Gmrs repeater

[WRVY769]

Hi I'm looking for some help with my gmrs repeater I have 2 KG1000G and a 50watt duplexer my swr meter shows I'm only putting out 31watt out of 50 on both transmit and receive and I also have a problem with transmitting with a radio programed to the rep15 channel you have to speak very loudly to here it on an another radio?

[OffRoaderX]

For the power, are you measuring the power directly out of the radio, or out of the duplexer?

For the low-volume radio, are you certain that the radio programmed to the rep15 channel is transmitting in WIDEband, and that both your KG-1000s are also set at WIDEband?

[gortex2]

Who tuned the duplexer ? Is it tuned for the channel you are trying to use ? What duplexer is it ? Are you testing into a dummy load or antenna ? 

[SteveShannon]

8 hours ago, WRVY769 said:

Hi I'm looking for some help with my gmrs repeater I have 2 KG1000G and a 50watt duplexer my swr meter shows I'm only putting out 31watt out of 50 on both transmit and receive and I also have a problem with transmitting with a radio programed to the rep15 channel you have to speak very loudly to here it on an another radio?

You’re only putting out 31 watts on transmit as well as receive?  On receive your SWR/wattmeter should show nothing.  Presumably one radio is set to be the transmitter and one is set to act as the receiver with the two radios both connecting to the duplexer, the transmitter connected to the 462.xxx input and the receiver connected to the port that allows 467.xxx to pass.  The third port on the duplexer goes to the antenna.  As @gortex2 alluded, the tuning of the duplexer is key to getting everything working together. Where is your SWR/wattmeter connected? If it’s directly connected at the output of the transmit radio, it should be closer to 50 watts, but probably still somewhere in the 40s.  If it’s connected at the 462.xxx input of the duplexer the wattmeter will read whatever power is left after cable losses.  If it’s connected at the antenna side of the duplexer it will reflect insertion loss through the duplexer as well as cable losses to the duplexer, and if you connected it at the antenna it will read losses through two different cables as well as insertion loss through the duplexer.  And finally, if you connected the wattmeter at the 467.xxx port of the duplexer you shouldn’t see any power at all.  

What kind of coax are you using?  What’s the length?  What kind of duplexer is it? If you’re measuring at the output of the duplexer, and depending on the type of duplexer, 31 watts out could be reasonable.

As @OffRoaderX commented the low audio could be caused by transmitting narrow band and receiving it on a radio set for wide band.

[WRVY769]

my cable is LMR 400 with 65ft of cable to the antenna. My duplexer is XLT Communications GMRS Mobile Duplexer (50 Watt) from buy two way radios.

[SteveShannon]

27 minutes ago, WRVY769 said:

my cable is LMR 400 with 65ft of cable to the antenna. My duplexer is XLT Communications GMRS Mobile Duplexer (50 Watt) from buy two way radios.

LMR-400 loses 2.8 dB/100 feet or 1.82 dB at 65 feet. 
The insertion loss for that duplexer (from the B2WR website) is 2 dB.
1.8 plus 2 is 3.8 dB, so you lose 58% of your power between the radio and antenna. 

Here's a discussion about that same duplexer from about a year and a half ago:

 

[WRVY769]

I get 50watts out of the radio and about 38 to 42 from the duplexer to the antenna.

[gortex2]

You did not answer who tuned the duplexer, but 50 in and 38 out appears accurate. You will never get 5 out f the duplexer. 3db of loss in 1/2 your power. So if it was 3db loss you would have 25 watts out of duplexer. Without proper test gear we don't know accurate insertion loss and can only go by published specs. What do you feel it should be putting out ? 

 

[Radioguy7268]

It's very common for newer folks to be in love with horsepower numbers. More watts must = more better, right? I mean, I got a 50 watt radio, so getting 45 watts out of the duplexer would mean I'm getting the most bang for my buck.

Here's the thing:  Balance & performance of the system is more important than power out. If you lose isolation (meaning more of your transmit power "leaks" over into the receive path) - then your repeater will fail to hear a weak receive signal that has now fallen below your (self-induced) noise floor. The dB loss in the transmit path is usually very closely related to the sharpness of those skirts. In other words - you give up a little in loss to gain more isolation & get deeper notches.

I will also point out that if you're transmitting out to 4 or 5 watt portables, anything more than 10 watts out of the duplexer is probably just wasted energy. Unless you wanted to create an over-blown 1 way paging system, where people can hear you 20 miles out, but they can only talk back once they get within 5 or 10 miles. If you had test equipment, you would also find that any measured de-sense (the amount of transmit power getting through your tuned notch & into the receiver) would drop as your transmit power is lowered.

Tuning a duplexer for max power out is usually counter-productive. No matter what the advertising says.