Duplexer

[JamesBrox]

My OCD kicked in on this GMRS repeater project. Is MY labeling correct on this duplexer?

Thx WRXU693

[Radioguy7268]

If you are talking to 4 watt portables - who cares how much power gets through the duplexer? A "tight" duplexer tuning that loses more dB is preferable to a sloppy duplexer tune job that gets more power/less dB loss.

Remember, you are using the duplexer to achieve isolation between the transmit and receive frequencies. Isolation is your key measurement - NOT power throughput.

On most of these rigs built with an inexpensive notch AKA compact duplexer and 2 mobile radios, turning DOWN the transmit power will result in better overall range, less desense, and longer equipment life. 

 

 

[WRKC935]

If your SWR is 3-1 that's a big part of it. 

Duplexers are tuned circuits that require a proper impedance at all points connected to it for it to work right.  A 3 to 1 SWR is NOT a 50 ohm impedance.  And it WILL screw with the functioning of the duplexer a lot. 

The KG1000 radios are not an ideal repeater setup to be sure.... but having that sort of mismatch on the antenna is certainly going to have an effect.

When you tune a duplexer, you connect the VNA / spectrum analyzer to two ports of the duplexer.  One port is obviously the antenna port and the other port is the side being adjusted.  You then connect a 50 ohm load to the other port so the duplexer has a proper 50 ohm impedance on all ports.  You can see the change in tuning when you connect the load if the monitor is already connected.  I have never tried connecting a 75 or 100 ohm load to the port simply because there was never a situation that called for it. 

 

Without a proper service monitor with Duplex functionality, it would be hard to measure the desense caused by the mismatch, but I would certainly expect to see it.

 

[JamesBrox]

19 hours ago, Sshannon said:

So if nothing else changed but the location of the SW102, I’m guessing the two watts difference is just a problem with the sw102, because it is simply not possible for a duplexer to add power. But the real point is that it looks like the most significant losses are happening in your cable, not your duplexer. 
Your duplexer claims a loss of 1.5 dB. That’s 25% of whatever goes into it, which is probably not unreasonable. If you have 18 watts entering the duplexer you should have roughly 13-14 watts coming out. 

How long is the cable between your transmitter and the duplexer and what kind of cable is it? That can help us estimate what the losses should be there. Your readings indicate that you lost 30 watts out of 48 watts. That’s 62.5%, or 5/8 of your power, which is 4.25 dB loss.

How long is the cable between your duplexer and the antenna? You already said it is LMR400. Is is genuine Times-Microwave LMR400 or one of the many copies?

 

Hey Shannon, Thank you the follow up questions and trying to figure out what's going on here. But I'm going back to having a base station with one radio and a mobile radio in the truck. I got more enjoyment out of that. Maybe someone will built a gmrs repeater in my area who has the knowledge and know-how for such. Thanks again

WRXU693 

[SteveShannon]

6 minutes ago, JamesBrox said:

Hey Shannon, Thank you the follow up questions and trying to figure out what's going on here. But I'm going back to having a base station with one radio and a mobile radio in the truck. I got more enjoyment out of that. Maybe someone will built a gmrs repeater in my area who has the knowledge and know-how for such. Thanks again

WRXU693 

I hope nothing I said made you change your mind.

[JamesBrox]

15 minutes ago, Sshannon said:

I hope nothing I said made you change your mind.

No bud. It's just too difficult with way too many variables without having someone that can physically look at what's going on and unfortunately gmrs hasn't caught on yet in my county. 

[gortex2]

sounds like you need quality cables from radio to duplexer. Shouldn't be long at all. 

[JamesBrox]

4 minutes ago, gortex2 said:

sounds like you need quality cables from radio to duplexer. Shouldn't be long at all. 

No, they weren't long, just long enough to reach the duplexer...nothing excessive. Yeah the cables are made in China "Superbat" brand.... but what isn't these days  

[OffRoaderX]

12 minutes ago, JamesBrox said:

the cables are made in China... but what isn't these days  

My cable.

[JamesBrox]

12 minutes ago, OffRoaderX said:

My cable.

Well, good to know the jumpers weren't the issue. 

[SteveShannon]

Although you told us the brand, you didn’t really say what the actual length and type of the cable, such as KMR400.  

