How to tune your MMDVM-based DVAP

In the recent years, personal DVAP's (digital voice access points) have become wildly popular, and for good reason. They are cheap and allow access to a plethora of digital voice modes, right from the comfort of your home. No DMR / D-Star / Fusion repeater in your area? With a personal DVAP, that's no problem.

One of the first things you should do when receiving or building your own personal DVAP, is make sure it's calibrated. There are slight differences that appear in the MMDVM radio chipset that can make it almost unusable - luckily for us a simple calibration program and offset setting can rectify this issue.

It is recommended this calibration be done with DMR, as of the three major DV modes, it's the most sensitive. If you use DMR to find your DVAP offset, it likely will work on all major DV modes - at least that is what the current thinking is aligned too.

So how do we do this? I want to credit K9NPX and his post here for most of the information. I've created a tool you can use to find the offset once you have the values you need, but as for the steps - all credit to K9NPX.

1. Create a channel on your radio with the following information:
• Frequency 433.000 MHz
• CC1
• TS1
• TG9
• Admit Criteria: Always
• In Call Criteria: Always
2. Log in to your DVAP running Pi-Star and navigate to the Configuration menu
3. Once in the Configuration menu, select Expert and then SSH Access
4. This will require you to log in with the same password you use to access the Admin dashboard
5. Make sure your radio is tuned to the channel you created in step 1
6. In the SSH shell window, type "sudo pistar-mmdvmcal" and press enter
7. Press the M key, which will set the tone to the appropriate settings as outlined in step 1
8. Pressing the space bar will begin to transmit the cal tone, which you should hear on the radio
9. Now, press "f" (lower case f) repeatedly until the tone is no longer received on the radio
10. Press "F" (upper case f) repeatedly until the tone comes BACK and is audible on the radio
11. Record the frequency displayed on the screen as your first calibration value
12. Now, press "F" (upper case f) repeatedly until the tone is no longer received on the radio
13. Press "f" (lower case f) repeatedly until the tone comes BACK and is audible on the radio
14. Record the frequency displayed on the screen as your second calibration value

You can use this tool to input your values and obtain your offset:

To enter in your offset:

1. Navigate to Configure, then Expert on your pi-star dashboard
2. Select MMDVMHost and scroll down to the Modem section
3. Enter the offset for RXOffset and TXOffset
4. Click Apply Changes

Make sure to test these values for a low BER - if higher than 1%, run the tool again.