RT-880 Schematics
Added 2025-07-04 07:34:28 +0000 UTCLooks like there is a GPIO on BK4819B that acts as the switch between chips; pin 30/GPIO2. This is curious as I have tested all the GPIOs on BK4819B and none of them seemed to do anything. I shall attempt it again. Even if this is the case it's still disappointing as both chips cannot receive AT THE SAME TIME. So listening to signals while the spectrum scope is running that I hoped this dual chip radio would solve? Not possible.
Another odd thing, the GPIOs I already discovered by experiment, they're reversed according to the schematic. GPIO 6 is GPIO 0, GPIO 5 is GPIO 1 and so on, this is making no sense.
What I discovered and you can verify this with the V4 diagnostic firmware
0 = HF RX Filter
1 = Unknown
2 = UHF TX Final
3 = VHF TX Final
4 = VHF RX Filter
5 = UHF RX Filer
6 = Unknown
According to the schematic
6 = HF RX EN
5 = U8 RX EN (whatever U8 is)
4 = UHF TX EN
3 = VHF TX EN
2 = VHF RX EN
1 = UHF RX EN
0 = Subtone Detect
See? They're reversed from reality. Very weird. Unless I've somehow got the bit ordering the wrong way, lol.
Comments
Yeah looks like a very early version they used to placate us. Still some useful info there but not ideal.
Marcus Dudley
2025-07-04 20:58:53 +0000 UTCOkay, I've done some more tracing through and it looks to me as though the "HF" on this thing feeds directly into BK4819A LNAIN pin. The same pin on BK4819B is inconclusive as it just seems to connect to nothing. I really don't think this circuit diagram is for the RT880/UV98 as we know it. I also note that they have blanked out the circuit diagram information block in the bottom right hand corner. However, I have managed to uncover it and it states the following. Quanzhou Ideo Electronic Technology Co., Ltd. File Name File Number IDO-UV98BKLCDSCH-HFRF Proposed Version V2 Effective Date 2025-04-14 Audit
Kelvin Hill
2025-07-04 15:34:07 +0000 UTCThere seems to be a lot that is very strange about this "RT-880" schematic. The whole of the HF side looks weird and I can't find the specific HF receiver chip. I can see what seems to be an unpopulated(?) 1080 for FM however at U106. My faith in the accuracy of this schematic has taken a bit of a nose dive.
Kelvin Hill
2025-07-04 15:17:47 +0000 UTC
