We measured the deviation limits on the MD-380 with firmware from OpenRTX. Thank you to Redman for help with modifying the firmware to make this test as easy as possible.
The transmitted signal is about 10 dB down at 3000 Hz and almost gone at 4200 Hz. Therefore, there is not enough deviation for Opulent Voice.
The part of the radio under test was the HR_C5000. This is a part from Hong Rui and is a DMR digital communications chip. The chip handles 4FSK modulation and demodulation, among other functions.
According to a translated datasheet for the HR C5000, adjustment of the frequency offset range not possible. It appears to be designed only for +/- 3 kHz. Unless there’s an undocumented feature, or gain is added after the HR C5000, then +/- 3 kHz is the maximum deviation for this radio.
The HR C5000 puts out two analog signals MOD1 and MOD2, which are combined and then drive a varactor diode. The varactor might well have more range. Or it could be replaced with one that has more range.
Below is a photo essay of the testing and screenshots of results.
One Reply to “Deviation Limits of the MD-380”
Excellent. Thank you very much for sharing.