Minimum Power for SWR?

[Riverman]

My SWR meter requires 4 watts for accurate SWR measurements.

Are we talking about the transmit power minus the slight loss in the coax jumper?

Or is total coax loss included? For example, if using a 50' length of RG8X (and 3' jumper) at a frequency of 144.0 MHz, the resulting power is only about 3 watts, which is less than the 4 watts required for accuracy.

 

[Captain Kilowatt]

Minimum RF power specs for SWR meters usually refers to the power required for full scale deflection in the calibrate mode when setting the meter to the far right of the scale. Try it and see. If you can properly set the meter then you are good to go. You must be measuring at the antenna end of the cable are you to consider line losses. What are you using for a meter to measure at 144 MHz?

 

[Riverman]

Minimum RF power specs for SWR meters usually refers to the power required for full scale deflection in the calibrate mode when setting the meter to the far right of the scale. Try it and see. If you can properly set the meter then you are good to go. You must be measuring at the antenna end of the cable are you to consider line losses. What are you using for a meter to measure at 144 MHz?

Thank you, Captain.
That makes perfect sense. Was making it more complicated than it is.
Am using a Diamond SX-200. (1.8 - 200 MHz)

 

[Captain Kilowatt]

Cool. I was just wonder about the meter because some think you can use a CB meter on VHF and usually that is NOT the case.

 

[vkrules]

No the line attenuation will only result in a slightly lower reading. (like maybe 1.1 to1 to 1.2 to 1 ) and that would be the same no matter what power you used.

If you have a long enough run of cable even an open circuit will show 1 to 1. Used to see that all the time with poor commercial VHF and UHF installs.

You are probably right though there is most likely a point where the power is to low for a reverse reading. I mean excessive loss on the feedline with 4 watts., as apposed to just straight loss. And raising the power level would help.

 

[vkrules]

With CK on FSD. was just looking at the "other side of the coin."

 

[Paul-W5lz]

Typically, that meter is going to be close to the transmitter. If there isn't all that much cable between the transmitter and the meter, there's going to be very little loss of any kind, so, if your transmitter is putting out enough power to calibrate that meter, then that's all that's required.
Wanna know what it read -at- the antenna? Put the meter at the antenna. that can be a trick all by it's self, right? Oh well...