amp and swr high

The antenna is not the problem. In this case, it is the amplifier,with the radio only, the SWR is 1.5:1; when the amplifier is turned on, the SWR jumps. The amplifier is not only transmitting at 27 MHz, but is also transmitting on a second frequency of 54MHz. This is known as a ''second harmonic'' (2X the fundamental frequency of 27 MHz, transmitting at 54 MHz). Thus the SWR meter is reading both the reflected signal of the normal frequency and the rejected second harmonic signal. The antenna will not accept energy transmitted at higher MHz, and returns it all back to the radio, which shows up on the meter as high SWR because the meter cant tell the difference. Hope this helps. SIXX

 

Hey Sixx, in his case, is it something to be concerned of? Is that "2nd frequency" that the antenna w/n accept being sent back as heat?

 

I'm don't know about this second harmonic stuff, but I do know that there are potential problems with the antenna system that can cause this. A bad stud or the insulator between the mount and the antenna can cause this, in addition to a bad coax or a bad PL259 on the coax. Just because a coax is new doesn't mean it's good. Soldering a PL259 on is a pretty delicate process, and it's easy to melt the insulator and ruin it. It might not be bad enough to show up with the barefoot radio, but it's enough that the extra power finds its way to short to ground.

 

I guess what I'm trying to say is that everything might look fine with no-little power to it, but something is arcing or shorting with more power. Just like the battery cables on your car are just fine on you car, but would last about 30 seconds on your truck. I don't know enough to discredit this resonant frequency idea, but I do know enough to say you'd better be awfully sure that the problem is with an inaccurate reading from your swr meter, and not a problem with your antenna system.

 

Why would you try to discredit the harmonics idea ? The change here is a direct result of the amp being turned on.

The impedance mismatch as described plainly is the comparison between the impedance of what's on one side of the SWR meter with the impedance on the other side of it. The meter is seeing the amplifier next in the chain not the antenna. When the amp is keyed to take the readings it's shows reflected power being returned.
Not that grounding isn't needed( 4 gauge wire recommended for 500 watts or less), but if Kubota is seeing 3:1 the amp probably doesnt have alot of filtering and the input tuning is not an good as it could be, a common fault of no tune amplifiers.
Turbo-T also mentioned about the heat buildup which a good point also, probably not from the harmonics but the reflected power.
That would obviously would shorten the life ,due to the amp circuits wouldnt stand reflected power from a load mismatch.

 

CORRECT ....

Most CB amps are trash generators and put out strong 2nd and 3rd harmonics. Your meter will read them as a higher SWR reading.
If you have a good TVI filter put it between the amp and the swr meter and see if the problem goes away.

 

I'm not trying to discredit the harmonics, you obviously know way more than I do about it. I'm just saying it's possible something else is going on. Would Kubota be able to verify that it's just harmonics by putting the SWR meter in between the amp and the antenna instead of between the radio and the amp?

Honestly, it sounds like I'm wrong here. I just had a similar experience once where swr was fine barefoot, and through the roof with power, and it ended up that I had a bad stud. It didn't show any continuity with on the volt meter, but it was definitely bad and my swr was fine after I replaced it. It was a brand new stud, btw.