Jump to content

Attention: RC-CAM.com will be closing down August 2021.

The RC-Cam.com forum was the very first online community dedicated to the advancement of wireless video cameras on radio controlled (R/C) models. This is now called "FPV" (First Person View). We are proud of the contributions that our members have made to the FPV hobby.

We've seen significant changes over the last twenty years. Initially there were a lot of eager R/C hobbyist that built their own video systems. Allowing these creative individuals to share their work was the purpose of this site. Now the FPV market is flooded with low cost systems; Sadly DiY FPV video projects are now rarely discussed.

RC-CAM.com (main site and forum) will be closing down August 2021. This is being announced now (March 2021) so that everyone has time to download any information that is important to them. After the site is shutdown the information will no longer be available here.

We appreciate every member's involvement with advancing the FPV hobby. It is indeed sad to say goodbye to all our online friends. Be safe and stay healthy.



Recommended Posts

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.

  • Like 1
Link to comment
Share on other sites

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/

 

Link to comment
Share on other sites

  • 1 month later...

Unfortunately that will adversely reduce the amplitude of the video signal. If the vTx has a video level POT, and you have the proper test equipment, then you can re-calibrate the video level to the industry standard 1Vpp amplitude.

Traditionally you would need a o-scope to check and calibrate the video level. But now there is an alternative -- This cool DiY Project was specifically created to check FPV video levels:
https://www.rc-cam.com/forum/index.php?/topic/4126-diy-fpv-video-calibration-tool-low-cost/

 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...