SWR goes up with power?

[Onthecoast]

I used a antenna analyzer to dial my antenna in exactly on a frequency. When I hook up my radio and different SWR meter, I get similar/identical readings on low power (1w DK). When I raise the variable power, the SWR goes way up, like up from 1:1 to 2:1. Is there something that I should be looking for there? I don't understand why or how that happens. The electrical connections should be good. I'm running a blue sea fuse box with positive and negative leads to the battery. The radio is a Magnum 257HP and the antenna is a Wilson 1000 mag mount.

 

[Beetle]

I used a antenna analyzer to dial my antenna in exactly on a frequency. When I hook up my radio and different SWR meter, I get similar/identical readings on low power (1w DK). When I raise the variable power, the SWR goes way up, like up from 1:1 to 2:1. Is there something that I should be looking for there? I don't understand why or how that happens. The electrical connections should be good. I'm running a blue sea fuse box with positive and negative leads to the battery. The radio is a Magnum 257HP and the antenna is a Wilson 1000 mag mount.

When you raise the variable power, do you readjust the SWR meter? I'm assuming that your meter is the type with the two-position switch and adjustment knob.

 

[W5LZ]

... and what were the readings of that analyzer when you 'dialed' in that antenna?
- 'Doc

 

[Shockwave]

The problem is the radio. Specifically its RF power amplifier. Those cheap power supply MOSFETS are the culprit. Significant output power is not on the fundamental frequency.

 

[Captain Kilowatt]

If that radio was put on a spectrum analyzer the bottom of the screen would probably look like grass growing from all the spurs.

 

[Onthecoast]

When you raise the variable power, do you readjust the SWR meter? I'm assuming that your meter is the type with the two-position switch and adjustment knob.

Yes. I am recalibrating after adjusting power

... and what were the readings of that analyzer when you 'dialed' in that antenna?
- 'Doc

Using the analyzer, I adjusted the antenna until it was resonate on my exact desired frequency. R was right at 50 +/- 1 and x=0. SWR was a flat 1:1

The problem is the radio. Specifically its RF power amplifier. Those cheap power supply MOSFETS are the culprit. Significant output power is not on the fundamental frequency.

That sucks but it looks like it might have been an issue with my coax run. Once I untangled my jumper from the radio to the meter, things improved.

 

[The Mad Scientist]

So what are your readings now?

 

[midnight special]

harmonics messing with reading. if the swr is good without the amp on it will be ok, but... bleed over will be allover the spectrum. like some one said before in other post i bet a spectrum anilyzer will show spikes all over. 73s midnight special

 

[Onthecoast]

I'm going to have to look at this more... My AM power is nearly 100w and my SSB power is around 20. Brand new Magnum 257HP. SSB had been up to 70 then seemed to creep down to 50, now it's barely 20.