Duplexer

[JamesBrox]

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

Thx WRXU693

[Sshannon]

53 minutes ago, JamesBrox said:

I'm asking you. I see your name pop up all the time, no matter what the topic. With you being a ham on a gmrs forum....what makes his system work so well? 

Good equipment, good planning, and Kenny has experience and understands the basics. He chose a good repeater, duplexer, and antenna. He used good quality coax. He used Amphenol connectors and he even tried to use all N connectors instead of PL259/SO239 connectors. 
 

[gortex2]

yes

[JamesBrox]

8 hours ago, gortex2 said:

yes

Thanks. I'm doing some testing with an HT about 1/4 mile down the road, clear line of sight. The repeater has the travel tone PL RX/TX and the HT has the same PL. Yet I don't hear the "kerchunk" on the HT. Any ideas? 

 

[Sshannon]

23 minutes ago, JamesBrox said:

Thanks. I'm doing some testing with an HT about 1/4 mile down the road, clear line of sight. The repeater has the travel tone PL RX/TX and the HT has the same PL. Yet I don't hear the "kerchunk" on the HT. Any ideas? 

 

Not all repeaters will continue to transmit after you briefly press the PTT button. It’s better to get on and ask someone for a radio check. 

[nokones]

What are you using for a repeater station? Just curious.

[JamesBrox]

2 hours ago, nokones said:

What are you using for a repeater station? Just curious.

Using 2 KG-1000G+'s. The very good video set up from BTWR is focused on the 1000G. But the 1000G+ is a little different. 

[nokones]

FYI - I found horrendous amount of desense between two KG1000G Plus radios that were side-by-side. With a Motorola XTS5000 portable radio transmitting 3.7 watts, I only got .7 mile from the repeater on flat terrain, in otherwords just straight down the street before any turns until the mobile could no longer be received by the receiving radio when the transmitting radio was keyed. The TX out was no problem in being received by the mobile or portable radios. With a 50 watt mobile measured with 44 watt of RF output with a 2.4 dB omni mobile antenna with a VSWR of 1.2:1, I got about 1.8 miles.

At first, I thought my problem may have been the duplexer or a cable or two but everything swept out good. I stopped the duplex function and I ran a test transmitting through the duplexer and the same antenna with one of radios in the simplex mode, and received on the other radio with a separate antenna and drove around using a portable and had great results and farz throughout the area of at least 5 miles away.

I reversed the testing procedure of receiving through the duplexer and using the same antenna connected to the duplexer and still had great results as before. That procedure essentially eliminated the duplexer and cables as being the problem. However, I took the duplexer back to EMR Corp to have them recheck it and it was performing as designed and tuned.

I reconnected the duplexer and ran my test again and still no farz with the two radios acting as a repeater. 

I called a friend and asked him to bring over his two Maxon radios configured as a repeater and ran my same test and used the same TX points and we got many farz. This test results proved there must be a desense problem probably due to poor shielding between the two radios. The function of the two radios were also reversed and that did not change the results.

So, I learned my lesson in trying to go cheap. I decided to buy a real repeater station and installed it. On flat terrain, I got about 10-12 Miles with a portable and about 22-25 miles with a mobile radio. And my duplexer is still working great and has not burned out the plastic inserts like the cheap duplexers are doing.

I called the selling Dealer, because the two radios were still under warranty, explaining the problem that I was experiencing and my testing procedure. The Dealer's Tech Support person essentially questioned my testing procedure stated that my testing procedure was not technical and scientific enough for me to arrive at my conclusion. I told him that I am not an engineer but it still was a real world in the environment testing with poor results from the two radios acting in tandem as a repeater unit and fine as separate simplex stations.

Well his candor really gave me a warm and fuzzy feeling that I was in a favorable position so I just requested a refund. He stated that I need to ship everything back so they can conduct their own test in order to get a refund.

Fortunately, I was able to sell one of the radios and for some stupid reason thought it would be a good idea to keep one of them for another base station. That was kinda of a mistake, oh well. Never again.

I sold one of the radios to a Club member and kept one as a second Base radio mostly for monitoring two other nearby repeaters.

[Sshannon]

Notarubicon, Randy, @OffRoaderX had similar problems with desense when he tried to build a repeater using two KG1000 transceivers.  He switched to a purpose built repeater also.

[JamesBrox]

Here's the specs.

[Sshannon]

31 minutes ago, JamesBrox said:

Here's the specs.

The duplexer wasn’t the cause of the desense. Poor shielding on the radios appeared to have been.

[OffRoaderX]

As @Sshannon said I too experienced desense with my KG1000 repeater build, but after separating the radios and adding some shielding i was getting 15+ miles of farz.  But switching to a VXR7000 repeater more than doubled my farz even though it outputs about half the power.

[WRQC299]

As [mention=6309]Sshannon[/mention] said I too experienced desense with my KG1000 repeater build, but after separating the radios and adding some shielding i was getting 15+ miles of farz.  But switching to a VXR7000 repeater more than doubled my farz even though it outputs about half the power.

VXR7000- Are those discontinued? Just pick one up second hand, I suppose.


Sent from my iPhone using Tapatalk

[OffRoaderX]

Just now, WRQC299 said:

VXR7000- Are those discontinued?

Yes.. I got a very gently used one for $500.  

[JamesBrox]

Well, my son is home today and I'm on vacation so that gave me the opportunity to do a field test. Him in the shack and me on a HT down the road. Good news is that the repeater set up seems to be working but the bad news the duplexer robbed most of the watts from the radio (50w) and the SWR is not ideal. 

