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====== Using a UV-K5 as a POCSAG Transmitter ======

**TL;DR:** you definitely need a modified firmware, you can download it [[https://mega.nz/file/1iojHRIZ#fjHAN5ZlLTDFRU-lsSnyyGZaZiBh2BudWOIsaymBTp8|here]] and flash it on Chrome/Chromium using [[https://egzumer.github.io/uvtools|this tool]]. Set the RX modulation to "DIGI", bandwidth to "WIDE". A hardware mod might be required, your mileage may vary. For more details, keep on reading.

Quite widespread nowadays, the UV-K5 is a fantastic platform for many experimentation. However, fast (aka 9600 baud or flat audio) data was out of reach as the filters and pre/de-emphasis was always on by default, same as many other Chinese radios. So no DMR, NXDN, M17, DSTAR... Or POCSAG!

However, some time ago, Rob Riggs WX9O from Mobilinkd figured out how to modify the radio's registers and hardware filters to get a very flat audio response from this radio. A few capacitors must be replaced and shorted, and a custom firmware has to be flashed.[[https://github.com/mobilinkd/uv-k6-digital-mod/blob/master/UV-K6.ipynb|More details here]] [[https://www.youtube.com/watch?v=oMhtGjtORUk|and here]]. 

This is perfect for almost all digimodes... Except POCSAG! Sadly, even with those mods, the radio doesn't have the required deviation (+-4.5kHz) for DAPNET. 

This is just a matter of tweaking the registers of the RF chip; REG_40 of BK4819 handles deviation... Specifically [[https://github.com/mobilinkd/uv-k5-firmware-custom/blob/e1e2fea2290451f35fe67b65742ee48c799d4798/driver/bk4819.c#L1217|at this exact line when in "WIDE" mode.]] Setting the value after the | to 0x1470 seems to yield the best results.

If you don't feel like re-compiling the firmware yourself, here is a pre-build copy, you can directly [[https://mega.nz/file/1iojHRIZ#fjHAN5ZlLTDFRU-lsSnyyGZaZiBh2BudWOIsaymBTp8|download it here]] and flash it on Chrome/Chromium using [[https://egzumer.github.io/uvtools|this tool]].

Don't forget set "demodulator" to DIGI and setting the bandwidth to wide! 

You can then hook up your radio to your favorite POCSAG modulator (Unipager or MMDVM), adjust your levels for an optimal 9kHz deviation, and enjoy your 5W, cheap DAPNET transmitter!.

{{::photo_5859290464077858799_y.jpg?400|}}

You __might__ me able to get away with just the firmware flash... The filter hardware mod just corrects the lower end of the frequency response, it might just work with just the modded firmware!
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