SWR issues with more power..

[Captain Kilowatt]

I tend to agree with 453.
Remember this amp is operating in class C and is probably producing some harmonics.
73
Jeff

Ahem..........No Jeff. It IS producing harmonics.

 

[314]

I've said this a few times, nobody has to follow suite just an idea. I just check/tune my SWR at the antenna with the coax I'm using, 18ft , 32ft etc. I run no swr/power meter inline with an amp, swr at the antenna should not change or if just a very little once antenna is tuned/setup. I've had good luck for over 20+ years doing it, harmonics used to ruin my day, until I took out that 3ft, 6ft jumper and my power meter. I do check it "at"the antenna every so often, or after a good storm. A good swr analyzer "at" the antenna should point almost everyone in the right direction

 

[Woody-202]

With my AT-6666 on low I get a flat SWR (3.5w) , on high
(14w dk) I get like 1.2:1, when I kick on the Palomar 400 I get 65w dk on AM (medium) but like 2.75:1 SWR.

This is with the external meter just after the amp.

The radio built-in meter says 1.2 as well when amp is off.. when amp is on it says like 1.6:1..

Now when on SSB and medium on amp, I get a nice swing (upto 300w or so) and external meter only hits like 1.4:1 and the internal radio SWR meter says 1.2-1.3 with modulation.. which looks fine to me..

I agree with some of the other comments. Several decades ago a friend of mine ran into issues when he ran his rig into an amp (then to the antenna) and was using the radios internal SWR meter only. With the amp inline the meter was only checking the SWR between the radio and the amp, so it always looked good to him. A meter put in after the amp showed why he ended up damaging his gear (4:1 or maybe more). It was a good enough of an example for me, and I've used external amps ever since, and always after the last device in-line before the antenna.

 

[CB590]

Radio is new AT 6666. Never been clipped or modded. Actually just put on scope and adjusted for a clean wave.

Set for 48w pep in AM and SSB.. per the tech when on max power and 18w pep when on low for both also. Low dk on AM was set for 3w..

I'm leaning toward the ground and choke theory.

All else aside I don't run AM hardly at all. And on sideband I talked last night and all reports said I sounded good/great.

 

[undertaker]

Analyzer is the way to go.. Had my MFJ for years works just fine..

 

[999]

Radio is new AT 6666. Never been clipped or modded. Actually just put on scope and adjusted for a clean wave.

Set for 48w pep in AM and SSB.. per the tech when on max power and 18w pep when on low for both also. Low dk on AM was set for 3w..

I'm leaning toward the ground and choke theory.

All else aside I don't run AM hardly at all. And on sideband I talked last night and all reports said I sounded good/great.

What external meter are you running, and do you have to calibrate it, or is it automatic? If not, do you recalibrate at the higher power level?

 

[543_Dallas]

I've said this a few times, nobody has to follow suite just an idea. I just check/tune my SWR at the antenna with the coax I'm using, 18ft , 32ft etc. I run no swr/power meter inline with an amp, swr at the antenna should not change or if just a very little once antenna is tuned/setup. I've had good luck for over 20+ years doing it, harmonics used to ruin my day, until I took out that 3ft, 6ft jumper and my power meter. I do check it "at"the antenna every so often, or after a good storm. A good swr analyzer "at" the antenna should point almost everyone in the right direction

It works. My first experience with this was a palomar 450 hd. The swr was over 3:1 with the amp on no matter what I did. I tried everything and didn't know what else to do. I finally gave up and just ran it that way. It never blew up and sounded fine. I replaced that amp a few years later with a 4 pill xforce and the problem was gone. This was back around 2004 when xforce had standards.

 

[Shadetree Mechanic]

The output tuning might need to be adjusted. I would be curious to see if it has the same problem on a dummy load.

 

[543_Dallas]

The output tuning might need to be adjusted. I would be curious to see if it has the same problem on a dummy load.

It could be a result of output tuning. I used to think the swr would be high if the output tuning of the amp was off. The db finally set me straight.

The swr meter doesn't have a clue how the output tune of the amp is. It only knows how much power is going forward and how much is reflected. For those who remember ccm he once said "turn the tune knob on a tube amp and watch the swr". The swr doesn't change unless the amp starts to oscillate. Oscillation creates the harmonics and they give the false high swr reading.

Even the most problematic amps seem to work fine on a dummy load because the harmonics are not reflected by the load.

 

[CB590]

What external meter are you running, and do you have to calibrate it, or is it automatic? If not, do you recalibrate at the higher power level?

MFJ-822 meter. Does 0-30 and 0-300w.

I use the higher 300w scale when running the amp.. heck even without, the SSB on high hits 45-50w

 

[M0GVZ]

Radio is new AT 6666. Never been clipped or modded. Actually just put on scope and adjusted for a clean wave.

Set for 48w pep in AM and SSB.. per the tech when on max power and 18w pep when on low for both also. Low dk on AM was set for 3w..

I'm leaning toward the ground and choke theory.

All else aside I don't run AM hardly at all. And on sideband I talked last night and all reports said I sounded good/great.

It doesn't need to have been clipped or modded, it just has to have the mic gain set up too high and that'll produce a wide splattering signal.

I'm not leading towards the choke theory because I run an Imax 2000 with a RF choke inches below the feed point and the SWR remains the same whether I'm running 4W into it from a CB or 400W into it from my ham gear.

 

[CB590]

It doesn't need to have been clipped or modded, it just has to have the mic gain set up too high and that'll produce a wide splattering signal.

I'm not leading towards the choke theory because I run an Imax 2000 with a RF choke inches below the feed point and the SWR remains the same whether I'm running 4W into it from a CB or 400W into it from my ham gear.

I could also have a crap A99. Been this way since I got it just about a year and half ago.

Whenever I run power this has swung my SWR. First in PA and now here in NY. Different coax too..

 

[999]

Do you have a ground rod in the ground?

 

[CB590]

Do you have a ground rod in the ground?

No ground rod for antenna mast. I asked about running a wire down from the mounting point earlier on and someone said it would act like a counterpoise..

 

[Shadetree Mechanic]

Here is some info about station ground.

https://helpdesk.flexradio.com/hc/e...aradigms-Facts-and-Fallacies?mobile_site=true