Comtech 23cm ATV transmitter modification – replace voltage regulator

For 23cm Amateur TeleVision (ATV) I am using a Comtech 23cm transmitter powered by a 13.8V power supply.

This article tells why and how I replaced the voltage regulator.

As standard my transmitter had a L7812CV voltage regulator fitted. The datasheet for this regulator says it requires a minimum input voltage of 19V and maximum of 35V to provide a fixed output voltage of 12V. See the L7812CV datasheet here.

Because I am using a 13.8V power supply this provides substantially less voltage that the minimum input.

I have therefore replaced the voltage regulator with a Texas Instruments LM2940CT-12/NOPB, LDO Regulator (Low Drop Out).  RS Components stock number 533-5626.

This linear voltage regulator is able to operate with a small input-output differential which makes it suitable for the Comtech modification. Other benefits of this latest generation LDO regulator is it offers quiescent current levels and reduced output noise.


Firstly I removed the bolt securing the regulator. I then de-soldered the L7812CV voltage regulator using soldering iron and copper braid. With only three legs it is quickly removed.


After cleaning the board with PCB and flux cleaner I soldered the new LM2940CT-12/NOPB LDO voltage regulator to the PCB. I then secured it using the nut and bolt.


And that’s this modification complete.

Why not take a look at my YouTube channel here or Twitter posts here.

You can also register for my website here.


73 de M0NWK

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