retuning duplexers ??? why ???

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n0wjh

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i adgee that there is never any reason to retune duplexers ....there is a guy in the ham club that wants to retune the duplexers
so question is what symptoms would we have if they did need to be retuned ???
the repeater transceiver is down for repair however
we tested them with a handheld seems to work fine to me ...
thanks terry n0wjh
 

mikewazowski

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How long have they been in service? Can't hurt to go over them using proper equipment if they've been in service a while.

Not sure how you tested them with a handheld? A good tech will use a tracking generator and a spectrum analyzer to tune them.
 

n0wjh

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retuning reply

about 10 years in service ...well we didnt have any other way to test the duplexers onsite so we disconnected the repeater radio and used a handheld to replace the repeater radio it as a simple test
the repeater probably had a surge that took out front end of the receiver and we needed a simple test also damaged the phazing lines on the db224 antenna ....
the coax HARDLINE was checked by the radio station engineer and is good
the antenna is up 400 on a commercial tower so it isnt easy to get to last climber said that it was pitted from lighting strikes can we assume perhaps the phazing lines need to be replaced
also .....
again lacking any other way to test the antenna we used the handheld to test it would transmit and was hearable about 10 miles away it WOULDNT HEAR ANYTHING not even the weather service broadcast that was hearable without the rubber duck antenna ........( handheld --adapter --to coax-- to -hardline -to db224
is this a viable test ????
we couldnt think of anything else easy to do
the repeater has been slowly been degrading until the last perhaps lighting strike ???
that took out the front end ....any ideas we are really struggling with this this repeater has been down down for a about a year causing many problems and endless unfruitful discussions at the club meetings
thank you in advance terry N0WJH
'
 

jim202

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To expand on what Mike has said, you need to ask yourself just why you think the duplexer needs to be messed with. Sure it's the heart of any good operating repeater, but someone playing with it can kill a functional repeater also.

There are good duplexers and there are poor duplexers. Their operating parameters will be effected by the environment they operate in. If the cavities are used in a controlled temperature room, you probably will never have to mess with them. If the operational area is at outdoor temps and humidity, the cavities might have to be tweaked a couple of times a year.

The first question to ask is why does anyone think the cavities need the tender touch of a master technician to wave his hand over them? Is it causing coverage problems for users and your hearing static? Is it just someone trying to make a name and wants to try tweaking the cavities just for no reason?

Repeaters come in many flavors. But the bottom line is they either have good coverage or don't. You can't just stand up and say the duplexer is causing the problem. It could be that the system has taken a lightning strike and damage was done to some part of the system. The antenna could be at fault. You could have water in a coax connector. You could have a loose coax connector anywhere in the antenna system. The receiver could have an issue. The transmitter could be generating a birdie that is causing the receiver not to hear as good as it use to. The last issue is you might even have an intermod problem that could take months to find.

The question to ask is what is the problem? Define the issue and why anyone thinks the repeater is not working correctly. Is there even a problem with the repeater? It could be that someone's radio has lost receiver sensitivity or their transmitter is not putting out like it use to. This could cause them to think that the repeater is not working like it use to.

So far you have not provided any reason to go play with the repeater. Come back with some real word reasons why the cavities should even be thought about being touched. Give the group here reason to think about what steps should be taken. In the mean time, keep the door locked to limit access to the repeater.
 

n0wjh

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repeater duplexers reply

Jim
please read my reply .i belive that you answered between messages .
yes the repeater radio wasnt hearing it does transmit ...the promblem was not hearing well until the last probably lighting strike ???? degrading over time (i think we have 2 promblems one the radio itself which has been send for repair to the factory 2nd the antenna proably phazing lines??? it is a
db224 which i understand is is prone to water damage ??
ever rebuild one of these phazing lines how would you rate the job ???
no NEVER AGAIN TO easy i have the measurements blueprints ect
(it will have a new polyphazer inline when placed back in service and ground rod ect )(and yes it does now X brand never no one has ever heard of )
the duplexers are waco i have the part number but not in front of me
thank you for your help terry N0WJH
 

KC8ESL

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The thing is, a lot of people are beginning to own these Rigol RSA-815 SpecAn's. This tool would be great for the job of TROUBLESHOOTING your issues if you're not experienced. Be careful, you may learn something too.

What are your issues? Receiver de-sense? Is your TX output power attenuated?

It will not hurt anything turn off the repeater and hook up a SpecAn/TG to the duplexer if available and save the club hundreds of dollars on a tech to come out on-site and diagnose for you. My personal recommendation is that unless you have any prior practice in tuning cavity filters, just leave it alone and record your data. They're a tricky bunch to figure out especially with the lack of manuals on the net.

