[Elecraft] Advice needed: Remote Station Enhancement

[Joe Subich, W4TV]

You're dealing with a "standard" that was originally developed for use
only within one company's products - much like Elecraft's Aux Bus.

As such, any "industry standard" is moot.  The design is for active
high/voltage source (to +12V originally) and was not intended for any
purpose than providing band switching for the FL-700 then the Quadra.
It would seem to me that any product that claims to inter-operate with
the Yaesu "Band Data" would emulate or at least be compatible with
that behavior - including the ability to *source* sufficient current
at +12V.

These devices are not operating in the "communications (non-ham) world",
they are strictly amateur products.

73,

    ... Joe, W4TV


On 2/27/2018 9:28 PM, Don Wilhelm wrote:
> The problem is that most devices (in the ham world) expect the driver 
> device to provide voltage.
> In the communications (non-ham) world, the expectation is that the 
> driver device produces either a logic low (short to common) or a logic 
> high ( open circuit).
> 
> Look at the data sheets for "line drivers" and "line receivers" to check 
> out what I am saying.
> 
> Open collector or open emitter does not make a difference in function, 
> it is only a circuit design decision.  Yes, open Collector (or open 
> drain) is commonly use in logic where the active state is zero volts 
> (transistor or FET conducting to ground).
> The open emitter design is the opposite.  A conducting device will 
> provide a voltage on the line (or signal) being driven.
> 
> The point is that in a properly designed communications system, the 
> drivers provide either conduction to ground or an essentially open 
> circuit to the communications line (think of a relay being either open 
> or closed).  The receiver provides the voltage to detect whether the 
> driver is in an open circuit or closed circuit state.
> If there are multiple receivers in the system, only one can be "boss", 
> and that one determines the open circuit voltage and contains the pullup 
> resistors for the system.  Other receivers work in listen mode and will 
> contain no pullup resistors or active drivers.
> 
> This whole situation goes back to the "one driver, one receiver" condition.
> Only one driver can exist on a communications system without conflict.
> Multiple receivers are possible, but only one (at the far end of the 
> line) should provide the pullup resistors.  All other receivers must be 
> only in the listen mode.
> 
> 73,
> Don W3FPR
> 
> On 2/27/2018 8:06 PM, Joe Subich, W4TV wrote:
>>
>>  > But many (most) ham devices do not do it that way, they expect the
>>  > pullup resistors will be provided by the driver gear.
>>
>> Actually, most devices that use BCD "band data" expect an open
>> emitter driver not an open collector driver.  Open emitter will
>> *source* voltage for logic high and be open circuit for logic
>> low.  This is the convention from the early Yaesu rigs which
>> were the first devices to support "band data" (it is the way
>> the FL-7000 and Quadra amplifiers operate).
>>
>> You will find the W9XT BCD10/BCD14 decoders with their opto-isolator
>> inputs work just fine with the "open emitter" drivers.  Other devices
>> designed with Yaesu transceivers in mind have appropriate current
>> limiting (series) on the input lines and "pull down" (parallel)
>> resistors on the logic gates.  Some "standard" devices (Top Ten
>> BD-Y and the original microHAM Band Decoder) will provide both
>> current limiting resistors and internal pull-ups but I have not
>> seen any amateur product with series diodes in the band data lines.
>>
>> 73,
>>
>>     ... Joe, W4TV
>>
>>
>> On 2/27/2018 4:17 PM, Don Wilhelm wrote:
>>> Knut,
>>>
>>> That is the way it *should* be, and was that way in the K3 originally.
>>> But many (most) ham devices do not do it that way, they expect the 
>>> pullup resistors will be provided by the driver gear.
>>> So, because of that, Elecraft added pullup resistors to the band data 
>>> outputs of the K3 long ago.
>>> So yes, we are left with a situation that often requires steering 
>>> diodes.
>>>
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> On 2/27/2018 3:48 PM, ab2tc wrote:
>>>> Hi Don and all,
>>>>
>>>> Hear,hear, Don. The receivers should have the pullup resistor to 
>>>> whatever
>>>> the appropriate voltage needed (within reason) *and* a steering 
>>>> diode in
>>>> series with the input. This will prevent another device with a higher
>>>> voltage from feeding current back into the device which could damage
>>>> semiconductors. Without the steering diode all receivers must use 
>>>> the same
>>>> pullup voltage. Of course a single receiver is not a problem either.
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