[Elecraft] Advice needed: Remote Station Enhancement

[Don Wilhelm]

John and all,

This is a problem caused by the "way things work".
The original K3 did not have pullup resistors on the band data lines 
(correct by engineering practices, the pullup resistors should be in the 
receiving device).
BUT as a concession to those band decoders did not implement pullup 
resistors in their decoders, Elecraft got a lot of "flack" because the 
K3 did not work with those decoders.

As a result Elecraft added pullup resistors in the K3.  However those 
pullup resistors only work with devices which will respond to the +5 
volt high level.

There are some band decoders that DO provide pullup resistors, and some 
of them tie the pullup resistors to +12 volts.  Those band decoders will 
not work with the K3/K3S unless the pullup resistors in the band 
decoders are removed AND that the band decoder will respond to a +5 volt 
level for the logic high.  The result is that the K3 and band decoder 
"fight" for the logic high level.

IMHO, the original K3 design "did it right", and the problem lies with 
the band decoders.  The K3 addition of the internal pullup resistors 
caused problems with all except those band decoders that did not have 
internal pullup resistors.

73,
Don W3FPR

On 2/25/2018 9:08 PM, John Nogatch wrote:
> I had difficulty with the Unified Microsystems BCD-14, i.e. the CMOS
> inverter IC was overheating.
> 
> I eventually received the following advice from AB3CV, which I found to work.
> 
> -John AC6SL
> 
> 
> From: Jim Miller <jim at jtmiller.com>
> Date: Sat, Dec 26, 2015 at 7:06 PM
> Subject: Re: [Elecraft] K3 and Band Data
> To: John Nogatch <jnogatch at gmail.com>
> 
> 
> My BCD14 purchased this summer was unreliable as well. If you look at
> the K3 (or K3s...the same) the Band Data outputs are open collector
> pulled up by 2.2K in series with 200ohms. I knew this could be a
> problem with anything which wasn't properly buffered so I looked at
> the BCD14 schematic. I found the BCD-14 online schematic differed from
> the unit I had after inspection with a ohm meter and magnifying glass.
>