Having said that, I'd also recommend checking out all of your coaxial cables (with the SpecAn/TG, of course) and checking the coaxial connection to the antenna if possible for corrosion.

https://www.arrl.org/files/file/QEX_Next_Issue/Sep-Oct_2009/QEX_Sep-Oct_09_Feature.pdf possibly the best article I've seen on duplexer design/tuning. YMMV.
 

AK9R

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Guys, I'm sure N0WJH appreciates your replies.

However, N0WJH is a new user in these forums and his posts are moderated until he hits the magic number of posts that will automatically lift his moderation. That means that a moderator, such as me, has to come along and approve his posts. Contrary to popular belief, the moderators here do have lives outside RR and don't live in the forums. That means that there may be some lag between the time N0WJH posts in this, or any thread, and the time you can see his messages.

So, take it slow before you jump in with a comment or questions. Give N0WJH some time to reply and give the moderators some time to approve his posts.
 
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Don't touch them until you've swept them with a quality analyzer. If they are good, you've saved 2 hours of twisting knobs and frustration.

If the guy is one of those who has to constantly tinker, get him off of the repeater team or find him something else to tinker with.

Been there, seen that. Welcome to the forums!
 

n0wjh

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further info

ok here is promblem repeater over several years got harder and harder to hear finally quit hearing altogether the radio transcevier it did transmit however is being repaired
by the maker .....
ok the antenna is on a commerical tower at a radio station at 400 feet it is db224 fed with very large commercial hardline what type i dont know ..checked by the radio station engineer and is good
the duplexers are waco there fittings have been cleaned with dexiot ONE CAREFULLY connection at a time and carefully retighten after drying . ..the feedlines to and the radio and from the radio antenna have been tested with a ohm meter for opens and and shorts
the only promblem we found was one feedline the braid wasnt soldered on the pl connector it was clean and bright it has been replaced .......
the antenna itself doesnt hear either please refer to earlier posts or email me terryn0wjh@hotmail.com
i would like to thank everyone who has tryed to help this has been going a long time the club is suffering because of it the ARES group is out a repeater ect ect
we thank the people who preview my posts ...i am not trying to bash anyone myself and one other guy have just started on this problem trying as best as we can fix these promblems PLEASE DONT POST UNLESS YOU HAVE READ THE PRIOR POSTS ...previewers thank you and oneS that are helping thank you terry N0WJH
 

mikewazowski

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You need to get a tech in there with proper test equipment and knowledge of how the whole system works.

He should be able to sweep the antenna system, check the tuning of the duplexer using proper equipment, check the power level out of the repeater, check the insertion loss of the duplexer, conduct noise floor measurements and check the sensitivity of the receiver. I'm sure I've forgotten something but as you can see, checking a repeater for proper operation takes a lot of specialized equipment and knowledge.
 

WA0CBW

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Did I correctly hear you say that you put a handheld on the repeater antenna and you couldn't even hear a WX transmitter but could hear the WX transmitter even with out the antenna connected? That would indicate a severe problem in the coax to the antenna, or the antenna or antenna phasing network itself.
BB
 

nd5y

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Did I correctly hear you say that you put a handheld on the repeater antenna and you couldn't even hear a WX transmitter but could hear the WX transmitter even with out the antenna connected? That would indicate a severe problem in the coax to the antenna, or the antenna or antenna phasing network itself.
BB
It depends on what kind of hand held they used. Some have crappy receivers. Put one on an antenna at 400' on a commercial tower with a lot of other trasnmitters and I would not be surprised if you couldn't hear anything.
 

kayn1n32008

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about 10 years in service ...well we didnt have any other way to test the duplexers onsite so we disconnected the repeater radio and used a handheld to replace the repeater radio it as a simple test

the repeater probably had a surge that took out front end of the receiver and we needed a simple test also damaged the phazing lines on the db224 antenna ....

the coax HARDLINE was checked by the radio station engineer and is good

the antenna is up 400 on a commercial tower so it isnt easy to get to last climber said that it was pitted from lighting strikes can we assume perhaps the phazing lines need to be replaced

also .....

again lacking any other way to test the antenna we used the handheld to test it would transmit and was hearable about 10 miles away it WOULDNT HEAR ANYTHING not even the weather service broadcast that was hearable without the rubber duck antenna ........( handheld --adapter --to coax-- to -hardline -to db224

is this a viable test ????

we couldnt think of anything else easy to do

the repeater has been slowly been degrading until the last perhaps lighting strike ???

that took out the front end ....any ideas we are really struggling with this this repeater has been down down for a about a year causing many problems and endless unfruitful discussions at the club meetings

thank you in advance terry N0WJH

'


Where to start...

Have the duplexer swept using a service monitor and a tracking generator.

Have the feed line Checked out using something like an Anritsu. Look at both return loss, and distance to fault. These tests will show what state both the antenna and feed line are in.