[Sshannon]

11 minutes ago, JamesBrox said:

Well, my son is home today and I'm on vacation so that gave me the opportunity to do a field test. Him in the shack and me on a HT down the road. Good news is that the repeater set up seems to be working but the bad news the duplexer robbed most of the watts from the radio (50w) and the SWR is not ideal. 

Based on the specs you showed above for insertion loss, the duplexer alone shouldn’t take away that much power.  How and where are you measuring power?  If you don’t have one, I would recommend getting a power meter and putting it inline at different points between the radio and antenna to see what the actual power level is at that point. I would put it:

Right at the antenna connector on the TX radio.

At the end of the TX cable where it connects to the duplexer.

At the duplexer antenna output before the cable.

At the antenna end of the coax.

You can measure SWR at each place.

Obviously all measurements must be while transmitting.

 

[WRXB215]

1 hour ago, WRQC299 said:

Are those discontinued?

https://www.buytwowayradios.com/vertex-vxr-7000.html

[JamesBrox]

8 minutes ago, Sshannon said:

Based on the specs you showed above for insertion loss, the duplexer alone shouldn’t take away that much power.  How and where are you measuring power?  If you don’t have one, I would recommend getting a power meter and putting it inline at different points between the radio and antenna to see what the actual power level is at that point. I would put it:

Right at the antenna connector on the TX radio.

At the end of the TX cable where it connects to the duplexer.

At the duplexer antenna output before the cable.

At the antenna end of the coax.

You can measure SWR at each place.

Obviously all measurements must be while transmitting.

 

With a Surecom SW-102. Between the antenna and the duplexer. Yes, measurements obtained while transmitting.

[JamesBrox]

Radio to Surecom to dummy load. SWR 1.1 Watts 48

Radio to duplexer to  Surecom to dummy load. SWR 1.0 Watts 18

Radio to duplexer to Surecom to LMR400 to Ed Fong antenna. SWR 3.0 (sucks) / Watts 20

[Sshannon]

35 minutes ago, JamesBrox said:

Radio to Surecom to dummy load. SWR 1.1 Watts 48

Radio to duplexer to  Surecom to dummy load. SWR 1.0 Watts 18

Radio to deplexer to Surecom to LMR400 to Ed Fong antenna. SWR 3.0 (sucks) / Watts 20

Thanks! That’s helpful, but it still doesn’t tell the effect of coax cable losses.  I assume your first reading is right at the radio end and appears reasonable.

Your second reading shows the sum of the losses between the radio and the duplexer output, but doesn’t isolate the losses in the cable leading to the duplexer.  Or maybe you didn’t have a long cable in the path. Maybe you were just using short jumpers?

Anyway, it’s obvious you’re losing nearly 60% before it ever gets to the antenna

[JamesBrox]

10 minutes ago, Sshannon said:

Thanks! That’s helpful, but it still doesn’t tell the effect of coax cable losses.  I assume your first reading is right at the radio end and appears reasonable.

Your second reading shows the sum of the losses between the radio and the duplexer output, but doesn’t isolate the losses in the cable leading to the duplexer.  Or maybe you didn’t have a long cable in the path. Maybe you were just using short jumpers?

Anyway, it’s obvious you’re losing nearly 60% before it ever gets to the antenna

Yeah, this is just a hobbyist meter. Nothing high end. It's not going to tell me effects of coax cable.

Yes, I'm using short jumper where needed during the testing. So, your diagnoses? 

[Sshannon]

4 minutes ago, JamesBrox said:

Yeah, this just a hobbyist meter. It's not going to tell me effects of coax cable.

Yes, I'm using short jumper where needed during the testing. So, your diagnoses? 

I can’t diagnose it if it’s not really what you’ll be using.

Even though it not an antenna analyzer, by setting everything up just like you would use it, and then inserting the sw102 at each of the four points l list above, you see what the power is at each point and you are able to isolate each element in the system, including each piece of coax.  

[JamesBrox]

 

"see what the power is at each point"... 

Right at the antenna connector on the TX radio. 48w

At the end of the TX cable where it connects to the duplexer. 18w

At the duplexer antenna output before the cable. 20watts

At the antenna end of the coax.  Can't, it's 40' above ground. 

 

"I can’t diagnose it if it’s not really what you’ll be using."

Yes, I'm testing the same equipment, Coax, duplexer and antenna I'll be using.

 

[Sshannon]

34 minutes ago, JamesBrox said:

 

"see what the power is at each point"... 

Right at the antenna connector on the TX radio. 48w

At the end of the TX cable where it connects to the duplexer. 18w

At the duplexer antenna output before the cable. 20watts

At the antenna end of the coax.  Can't, it's 40' above ground. 

 

"I can’t diagnose it if it’s not really what you’ll be using."

Yes, I'm testing the same equipment, Coax, duplexer and antenna I'll be using.

 

So that tells me that you’re losing 30 watts in the coax before it even gets to the duplexer. Then miraculously you get 2 watts back in the duplexer. 🫨

 

[JamesBrox]

1 hour ago, Sshannon said:

So that tells me that you’re losing 30 watts in the coax before it even gets to the duplexer. Then miraculously you get 2 watts back in the duplexer. 🫨

 

that's what it read. 

[Sshannon]

46 minutes ago, JamesBrox said:

that's what it read. 

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?