Help With dBms please

Thread Starter

DrainMan

Joined Mar 21, 2020
8
I am new to all this. I am trying to measure the output power of a VTX it's a video transmitter on 5.8ghz it says it's outputting 1000mW milliwatts. When I connect it to my RF meter some of them will cause the dBms to drop more and some of the VTXs will make it rise.

It's starting at a weird number like -79.4dBm not sure why. I have an external attenuator of 30dBm on so I don't blow it up.

There is a spot to set the internal dBms not sure what for.

Any help would be sooooo appreciated thank you. 16551649728256798788878393239308.jpg16551649223622527999552016799009.jpg16551649469102497567999371101087.jpg16551649580003696967588355332274.jpg16551649728256798788878393239308.jpg
 

Papabravo

Joined Feb 24, 2006
18,806
Any time you connect something to an RF source you create a situation called an impedance discontinuity. It means that at the connector the impedance changes abruptly. When this happens some of the power is transmitted through the discontinuity and some of it is reflected back to the source. If enough power is reflected back to the source, it can damage the transmitter. Many transmitters are smart enough to detect this condition and reduce the output power to prevent this from happening. What you need are either better instruments or a smarter test setup.
 

Thread Starter

DrainMan

Joined Mar 21, 2020
8
Any time you connect something to an RF source you create a situation called an impedance discontinuity. It means that at the connector the impedance changes abruptly. When this happens some of the power is transmitted through the discontinuity and some of it is reflected back to the source. If enough power is reflected back to the source, it can damage the transmitter. Many transmitters are smart enough to detect this condition and reduce the output power to prevent this from happening. What you need are either better instruments or a smarter test setup.
Thank you so much, I am having hard time finding an instrument to measure " wattage" of a video signal. Should I continue with trying to measure dBms and then calculating it over to milliwatts or watts. If the value was -34.5 and I powered up at 800mW output on the VTX and the value changes to -29 I have 5.5dbm of power coming out. I think. Is there anyway to make sense of this for seeing if the advertised 800mW output is accurate?
 
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