Impedance Lawmate?

[swake 0]

Hello, I am French so sorry for my bad English.
How to measure the input impedance of an emitter lawmate 2.4Ghz 500mw?

Thanks

[Mr.RC-Cam 117]

Your question needs clarification. Do you want to [1] measure the video input's impedance (connection to camera) or [2] do you want to measure the RF output's drive impedance (connection to antenna)?

[1] Video Input Impedance: The vTx should be internally DC terminated with 75 ohms. This low input impedance allows practical measurements with a common ohmmeter.

[2] RF Output (drive) Impedance: Not a hobby friendly measurement, requires expensive test equipment. See "Load-Pull" discussion in this document:
http://www.nxp.com/assets/documents/data/en/application-notes/AN1526.pdf

Regarding RF Output impedance, it is more common to measure RF power at 50 ohms impedance. This measurement requires a good RF power meter. For most of us, this is better than knowing the precise RF drive impedance since the power meter will report the actual RF power the transmitter will deliver into a properly designed antenna.

[swake 0]

"This low input impedance allows practical measurements with a common ohmmeter."

How should I place my ohmetre?

[Mr.RC-Cam 117]

Disconnect camera and battery power. One meter lead on vTx's ground, the other lead on the vTx's Video Input. A properly designed vTx will be about 75 ohms, which is an industry standard.

Since your are interested in the video input impedance of a Lawmate vTx, I recommend reading this old discussion (posted in 2007):
https://www.rc-cam.com/forum/index.php?/topic/2344-lawmate-tx-input-impedance/

 

[swake 0]

I found 330ohms.

[Mr.RC-Cam 117]

Sorry to hear that.