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Range decreases with Duplexer


WSCV533

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Once again I am in need of some assistance. Everyone was very helpful last time so I have faith.

I am in the process of building my first repeater for family use. I have the antenna approximately 30ft above surface, and get decent range using simplex on my 25 watt radios. My problem starts when I connect the duplexer to my setup. I am able to receive and transmit properly, but my range has decreased from ~15 miles to less than one mile. The SWR through the duplexer tested at 1.8 which is less than ideal but I wouldn't assume that to cause such a drastic loss. So now I leave it to y'all's expertise, I'm sure I'm missing some information. I am using LMR400 cable about 50ft long.

Update: I have disconnected the duplexer and am temporarily running a "parrot" system to test range. As per luck, someone was monitoring my system at that moment. I was able to reach a contact a few miles away and another over 10 miles away using this parrot system. I guess it's time to invest in a new repeater system.

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50 minutes ago, nokones said:

If you are using two Wouxun KG1000G Plus mobile radios and a cheap Chinese POS $150 duplexer that's your problem. Those radios do not have any shielding and you are desensing the receiving radio with the transmitting radio and the duplexer also is contributing to the problem.

Not using those radios but that could definitely be the problem. I was going to try shielding the receiver more as I have them pretty close to each other. Any suggestions as to methods?

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30 minutes ago, WRXP381 said:

What is the wattage after the duplexer.   They do absorb watts but should not be that much.  Maybe it’s it not tuned Correctly? 
what equipment are you using?  

Wattage before duplexer is about 24 watts, after duplexer generally around 18 to 20 watts. Using a Btech 20v2 for receive and a Radioditty db-20G for transmit.

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9 hours ago, WSCV533 said:

Wattage before duplexer is about 24 watts, after duplexer generally around 18 to 20 watts. Using a Btech 20v2 for receive and a Radioditty db-20G for transmit.

Well a a drop from 24-18 shouldnt kill the distance at all.  A 5w hand held will do the 15miles easy.  Something else has to be going on.  Tuning or coax or antenna or a connector or something.  

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Posted (edited)
29 minutes ago, WRXP381 said:

Well a a drop from 24-18 should it kill the distance at all.  A 5w hand held will do the 15miles easy.  Something else has to be going on.  Tuning or coax or antenna or a connector or something.  

That narrows it down lol. Yeah I figured I just had something fubbernucked. Time to hyper analyze the whole system 😅. I was also thinking coax. Quick question, if the SWR is acceptable and power loss is minimal; does that rule out the duplexer? Also, should the radios be further apart? I currently have them only 5 feet apart but there is a metal wall barrier between.

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9 hours ago, WSCV533 said:

Once again I am in need of some assistance. Everyone was very helpful last time so I have faith.

I am in the process of building my first repeater for family use. I have the antenna approximately 30ft above surface, and get decent range using simplex on my 25 watt radios. My problem starts when I connect the duplexer to my setup. I am able to receive and transmit properly, but my range has decreased from ~15 miles to less than one mile. The SWR through the duplexer tested at 1.8 which is less than ideal but I wouldn't assume that to cause such a drastic loss. So now I leave it to y'all's expertise, I'm sure I'm missing some information. I am using LMR400 cable about 50ft long.

Measuring your SWR on the radio side of the duplexer will cause the SWR measurement be lower than it really is. The reason is because SWR is calculated using the forward power and the reflected power, but at the radio you see all of the forward power (because it hasn’t been run through the duplexer yet) and you measure less of the reflected power than actually would happen without the duplexer. Your forward power is attenuated going through the duplexer and then some of it reflects and the reflected power is attenuated again on the way back to the SWR meter so it’s simply a low reading. 
For the best SWR reading, put the SWR meter right at the antenna. 

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SWR really doesn't mean alot for a duplex system other than TX power. You also need to receive on the receive radio and not have decense. What duplexer do you have ? What is the tuned specifications ? You will have a db loss in the duplexer back to your receiver. Depending on the duplexer there could also be decense in that. Lots of variables when you change from a standalone base to a repeater.

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If you are using two Wouxun KG1000G Plus mobile radios and a cheap Chinese POS $150 duplexer that's your problem. Those radios do not have any shielding and you are desensing the receiving radio with the transmitting radio and the duplexer also is contributing to the problem.

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1 hour ago, gortex2 said:

SWR really doesn't mean alot for a duplex system other than TX power. You also need to receive on the receive radio and not have decense. What duplexer do you have ? What is the tuned specifications ? You will have a db loss in the duplexer back to your receiver. Depending on the duplexer there could also be decense in that. Lots of variables when you change from a standalone base to a repeater.

