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Different Amp Output

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repeaterboy

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Hello operators.This ones got me.Motorola spectra uhf high power radio that does 26 amps on transmit when antenna not connected to radio.But when its connected drops to 15 amp output on transmit.It has an 18 inch RG-58 coax tail that comes out of the radio and connects to antenna coax.Would this thinner diameter tail be restricting output? And is there a way to directly connect antenna coax to radio without using tail? Like an adapter of some type. Anyone know why this would be happening? Thanks for your advice.
 

KE5MC

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max vswr

The RF output stage is complaining about no load (antenna). I would not have expected the amps to be that high, but obviously they are. Not good to key the transmitter full power with no antenna.

Every difference from the output jack to the antenna jack will have some impact on SWR. The best setup is the correct impedance cable with one connector at each end sized to fit the cable and mating jack of the radio and antenna. The antenna connection my be on a short pig-tail which I view as the same as the connector mounted directly to the antenna.

Edit: 2nd thought
Maybe you did use a dummy load to replace the antenna. Did you?
 
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KC0QNB

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NEVER transmit a radio without an antenna or dummy load attached NEVER. Also never transmit a radio on any frequency unless you are authorized to do so, and/or properly licensed. CB is the only exception.
 

zz0468

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Hello operators.This ones got me.Motorola spectra uhf high power radio that does 26 amps on transmit when antenna not connected to radio.But when its connected drops to 15 amp output on transmit.
I'll assume you're not completely daft, and ran your test into a dummy load. The lower current draw when hooked to an antenna could be indicative of a mismatch on the antenna feedline. Or... that could be normal, and the higher current draw could be a result of a mismatch when keyed into a mismatch. Bottom line, a good antenna, and a good dummy load should cause the radio to pull about the same current.

It has an 18 inch RG-58 coax tail that comes out of the radio and connects to antenna coax.Would this thinner diameter tail be restricting output?
No, not in the manner you're thinking. 18" of RG58 is not a lot of loss, and the thinner coax really just means it's power capability is less than a larger coax - but still PLENTY for what a Spectra can put out.

And is there a way to directly connect antenna coax to radio without using tail? Like an adapter of some type.
Yep. Get an adapter of some type. *shrug*


Anyone know why this would be happening? Thanks for your advice.
No. We have no way of knowing. All you're gonna get is guesses, with varying levels of education and experience to back them up. You're gonna have to trouble shoot it yourself. The difference in current draw is telling you that there is a difference in loading on the transmitter. Take it from there.
 
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