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The little "trimmers" on the MPET.....

Adjustments on the MPET

Some of us like pictures. Some of us like words. Here is a tagged photo version of what the little potentiometers do on the MPET for those that missed that in the service manual.


Unless you know what you are doing. LEAVE THEM TRIMMERS ALONE. However, a few tips:

Beginner Notes:

HELPFUL TIP #1: Adjusting R350, will limit the total volume output to a speaker, regardless of what volume control you add inline. This could be helpful to know for those that may use headphones.

HELPFUL TIP #2: When you adjust R222, it will adjust total RF power output. Some of us, may choose to lower this below the nominal high power capability. When you ground pin 5, it provides a low power setting. This will now allow you to bring the low power setting even lower. DO NOT! try to adjust R222 to try to squeeze out more power than what the radio is supposed to provide.This may damage your MPET!! EXAMPLE: Maybe I want my MPET to output 100mW on "low" power and 3W on "high" power. This gives me that option.

NOTE: Its probably not a good idea to use an external adjustment for RF power as it may create spectral purity issues with your MPET, so please consider this.

Intermediate & Advanced Notes:

I have been playing around with different setting for deviation and input/output for some of the sound card and data stuff I have been doing. Anyone get this far? Wonder what you have discovered.

Lets use this thread to discuss best practices and applications regarding adjustments so everyone learns together.


  • edited April 2017

    Here is a picture to show the removed potentiometers. The volume control was removed which is 10K Ohm. The squelch 100K Ohm potentiometer was also removed.

    These will be replaced with a digital potentiometers controlled by the Arduino.

    Note: This picture is showing the 10K Ohm Digital Potentiometer.

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