I have a no brand china duplexer. It is rated at 30 watts and marked as tuned for 467.700 and 462.700. yes, Im aware that the quality of the duplexer is not ideal, but others have had better experience. I am attempting to shield the receiving radio to hopefully lessen the desense, any suggestions?

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Unfortunately, based on the wattage mentioned, I don't think the duplexer is doing much, if anything.  A typical 'notch only' 6 cavity duplexer (3 transmit and 3 receive) will experience 3dB or more signal attenuation, cutting your signal in half.  However, when properly tuned, even losing half the signal is still a significant improvement over the desense of using two close proximity antennas with no duplexer at all. 

 

Do you have a VNA available to you?  Or a friend with one?

 

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35 minutes ago, WSCV533 said:

I have a no brand china duplexer. It is rated at 30 watts and marked as tuned for 467.700 and 462.700. yes, Im aware that the quality of the duplexer is not ideal, but others have had better experience. I am attempting to shield the receiving radio to hopefully lessen the desense, any suggestions?

My suggestions besides getting a quality duplexer like a Celwave or EMR Corp. duplexer, is scrap the idea of using two mobile radios that were not designed for a continuous duty cycle and a multi-radio environment and get a real repeater and save your money, time, and energy.

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I have to agree that using a dedicated repeater with a quality duplexer is the way to go. Our club is using a Bridgecom repeater setup for GMRS and we went with a separate duplexer that one of our members tuned using the proper equipment.

Mobile radios just can't handle the high duty cycle like a repeater can. Plus here is the defense issues with having antennas and radios close together. Using a cheap duplexer and cheap/wrong type of coax cable will make the problem worse.

@OffRoaderX tried using two Wouxun KG-1000G radios and he went to a dedicated repeater since he was having issues when using two mobile radios. He can definitely give you insight on this. 

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I'll be taking everyone's suggestions and get a dedicated repeater. Any suggestions are appreciated.

40 minutes ago, WRYZ926 said:

OffRoaderX tried using two Wouxun KG-1000G radios and he went to a dedicated repeater since he was having issues when using two mobile radios.

Yes I watch NotaRubicon on YT, he also mentioned that the Wouxuns worked but he wanted something better. I'm gonna give up on my budget build and splurge on something manufactured for this purpose.

1 hour ago, nokones said:

My suggestions besides getting a quality duplexer like a Celwave or EMR Corp. duplexer, is scrap the idea of using two mobile radios that were not designed for a continuous duty cycle and a multi-radio environment and get a real repeater and save your money, time, and energy.

Probably gonna end up taking your advice. Got any suggestions for a repeater?

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I am going to suggest a Bridgecom repeater if buying brand new. Or look for a used Motorola repeater that can be programed/setup for GMRS. For the best results, you are also going to want to use a separate/external duplexer versus the small duplexers that are built into repeaters. Our club is using Motorola repeaters for 2m and 70cm and a Bridgecom for our GMRS repeater. We use external duplexers on all of our repeaters.

I know there are the portable repeaters from Retevis and Midland, those are fine for temporary use or only covering a small area since they are low power. I would also stay away from the BTech GMRS repeaters until they work all of the bugs out. 

Bridgecom has sales all of the time and their sales prices are lower than what the BTech repeater costs.

A few of us tested the Bridgecom repeater out for about 2 months before opening it up to the public. We put it through its paces and tested the duty cycle. The Bridgecom passed and is working well for us.

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12 hours ago, marcspaz said:

Do you have a VNA available to you?  Or a friend with one?

No friends, but some nice folks nearby said they might help me out with the duplexer. I don't have my fingers crossed, but my other plan is to buy a full repeater.

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I run one of these that i got as payment for helping somebody out. I then sent it in to Ritron to get reprogrammed, had the duplexer retuned (it was on a business band originally), and had them enable the auto id function with my callsign. They are high quality USA made repeaters. They are low wattage 2- 5 watts, but i get 10-15 miles with an antenna only 50 feet high running at 2 watts. The other nice thing about them being low power is that they draw next to nothing for amps. I run mine with a 10 watt solar panel and a small 7ah lifepo4 battery. It's always on even during power outages. Anyway, i see them on ebay every so often for $250-$500 (compared to over $1200 new). Just make sure its one of the 450-470 MHz models. The cost for Ritron to retune/program is less than $100 with shipping and is much cheaper than buying the software and programming cable for it.

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