Duplexer insert keeps burning out.

[triode]

Hello everyone, Please advice.  

I am on my third duplexer now I keep on burning Teflon inserts on transmitter side. It works for a week or so then gradually I am hearing popping sounds and distance drops. Checking duplexer with SV4401A and it is completely out of tune both HIGH and LOW sides effected. I am using KG-1000G plus and it outputs approximately 38-45(fluctuating) watt. 

My question is. What do I do besides reducing transmitter power and does anyone know where I can purchase the insert replacements or maybe there is a DIY solution for this. 

BTW. I tried to replace it with Teflon tube from 3D printer filament line. After tuning it lasted about 3 minutes with 50ohm load (burned). again, this happens to 3 duplexers.

Thank You. 

 

[Lscott]

Just a wild thought. What is the power and duty cycle rating of the duplexer?

[triode]

SGQ-450A-D 50watt, duty cycle I am not sure but I am assuming duplexer should run continuously. I don't recall seeing duty cycle on the duplexer parameters list. 

[Flameout]

I had that happen once on a cheap Chinese Fumei duplexer. Not sure what or why it happened. I just ended up buying a used 633-6A-2N on ebay and it's been fine ever since

[triode]

Getting something like 633-6A-2N maybe a solution but I really want to fix those duplexers I already burn because they worked well when they did.  

 

[Lscott]

5 hours ago, triode said:

SGQ-450A-D 50watt, duty cycle I am not sure but I am assuming duplexer should run continuously. I don't recall seeing duty cycle on the duplexer parameters list. 

I wouldn’t assume a 100% duty cycle. Those cheap Chinese Duplexers were primarily designed for mobile applications, I believe, which are low duty cycle.

[Lscott]

This is what I have on file for one of those cheap Chinese Duplexers.

SGQ-450D-N.pdf Chinese Mobile Duplexer Measurements.pdf

[Flameout]

3 hours ago, triode said:

Getting something like 633-6A-2N maybe a solution but I really want to fix those duplexers I already burn because they worked well when they did.  

 

If you have 3 of them now, can't you take the parts from the bad ones to make one good one?

[triode]

Yes, I took all of them a part and move inserts from HIGH side to LOW side and make DIY inserts for HIGH side from 3D printer Teflon filament guide cable. 

 

[gortex2]

Price of 3 you could have bought a real duplexer.....

[Sshannon]

21 hours ago, triode said:

My question is. What do I do besides reducing transmitter power and does anyone know where I can purchase the insert replacements or maybe there is a DIY solution for this. 

My dad used to say “Why did the man keep pounding his head against the wall?  Because it felt so good when he stopped.”  This seems to be a similar situation.

By saying “besides reducing transmitter power” you drastically limit the options. It’s obvious that the duplexer you continue to use cannot withstand operation as you wish.  Your choices are really the following:

1. Reduce the power (you might be surprised how little that affects the range),
2. Buy a better duplexer,
3. Contact the customer service department for the duplexer you continue to use and subscribe to the “insert of the month/week/whatever club”,
4. Consult with a technical ceramics company to see if they can make you some custom ceramic inserts.  They would withstand the heat, but eventually the heat might affect a nearby portion of the duplexer, shifting the failure elsewhere.  Yes, that would cost some money, but so does repeatedly buying a duplexer that doesn’t operate at the level at which you have chosen to operate.

It’s obvious (thricely reinforced) that the duplexer in question simply isn’t designed for what you’re trying to do at the power output you insist on using, even if the manual or specifications differ.  Saying “but it works so well while it works” simply doesn’t make good sense except as a temporary installation while researching a permanent solution.

Regarding choice #3 above, if you cannot contact customer service for the duplexer you like, that’s another reason to switch.

I wish you well in your quixotic quest. Please do let us know what you eventually decide to do.

[gortex2]

My question is how is this happening. On GMRS the duty cycle should not be enough to melt it down. This is analog correct ? How long are you keyed for to do this damage ? 

[Sshannon]

19 minutes ago, gortex2 said:

My question is how is this happening. On GMRS the duty cycle should not be enough to melt it down. This is analog correct ? How long are you keyed for to do this damage ? 

That’s a good point.  Maybe the issue isn’t the RF power, but something else, such as static discharge or a ground loop current.

[triode]

Yes and No, I could buy one good duplexer for price for 3 but I purchased them over period time and as I worked through problems I gain experience in building repeaters, tuning antennas, duplexers, troubleshooting, writing code for controllers, making interfaces between radios and cliché statements about "banging head in to the wall" does not really answering my question, but thank you for your input. 

Money can solve many problems but, in my opinion, it is most primitive, boring solution, and at the end with no satisfaction/reward but emptiness, please if this is all you can say "spend more money" do not use your valuable time writing it. 

Nothing is permanent, maybe(most likely) I would end up spending more money but hobby for me is not having working solutions but the process itself of making it work.

Also I am not looking for opinion please post your real solution if you have it, If not maybe I will post mine if I solve it. I am sure someone will benefit from making work so called cheap duplexer.

 

Thank You all for your time and advice. 

 

[triode]

According my understanding everything is grounded including myself (lol). The only doubts I have about jumper cables I use 1/2 weave length and approaching 50ohms at both ends for transmitter and receiver. I am using rg174 and 25ft cable to LMR400 cable to antenna. Yes is analog. Again inserts are getting burned randomly there is no specific duration. One of the duplexers from XLT Communications burned immediately and it is most expensive one I have. 

[Sshannon]

30 minutes ago, triode said:

Yes and No, I could buy one good duplexer for price for 3 but I purchased them over period time and as I worked through problems I gain experience in building repeaters, tuning antennas, duplexers, troubleshooting, writing code for controllers, making interfaces between radios and cliché statements about "banging head in to the wall" does not really answering my question, but thank you for your input. 

