narrowed it down to the duplexer.

What could cause this type of issue?

 

[alcahuete]

What could cause this type of issue?

A really rough time during shipping, not being tuned properly in the first place. The dealer did tune it, right?

 

[mmckenna]

Mobile duplexers tend to suck.
If it's not tuned well, desense can really impact performance. Did you have someone check it on site, or did you rely on a dealer setting them up and mailing them to you?

 

[MTS2000des]

yep. a mobile duplexer on a repeater like that is like driving around in a Tesla on spare tires with low air.

a proper 4 cavity "for real" full size duplexer like a Telewave TPRD4544, will actually work and give you decent isolation. Depending on RF environment, a circulator may also be needed.

 

[Ubbe]

Nothing wrong in using that 6 cavity duplex filter. It's a Procom duplexer (or is it a Cellwave?) that have been used at numerous repeaters.

Can the repeater be put into analog mode and then run it against a dummy load instead of the antenna and then use a 30dB-40dB inserter at the dummy load, perhaps just a T-connector and a 30dB-40dB attenuator where you connect a signal generator and key the repater and adjust the filter for maximum output and best sensitivity. It should be no, or barely detectable, degradation of sensitivty when the repeater is keyed.

The coax to the antenna and the antenna in itself could be problematic so use an antenna analyzer to check those.

It could also be interference from another transmitter at that location. Then check coax and antenna and for external interference by just substituting the dummy load for the coax to the antenna and check sensitivity when the repater are keyed while connected to the outside antenna.

If you have access to a check VNA it can be used to check the coax/antenna and can sweep the filter while you check if it's coarse tuned properly in all cavities and then do the final tune with the live system and antenna.

If the repeater cannot be switched to analog mode then it is a bit more uncertain to adjust the filter and have to be done just by a VNA sweep and then VNA check the coax/antenna.

/Ubbe

 

[MTS2000des]

Nothing wrong in using that 6 cavity duplex filter. It's a Procom duplexer (or is it a Cellwave?) that have been used at numerous repeaters.

Sure, if you don't care about performance.

 

[Ubbe]

That Telewave are only two cavities for TX and two for RX, and the OP's duplexer have three for each TX/RX. The difference are power handling at 250W for the Telewave but no problem with a 25W repeater for the OP's duplexer and it's good for up to 40W, so that repeater should not be running at full otput of 50W.

/Ubbe

 

[hockeyref2]

Thanks for all the replies!
Yes, I relied on the dealer to tune it and ship it. It appears to be in good shape physically.

It is an combilent 6 cavity. I am in a rural area and I don't believe there is much going on in UHF. The problem is 'always' there so I don't think its some interference. (the working one is a celwave)

The problem moves with the duplexer, and I tried it on two completely different antenna systems in different parts of the plant, and with different repeaters..

The repeater is setup in mixed mode but we use analog. I cant get people to use the RSM's properly in analog... DMR would be a disaster - we are a manufacturing plant with people in very loud places.

I don't have the expertise (and probably budget) to get all that fun test equipment so I get to rely on the out of state large dealer with some 'free' or 'moderately priced' help if I ship them things (Hooray for corporate contracts?). Or I can call in a local people. With COVID they frown upon bringing in outside people unless its mission critical.

 

[MTS2000des]

You really need to get a baseline on what your noise floor is, with and without your filtering system. A spectrum analyzer on the uplink of the repeater for 24-48 hours in log/capture mode is a start. Then PM the repeater and ensure it's not part of the problem. Then a proper sensitivity test with an iso-T.

Keep in mind, your tuning of your duplexer is affected by physical shock of transit. It really should be done on site when it's in the environment it's going to be used in, with the antenna/feedline it's going to be connected to.

I would consider having a functional communications system in your plant to be "mission critical", so a qualified vendor should be able to resolve your issues. It does require specialized test equipment, and someone with experience (please don't take this personally). Repeaters aren't plug and play like consumer electronics devices such as wireless routers/access points, and it does take someone with experience and the right tools to sort it out.

 

[WA0CBW]

There are a lot of mechanical things that could be defective. Check all the connectors (especially the TX, RX and Antenna ports) for dirty or expanded or missing "fingers" on the female connectors.
Bill

 

[prcguy]

The last service call I did on a mountain top I had a customers complete repeater with duplexer in my shop and it was tuned to perfection and working great. I drove up the nasty trail to the 5,000ft hill and installed everything and it worked like crap. Fortunately, besides my service monitor I brought my spectrum analyzer with tracking generator and found the duplexer was all out of whack. A quick tune up on the hill and everything was perfect again and the customer commented they have never seen the system work that good with hand helds.

Duplexers do not like vibration and I would expect one to go out of tune being shipped across the country. Its just what they do.