XPR 45XX low transmit power

[smorris]

Good morning everyone. I built a homebrew GMRS repeater using an XPR4500 and an XPR4350. The repeater works well. The issue is the TX power. I have the TX radio set at 48W, which is the max and low power set at 20. The TX radio is only putting out 31.5W. I was curious, so I swapped them around and tested the other radio and got 30.5W. I thought it might be a bad PA, however, when a PA goes bad, the power out is usually around 1W or less. The SWR is 1:1 and the reflected power is only 0.0215W.

 

[KevinC]

Are you measuring power after the duplexer?

 

[smorris]

Are you measuring power after the duplexer?

Power out after the duplexer is 20W on both and the SWR and reflected remain the same.

 

[KevinC]

Ok. Are you accounting for your test cable loss?

 

[smorris]

Ok. Are you accounting for your test cable loss?

The length of the patch cable is only 18in. I just tested an XTL5000 for power out and I'm getting 43W when set to 45.

 

[mikewazowski]

Since you mentioned GMRS, I'm assuming you're measuring power out in analog and not digital?

 

[smorris]

Since you mentioned GMRS, I'm assuming you're measuring power out in analog and not digital?

Yup, analog.

 

[KevinC]

I see the UHF version is rated for 40w, maybe setting it to 48 is over driving something. Try setting it to 40w and see what happens.

 

[kayn1n32008]

The power output has likely been reduced by the previous owner.

 

[kayn1n32008]

Any chance that the radios were acquired from Canada? Max power output for a LMR mobile station in Canada is 30w.

 

[Project25_MASTR]

Put the radio in field service mode and see what it outputs for high power on the various analog frequencies.

Typically a bad idea to go above what the radio is actually rated for (just because it says 48W doesn't mean it is actually capable of putting 48W out). Also, depending on what kind of Wattmeter you own and how it's set, that may be a perfectly adequate error in display.

 

[smorris]

Well, thanks for the feedback! I’m not sure if these were used up north. I’m using a relatively new digital meter. When I put the repeater in low power mode(20W), I get 13W out. So it seems the reduction in power is proportional. I once had a CDM1250 VHF that was rated for 45W and I got it to put out 52W with no issues.

 

[N1GTL]

Power out after the duplexer is 20W on both and the SWR and reflected remain the same.

Measure the output power directly out of the radio into a dummy load. That will eliminate an antenna and a bad/mistuned duplexer.