Absolutely none of the educational experience you gained was as a result of burning out a piece of Teflon.  Burning out the insert was a distraction, taking you away from all those other things which are interesting.

Solving a problem by spending money might be boring, but doing the same thing three times and getting the same results isn’t any better.  You’ve encountered a technical limitation of some kind and rather than trying reducing power, you did exactly the same thing with exactly the same results.

You did try a 3D printed replacement, which would be a low temperature replacement, and it failed immediately, so the next thing to try would be a material that’s unaffected by heat.  Buy a phenolic or Bakelite rod and have some inserts machined at a local machine shop.  

Also, reduce power, even if only temporarily.  The assumption is that this problem is power related. If you halve your output power and the failures are repeated, then it might not actually be your power output.

[Radioguy7268]

Those compact "flat pack" duplexers are not really designed for 50 watt applications. I also didn't quite catch who was tuning those duplexers. I've seen some sold on Ebay that are horribly tuned, and others that have been tuned quite well. I would not blindly trust that a CCD (CheapChineseDuplexer?) is actually tuned to the frequencies requested when it was ordered.

I would also tell you that the amount of isolation between transmit and receive doesn't really allow you to run 50 watts through one of those flat packs (even when it's properly tuned) without some level of desense. In short - a portion of your transmit signal is going to leak over to the receive side and cause you interference - AKA desense, reducing the performance of your own repeater.

And finally - the point I always get back to.  Every rookie out there wants to get a full 50 watts, because more power is always more better - right?  Well, think about what you're doing. You may get a full 50 watts heading into your duplexer, and if you're lucky, 30 or 35 watts heading out of the duplexer & up to your high gain antenna.  But, what are you talking to? Hand held portables at 4 or 5 watts? How far can they talk back in?  You just reduced their talk-back performance by leaking some transmit power over to the receive side, probably killing 2 or 3 dB of receiver sensitivity. Now that 4 watt portable is effectively talking in with the same effectiveness as a 2 watt portable, because you're reducing the receive side performance all so you can crank 50 watts into the duplexer.  Back the power down to 20 watts, still have ERP to spare, and suddenly your 4 watt portable gets back into the system a bunch better, repeater coverage is balanced between transmit and receive, and as an added bonus, parts live longer due to reduced power.

Turn down the power. Improve your system performance.

[gortex2]

Again I guess I'm more confused now. Is this an N connector on the duplexer ? Looking at your picture I'm not sure where that part would go. On all my flat pack duplexers they are N. There is no insulator in there center. Can you show us a picture of where this is ? 

@Radioguy7268 is correct. No matter what you jam in your loosing power thru the duplexer. Back it down to 25 and be good. I have used the flatpack ones in the past for small repeaters and never seen the issue you are describing with a proper N connector and quality cables. 

[triode]

Again doing the same thing 3 times or more and expecting different results does not really apply here. When Teflon burns and you don't know it yet, you hear all kinds sounds audio is getting bad while transmitting I had to look at controller making sure there is no problems with circuitry I have made. Power supplies, fan filters, antennas and only then started looking at the duplexers because it does not always immediately going bad it retains tuning for a while when testing with VNA even with burned Teflon. So Teflon is the source of experience (lol) 

Yes I have noticed reducing power in half like to 20 watts does helping the leak to receiver side with little impact on transmitting distance. But again this is work around, if I agree with it then I will stop looking for solution. 

[triode]

Posting the image of the duplexer for gortex2. 

[gortex2]

OK. I have never seen this happen. I can only guess and say its poor quality stuff, or improper tuning. 

[triode]

This would not be a tunning, sellers tuned two, another was send to tuning service, later rest of duplexers I tunned myself. Some served longer than others but then 

burned inside. I am surprised there is no information on this issue. I am using KG-1000G plus on transmitter side, maybe radios is the problem.

Thank you for responding. 

[K7lon]

I have had this same duplexer for several years. Its on a 440 5 watt portable reapter with no issues. It was good to be able to see inside the back, and wierd only one tip is burning. It does appear that it's listed rating exceeds it's actual capabilities. My only complaint would be the 3 db insertion loss. So I have switched to Celwave for GMRS and have a .8 to 1.3 db loss, and they tune up lot easier for this rookie. Effective range seems marginally better too (15%).

This is just an off the wall idea for a  repair. Create a simple silicone mold and use a casting epoxy then drill out the center on a  drill press. Casting epoxy can withstand a lot of heat. This could be a huge success or just another lesson on life's journey.

I hope the idea helps,  good luck with hobby.

WRJA397 

[triode]

Actually this is good practical advice, I was planning to use fiberglass raisin and Plaster of Paris mixed. But the way I solve it (at least it is working for a more than a month now and it is not burning) is by replacing the tuning screws with brass crews and turn them on the lathe removing threads making ends cone-shaped approximately 30 degrees and 3mm cone, thinking that cone-shape is better than uneven threads area and creates some air gap between Teflon and screws. I also took insert from receiving side and switch them to transmitting side and put DIY inserts made from 3d printer filament guide into receiving side. Then I tune duplexer with VNA(SV4401A) as best as I could and fine tune it by the sound(listening on the radio) decreasing attenuation of RF signal (coming from tinySA) for better rejection as I tune. Again is this a good solution, probably not but it works for now. Next time around I will cut the tuning tubes and solder the wider copper or brass tubes on top of it, then will turn Teflon inserts on the lathe for wider diameter of new tubes, also silver plate tubes and screws after tuning them on the lathe. 

 

Thank you so much for taking your time to respond.