UHF Repeater coverage problem

[Nextgentow88]

Hello all im having an issue with a new repeater install on top of my shop. I cant get more than about a half mile away in any direction with a handheld starts getting static and about a mile or two in any direction cant hear or be heard. I cant figure out what the issue is. Here is all the details if anyone can give me a clue.

Frequencies Rx 466.662 Tx 461.662

Vertex vxr-9000 repeater 50w uhf running at 10w into amplifier.

Tpl Amplifier 9 watts in 110 watts out

Tried two duplexers first rfs 50 watt mobile flatpack notch duplexer without amp only rated for 50w input. Second Dbspectra DSBCDUP02CA milled window filter with built in rx amplifier and isolator using with tpl amp 108 watts in getting about 68 watts out of duplexer.

Feed line wilson superflex lmr400. All jumpers are 1/4 heliax or rg400.

Antenna is andrew db404-b 4 element dipole antenna omnidirectional gain 3.5dbd/5.9dbi vertical beamwidth 27° mounted on roof about 35ft above ground level.

I tried swappping out a few things but keep getting same result. Only thing i have not tried is switching the repeater and the feed line. The line is brand new lmr400 i know its not good for duplex service and will be changing it but i dont think it would cause such a drastic issue like this.

Any other info needed please let me know. Really want to get this working correctly.

Thank you all for taking the time to look at my post.

 

[mmckenna]

Have the duplexers you tried been tuned on site, or did you have them tuned by someone else and shipped to you?

Yeah, LMR cable isn't a good choice. If it is totally dry, it can work, but a bit of moisture and it'll cause issues. Replacing that ASAP is a good plan.

 

[prcguy]

I see a number of potential problems but I suspect duplexer tuning is your main problem. A flatpack mobile duplexer can work at maybe 25w if tuned properly. Yours may not be tuned properly. LMR400 should never be used in a full duplex system like in the antenna path. You can get away with an LMR400 jumper from the transmitter or receiver to the duplexer but not in the common path because its known to cause IMD in the system raising the noise floor.

The DB Spectra duplexer is an odd one with a rated 3.5dB loss. Its a window type duplexer for use with frequency agile repeaters or as part of a multiple combined repeater system. Probably not a good choice for what you are doing. Especially trying to run 100+ watts, that takes some expert work in assembly and tuning to make it all play nice.

Last is turning the 50w repeater down to 10w to feed an amplifier. That might be out of spec for the repeater and many repeaters or transmitters will produce lots of transmitter garbage that can interfere with the receiver, desensing it when turned down too far. Then you add an amplifier that will boost all that garbage making the problem that much worse. I have a Yaesu repeater that will do 50, 20 or 5w. It has problems at 50w and will burn itself up at that level. Its ok at 20w and at 5w its transmitter trashes out its own receiver. Your Yaesu repeater could be a big POS like mine is.

To remedy your problem I would first turn down the repeater to maybe 25w and have the flat pack duplexer tuned by an expert on site since transporting them and bumping them around after tuning can change the tuning. Then test the repeater and flat pack duplexer in full duplex mode on a service monitor to see if any desense is detected. Then and only then would you connect it to an antenna. But before connecting to your antenna replace all the LMR400 with non PIM cable like Heliax. If the repeater and duplexer performed ok on a service monitor then it should work fine on the antenna with Heliax. With 25w into a flat pack duplexer you should get about 17w out to the antenna and that should be plenty to do a distance check with handhelds or mobiles.

Your DB Spectra duplexer with 3.5dB loss seems kind of silly to me because if you feed it 100w you will only get about 45w out to the antenna. Not a huge improvement over 17w and you will also have the same 3.5dB loss on receive where the flat pack equipped repeater will probably hear a little better. If you think you need more power I would get another duplexer with at least 85dB isolation, 100dB is better and it may only have 1.5dB insertion loss so your 100w amplifier would get closer to 70w out to the antenna.

Since you are using hand helds that 70w isn't going to do much for you if the hand helds can hear the repeater at 30mi but they can't get back into it past 5mi. All that extra power is potential interference to the repeater receiver and it takes top notch equipment and alignment to make it play together. Just remember to test any repeater and duplexer configuration on a service monitor full duplex BEFORE connecting to the antenna, otherwise you will be chasing your tail for eternity.

 

[Nextgentow88]

Thanks for the reply prcguy

The flatpack dupexer was tuned by a reputable shop that does a ton of county equipment nycocom in poughkeepsie ny. The dbspectra is a 6000 dollar duplexer tuned by them it would be a big let down if it wasnt spot on. I tried turning the power down on the flatpack to 25 watts getting same results. The vertex repeater has a low 10w med 25w high 50w setting.

The dbspectra is sold with the motorola gtr8000 100w repeater. It has a max of 14db return loss excuse my typo lol idk where you seen 3.5db. From what dbspectra says there milled filter duplexers are superior to the normal bpbr can filters idk? I read it to be true but i have no experience with them. I lose about around 40 watts with it 108w in 64w out. I would have much less loss with a regular bpbr duplexer i know that for sure. So at the antenna im guessing its somewhere around 40 watts. Hopefully ill have a telewave 4544 4 can by the end of the week. The lmr400 i know is a no no but its all i had at the moment 1/2 heliax is ordered. Thanks again for the input im going to give it a shot with the telewave and heliax if that does not work something had to be wrong with the repeater.

 

[KevinC]

Thanks for the reply prcguy

The flatpack dupexer was tuned by a reputable shop that does a ton of county equipment nycocom in poughkeepsie ny. The dbspectra is a 6000 dollar duplexer tuned by them it would be a big let down if it wasnt spot on. I tried turning the power down on the flatpack to 25 watts getting same results. The vertex repeater has a low 10w med 25w high 50w setting.

