AUDIO FILTER REGISTERS

[WHIZZKIIDD]

Hello! I have tried to find settings to disable or change the low-pass options for RX, Is there any way to change the lowpass audio filter to 4.5kHz ?? And TX too if possible. I would like to extend to TX-RX 4.5KHz for a repeater. When fpassing through audio using the same Fc, The -3dB point becomes -6dB. I want to configure it to maximum audio frequency range to fully preserve the original Audio bandwidth

[ValdikSS]

Take a look at this mod: https://github.com/mobilinkd/uv-k6-digital-mod/blob/master/UV-K6.ipynb

Overview of Changes

The hardware changes which are documented below allow passing low-frequency, wide, flat baseband between the digital modem and the radio's RF chip. This is an absolute necessity for digital baseband modulation.

The firmware changes adds a new Digital (DIG) mode which does the following:

Eliminate pre-emphasis on transmit and de-emphasis on receive.
Eliminate the TX & RX 300Hz sub-audio channel high-pass filter which is used for CTCSS and DCS.
Eliminate the TX & RX 3000Hz low-pass audio filter.
Bypass the transmit low-pass filter.
Disable the MIC AGC and the ALC (limiter).
Disable squelch.
Keep MIC ADC enabled in RX mode to establish and maintain proper DC bias of the MIC input.
Enable MIC ADC during init for a short period to establish proper DC bias of the MIC input.
Reduce turn-around time from ~140ms to less than 80ms by leaving the audio amplifier enabled during TX. This also reduces a DC offset error at start of RX. The cost is some wasted current use during TX.

Note that the EGZUMER firmware, on which these changes are based, already reduces the turn-around time of the stock UV-K6 firmware from over 350ms to around 140ms.