Another SWR question

[Hairball]

I use 3 different radios off the same antenna and coax system. My Yaesu and Anytone 6666 show swr's from flat to 1.2 from channel 1 thru 40. These readings are from the built in radio swr meters and my Daiwa cross needle swr meter. Readings are consistent. The Yaesu has a built in power supply and the 6666 uses a Radio Shack 15 amp switching power supply. My problem is with my RCI 2970N2. Off the same system the Daiwa meter shows swr's from 3-5 and the RCI shows 2 bars for swr. Difference is the Powermax 100 amp power supply. Could the Powermax be causing this issue? Thank you,
Hairball

 

[nomadradio]

The RCI radio most likely was made after 2007 or so, and has low-quality IRF520-type MOSFET transistors in the RF power circuits and the linear.

They have a tendency to generate more harmonic energy than transistors designed to use as RF amplifiers. Those harmonic frequencies are fooling the SWR meter. The higher reading has nothing to do with your antenna, it's just showing you "dirty" RF power that contains extra frequencies. Since those frequencies are not the ones the antenna is built to accept, they get rejected, or "reflected" and drive up the meter's SWR reading. The meter can't tell how many frequencies you are feeding into it. The wattmeter just shows you the sum total of them all.

73

 

[Handy Andy]

You may seeing reflection from the harmonics a radio that has a "built-in" amp design.

The "Built-in" amp part is where you get into trouble.

Most (if not all this RCI is another exception to this) use a type of filtering to couple stages that remove spurries and unwanted harmonics. That way, they (the stages of the TX RF amplifier section) amplify what it's designed for - not everything else inclusive.

When you build a "duck radio" meaning low power output and throw a mobile linear into a case and cobble a power supply together - you wind up with results like this.

To fix that means you'll have to "retune" the TX strip on the radio side so it doesn't produce such a wide band of harmonics - one way to do this and works for many - would be to turn down the TX RF power the radio side produces and also while doing that - watch your cross needle system - that should tell you what is really at fault for causing this SWR condition.

 

[BC Coyote]

You may seeing reflection from the harmonics a radio that has a "built-in" amp design.

This. Ranger radios with the built in amps are notorious for this. I think it comes down to inadequate shielding between stages in the radio, causing unwanted interaction between stages and generating harmonics.

 

[Hairball]

Thank you to everyone for taking the time to give such in depth explanations of my question.