The dbspectra is sold with the motorola gtr8000 100w repeater. It has a max of 14db insertion loss idk where you seen 3.5db. From what dbspectra says there milled filter duplexers are superior to the normal bpbr can filters idk? I read it to be true but i have no experience with them. I lose about around 40 watts with it 108w in 64w out. I would have much less loss with a regular bpbr duplexer i know that for sure. So at the antenna im guessing its somewhere around 40 watts. Hopefully ill have a telewave 4544 4 can by the end of the week. The lmr400 i know is a no no but its all i had at the moment 1/2 heliax is ordered. Thanks again for the input im going to give it a shot with the telewave and heliax if that does not work something had to be wrong with the repeater.

I would imagine it has 14 dB return loss, not insertion loss.

 

[Nextgentow88]

Yes return loss too much dam loss lol

 

[KevinC]

And 108 in and 64 out is about 2 dB loss. You need to do a desense test to see how the RX is. And of course sweep the antenna system.

 

[Nextgentow88]

Thanks everyone for the replys i think im going to bring it to the shop tomorrow and have them give it a look over.

 

[vagrant]

You need the shop to sweep and tune it at your site.

 

[Nextgentow88]

Weird datasheet

 

[jeepsandradios]

461.662 is not a frequency either. I assume you meant 461.6625. Not that that fixes your issue but documentation wise make sure you have the correct. Additionally you also need to fall into your license. If your ERP is only 25 watts you are overbuilding the system. You also didn't say how much LMR you were using. 100' is 3db of loss so 50 in is 25 out.

 

[prcguy]

The DB Spectra duplexer covers a very wide band without retuning and within its operating range its not really any better than any other good quality cavity type duplexer on a single frequency. The DB Spectra comes with a two port hybrid combiner and if that's disconnected the insertion loss will be less. Bottom line is if you have any major brand of 1/4 wave cavity type duplexer with 85dB or more TX-RX rejection, your repeater should work fine into a service monitor. I would consider the antenna system separate and a DB404 antenna fed with appropriate size Heliax should get you down the road a ways.

In my experience with a repeater and antenna on a second story building in an urban area at sea level I could get about 5mi reliably to a 50w mobile and maybe two miles to a handheld. In some directions I could get 35mi or more to a 50w mobile but it was spotty. In this case the repeater was operating perfectly into a well tuned duplexer with about 35ft of 1/2" Heliax into a DB420 with close to 10dBd gain, quite a bit more than a DB404 so under the same conditions expect less range with a DB404. Repeaters should be on high hills or mountain tops to get good range.

Thanks for the reply prcguy

The flatpack dupexer was tuned by a reputable shop that does a ton of county equipment nycocom in poughkeepsie ny. The dbspectra is a 6000 dollar duplexer tuned by them it would be a big let down if it wasnt spot on. I tried turning the power down on the flatpack to 25 watts getting same results. The vertex repeater has a low 10w med 25w high 50w setting.

The dbspectra is sold with the motorola gtr8000 100w repeater. It has a max of 14db return loss excuse my typo lol idk where you seen 3.5db. From what dbspectra says there milled filter duplexers are superior to the normal bpbr can filters idk? I read it to be true but i have no experience with them. I lose about around 40 watts with it 108w in 64w out. I would have much less loss with a regular bpbr duplexer i know that for sure. So at the antenna im guessing its somewhere around 40 watts. Hopefully ill have a telewave 4544 4 can by the end of the week. The lmr400 i know is a no no but its all i had at the moment 1/2 heliax is ordered. Thanks again for the input im going to give it a shot with the telewave and heliax if that does not work something had to be wrong with the repeater.

 

[spanky15805]

mmckenna, prcguy please expand on lmr being a problem.

 

[KevinC]

mmckenna, prcguy please expand on lmr being a problem.

I’m neither one, but “braid” type of coax in a duplexed system can cause passive IM.

 

[mmckenna]

Yeah, its the tinned copper braid over the aluminum foil wrap. Dissimilar metals makes for a non-linear joint and makes for IM.

If everything is dry and perfect, it'll usually work well enough. Introduce moisture, corrosion or anything impure and it all goes to hell.

Heliax is the right stuff to use.

 

[prcguy]

Times LMR and equivalents have a tinned (copper?) braid over aluminum foil shield. The dissimilar metals can produce low level IMD in the presence of high RF levels which can be received by the repeater receiver. Its not a problem with just a radio feeding an antenna but a repeater transmitting and receiving on the same feedline can have its receiver interfered with from the IMD.

mmckenna, prcguy please expand on lmr being a problem.

 

[spanky15805]

Thanks guys. It never dawned on me about the dissimilar metals.

 

[12dbsinad]

Setting up a repeater always needs to be done on site. There could be a multitude of issues and it's possible it has nothing to do with the duplexer or everything to do with it. Could be localized issues causing very high noise floor, who knows. Money would be best spent sending a good tech out to do a system check and dial in what the issue it. Dealing with RF and full duplex is like going on your first date with a women, you just never know what you're gonna get until you field test her.

 

[rescuecomm]

Three different techs including me tuned a VHF duplexer for a guy. All of us were told we didn't know what we were doing. I went to the site and hooked a WT and a Bird 43 to the antenna. SWR was varying from 1.3 to 3.8. Antenna had a cracked base and moisture in it. 12db is correct - go up there with test gear.

 

[TampaTyron]

What type of jumpers between repeater and duplexer (pre-made or shop/customer built)? Is the LMR400 pre-made or terminated on site? Is the antenna mounted in the clear (no metal or other items near the radiating elements)? Was antenna and coax swept with something other than a wattmeter? Was the frequency checked for activity prior to activation of the repeater? Based on complaints, it is likely a duplexer tuning or coax/connector failure or antenna near a metal object. TT