I really like M&P cables which are made in Italy and ABR cables which are made in the USA and Times-Microwave by MPD which are also made in the USA. 

[JamesBrox]

1 hour ago, JamesBrox said:

No, they weren't long, just long enough to reach the duplexer...nothing excessive. Yeah the cables are made in China "Superbat" brand.... but what isn't these days  

 

1 hour ago, gortex2 said:

sounds like you need quality cables from radio to duplexer. Shouldn't be long at all. 

Any other recommendations besides buying a "cheap" $1800 duplexer?

[JamesBrox]

5 minutes ago, Sshannon said:

Although you told us the brand, you didn’t really say what the actual length and type of the cable, such as KMR400.  

I really like M&P cables which are made in Italy and ABR cables which are made in the USA and Times-Microwave by MPD which are also made in the USA. 

They are 2' jumpers. RG-58A/U

 

[SteveShannon]

1 minute ago, JamesBrox said:

They are 2' jumpers.

 

None of the measurements you have provided indicate a problem with the duplexer, but they do indicate extremely high losses in the cables, especially for that length. 

[JamesBrox]

3 minutes ago, Sshannon said:

None of the measurements you have provided indicate a problem with the duplexer, but they do indicate extremely high losses in the cables, especially for that length. 

That length? 24"? Too close? Or does that matter?

[WRXB215]

4 minutes ago, Sshannon said:

they do indicate extremely high losses in the cables

Possibly the connectors?

[SteveShannon]

2 minutes ago, JamesBrox said:

That length? 24"? Too close?

No, possibly just a bad cable. 
You have 48 watts coming out of the radio. Two feet later you should still see 48 watts, unless it’s a type (what type is it?) that has super high attenuation. 

[JamesBrox]

Just now, WRXB215 said:

Possibly the connectors?

Well, I've posted SWR readings from 3 out of 4 recommended connections points. I don't know what else I can say. 

[SteveShannon]

1 minute ago, WRXB215 said:

Possibly the connectors?

Could be. Could also be the cable construction or too tight of a bend. But losing 30 watts in two feet is an extremely high loss. I would go buy a piece of real LMR400 with good connectors already installed at the very least. 

[JamesBrox]

3 minutes ago, Sshannon said:

No, possibly just a bad cable. 
You have 48 watts coming out of the radio. Two feet later you should still see 48 watts, unless it’s a type (what type is it?) that has super high attenuation. 

Brother. I appreciate it. But I've already gave the manufactures origin. Brand name, Length and type of cable.....

[JamesBrox]

7 minutes ago, Sshannon said:

Could be. Could also be the cable construction or too tight of a bend. But losing 30 watts in two feet is an extremely high loss. I would go buy a piece of real LMR400 with good connectors already installed at the very least. 

There are 90 degree manufactured connectors on these cables to help the flow of wire to the duplexer. Who uses LMR400 as jumpers?

[SteveShannon]

I’m going to go work on my cabin. I’ll check in later.  I wouldn’t get too hung up on SWR until you have the cable losses figured out. A dummy load has a perfect SWR. Super lossy system will also result in a very low SWR because the reflected power is so low. So SWR in this case is meaningless.  Power measurements at each transition is the real test. 

[SteveShannon]

2 minutes ago, JamesBrox said:

There are 90 degree manufactured connectors on these cables to help the flow of wire to the duplexer. Who uses LMR400 as jumpers?

Me

[SteveShannon]

Watch this to see the problem with 90° connectors (except silver plated amphenol ones).

 

[JamesBrox]

5 minutes ago, Sshannon said:

Me

Send me a link where I can buy these LMR400 two foot cables. Thx

[SteveShannon]

https://www.polyphaser.com/2-ft-uhf-to-uhf-m-m-400-series-low-loss-cable-jumper?creative=&keyword=&matchtype=&network=x&device=m&gad=1&gbraid=0AAAAADuUXEAGe1sTFWw7lLUNDWSUXIcEz&gclid=Cj0KCQjwhL6pBhDjARIsAGx8D595HSFQtqWtHdumnNhUeir3UBZn6TIUWo0dQy9Ai3Wpm9FzVL1A7ocaAkCVEALw_wcB