[arm-allstar] Baofeng COS without opening the radio

Steve Mobley - WB4BXO wb4bxo at mindspring.com
Tue Mar 5 10:20:30 EST 2019

Bad news on the 888 and really surprised to see how much cheaper they are than the other models. 
I’m not sure I’d worry about it going away though on existing models. Per the UV-5R schematic there is a 100 MFD blocking cap but there is a 1K resistor across it, so I’m betting it was done on purpose to facilitate some accessory that Baofeng or someone makes, like the repeater cable you can get on Amazon or Radiodity. I always assumed those used VOX until I discovered the DC on the audio, which may well be its purpose.

Steve Mobley - WB4BXO
--- hello, I am an iApp-oholic...

> On Mar 4, 2019, at 11:11 PM, Doug Crompton via ARM-allstar <arm-allstar at hamvoip.org> wrote:
> OK, First the good news. This clearly works on the UV82.  With a 47K load
> resistor the voltage out is above 2V on signal reception and 0 volts on no
> reception.
> The bad news is that on the 888 it appears to be capacitively blocked. On
> initial key it ramps up to over 1.5V but then in about 5-10 seconds of
> steady signal it goes back down to zero. There were many iterations of the
> 888 and it is possible some versions are OK but if any don't work it is not
> a good fix.
> There are several options here and I have not discussed it with George
> since these findings. I doubt we will want to pursue this unless we take
> the 888 out as a purchase item offering only the UV82 in the Yellow box.
> The idea is to make the modification easier but if the 888 does not work
> that leaves the alternative UV82 and UV5R. The UV5R is about twice the
> price of the 888 currently $24 at Amazon and the UV82 slightly more. They
> do offer dual band operation which the 888 does not have.
> I have two major concerns about this mod in general. One is the fact that
> it is just poor engineering that this is happening at all. There should be
> an internal blocking capacitor. I hope it is not just bad caps leaking!
> Should Baofeng decide to add a cap on a future model the method is gone.
> The other issue is that the volume is not fixed and you cannot monitor the
> frequency by just turning up the volume independent of the Allstar level. I
> could possibly live with this problem but without COS the 888 is not going
> to work.
> I am not saying this would not be a reasonable method now for certain
> Baofeng radios but there is no guarantee this will work in the future. I am
> not sure what George will want to do regarding the manufacture of anything
> on this knowing the 888 will not work but I will be talking to him in the
> next few days about it.
> *73 Doug*
> *WA3DSP*
> *http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*
> On Mon, Mar 4, 2019 at 2:25 PM "Steve Mobley - WB4BXO via ARM-allstar" <
> arm-allstar at hamvoip.org> wrote:
>> Fred, I don’t have a 888 but I have an 82 that it works fine on. I believe
>> it to be a characteristic of most of the Chinese radios.
>> Steve Mobley - WB4BXO
>> --- hello, I am an iApp-oholic...
>>> On Mar 4, 2019, at 1:46 PM, Steve Mobley - WB4BXO via ARM-a

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