Question: why is the repeater going back to the factory? What brand and model is the repeater?

If the DB224 has a known issue with water, replace the antenna with one that will stand up to the elements and skip building a new phasing harness this will reduce the risk of further problems down the road.

If the phasing harness is toast, Replace the antenna with something like:

From Comprod:

http://www.comprodcom.com/Products/...f-exposed-dipoles-aviation-118-138-mhz_16__5/

Or from Sinclair Radio Labs:

http://www.sinclairtechnologies.com/catalog/product.aspx?id=42


Either of these antennas are FAR more likely to survive water/elements simply due to having the phasing harness NOT exposed and taped to the mast. Heck, if water is an issue, put a rain cap on the antenna mast.



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prcguy

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I can't imagine a DB224 having a problem with the phasing harness, they are very well sealed and the coax is internally flooded with a silicone grease. You don't need an expensive analyzer to rule out coax problems, you can measure power at the radio end of the feedline then again at the antenna and compare the loss to factory spec.
prcguy

Where to start...

Have the duplexer swept using a service monitor and a tracking generator.

Have the feed line Checked out using something like an Anritsu. Look at both return loss, and distance to fault. These tests will show what state both the antenna and feed line are in.

Question: why is the repeater going back to the factory? What brand and model is the repeater?

If the DB224 has a known issue with water, replace the antenna with one that will stand up to the elements and skip building a new phasing harness this will reduce the risk of further problems down the road.

If the phasing harness is toast, Replace the antenna with something like:

From Comprod:

Antennas - 870 Series VHF Exposed Dipoles Aviation (118-138 MHz) | Exposed Dipole Antennas | COMPROD Communication

Or from Sinclair Radio Labs:

Sinclair Technologies Online Product Catalog - SD214-SF2P4SNM(D00)


Either of these antennas are FAR more likely to survive water/elements simply due to having the phasing harness NOT exposed and taped to the mast. Heck, if water is an issue, put a rain cap on the antenna mast.



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n5npo

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Jul 1, 2014
Messages
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I want my 20 yr old DB 224 back.

I can't imagine a DB224 having a problem with the phasing harness, they are very well sealed and the coax is internally flooded with a silicone grease. You don't need an expensive analyzer to rule out coax problems, you can measure power at the radio end of the feedline then again at the antenna and compare the loss to factory spec.
prcguy
Hi,

I have seen many DB-224's with water in the harness. It gets into the molded "Y" junctions, then into the center conductor that is stranded and then on down the harness it goes... I happens mostly to the newer ones made in Mexico. We get a lot of rain in my neck of the wood, so we have quit using the DB antenna and have gone to Comprod or Sinclair. So far, so good.
The water does not get in or go through the silicone grease flooded part. It gets in where the molded plastic at the "Y"s contacts the outer jacket of the VB coax. It then goes into where the center conductors are soldered together and gets into the stranded center conductor which acts pretty much like a wick and down the harness it goes, ofter all the way down into the connector where it connects to the main feed. Then it will fill up the connector with water. I had to completely dissect a harness to get this info. I took photos and contacted Commscope (Andrew/DBProducts). I ended up corresponding with a Mark Situ. He asked me to e-mail me the photos and if I wanted a new harness. I said sure. I had to ship him the old harness, but I got a new one in it's place. The new harness has some changes, but they still leak. I took the new harness, used Scotch C130 (or is that 130C) on all the molded junctions, I then put scotchcote over that to further seal the molded junctions... So far it has not leaked that I can tell. The antenna has been performing well.
My problem is this, sure Comscope will give you a new harness, after you pay a tower crew to take down your antenna, remove the bad harness, box it up and ship it to them. They wont pay the tower crew to re-install the antenna after you replaced and sealed the new harness that you had to exchange.
Best to just put up a more expensive Comprod or Telewave or Sinclair to start with and save the headache a year or two down the road when the DB-224 has to come back down...
73 es good luck.

Norm
 

kayn1n32008

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Hi,



.

My problem is this, sure Comscope will give you a new harness, after you pay a tower crew to take down your antenna, remove the bad harness, box it up and ship it to them. They wont pay the tower crew to re-install the antenna after you replaced and sealed the new harness that you had to exchange.

Best to just put up a more expensive Comprod or Telewave or Sinclair to start with and save the headache a year or two down the road when the DB-224 has to come back down...

73 es good luck.



Norm

You get what you pay for.

I am a member of 2 different clubs, and both clubs have V/UHF repeaters that, some of them, are on 20+ year old Sinclair antennas, that are still going strong. Why mess with cheap antennas that are going to cause problems down the road? Better off to spend the $1600+ on an antenna that will survive, than a $500 one that you will have to replace, considering a good rigging crew will probably be $5000+ to climb a tower twice.


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