Weird issue K3/KPA-500

[w0mu]

I am attempting to hook up an Array Solutions DBS-2 Band decoder on the
K3.  When I have it connected using a Y cable the KPA-500 no longer
follows the bands it seems to get confused.  I have the KIO rev B board
which I believe should have the pull up resistors but I am seeing 2.3 to
2.5 volts on the Band out pins.  I think this should be between 3-5
volts.  Are there KIO rev B boards that might not have been upgraded?  
SN on this K3 is 2745.

--
Mike W0MU

J6/W0MU November 21 - December 1 2011 CQ WW DX CW
W0MU-1 CC Cluster w0mu.net

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[Don Wilhelm-4]

Mike,

Your band decoder is apparently loading down the K3 band data lines to
the point where they cannot be unambiguously decoded by the KPA500.  
Yes, less than 3 volts on the band data lines is in the "noise region"
for digital logic.

You may have to add isolation diodes and pullup resistors in your band
decoder to solve the problem.

It is true that the K3 has pullup resistors, but they can only supply so
much current. Apparently, your band decoder requires more current than
the K3 pullup resistors can provide.

The solution is to add a diode at the band decoder Band 0-3 lines.  The
cathode should point toward the K3.  Then on the anode side of the
diodes, add a pullup resistor to whatever voltage is required by your
band decoder.

The early K3s "did it right" in providing open drain outputs for the
band data lines, relying on the attached device to provide the pullup
resistors.  BUT, many devices do not provide those pullup resistors -
many radios have the pullups at the driver end rather than following the
normal rules for logic circuits which place the pullups at the
receiver.  SO, the K3 added pullup resistors at the drivers.
NEXT, enter the KPA500, which now needed to provide protection for
itself from band decoders which DO provide pullup resistors (but to a
voltage higher than 5 volts), so the KPA500 added isolation diodes and
its own pullup resistors to the band data lines.  That then requires
that the high level for the band data lines be a diode drop level above
the normal high logic level.  No problem if only the K3 and KPA500 are
connected, but if a band decoder that takes current in the high level
state is connected, the K3 will not supply enough current from its
pullup resistors to bring the high logic level to an unambiguous (to the
logic devices) high level.  In other words, the band decoder you have
chosen is sucking too much current from the K3 when the band decode
lines are in a high logic level state.  The addition of diodes on the 4
band data lines (cathodes pointing toward the K3) is the only solution,
and then you will have to add pullup resistors on the anode side of the
diodes to assure (to the band decoder) that the high levels are properly
detected.

Bottom line - the K3 original design "did it right", but caved in to
popular demand because many band decoders did not "do it right".  Then
the KPA500 had to contend with devices that "did it right", but at
higher voltages than the KPA500 could tolerate - so we are back to the
original "question" of where the proper place for the band data pullup
resistors should be.  I am sorry to say that it is quite a mixed bag of
confusion since one band decoder does it this way, and another does it
that way.  Right now, the only sensible solution is to add the
protection diodes and pullup resistors to each band decoder that is
attached to the K3 and KPA500 combination.

73,
Don W3FPR



On 10/11/2011 11:08 PM, W0MU Mike Fatchett wrote:
> I am attempting to hook up an Array Solutions DBS-2 Band decoder on the
> K3.  When I have it connected using a Y cable the KPA-500 no longer
> follows the bands it seems to get confused.  I have the KIO rev B board
> which I believe should have the pull up resistors but I am seeing 2.3 to
> 2.5 volts on the Band out pins.  I think this should be between 3-5
> volts.  Are there KIO rev B boards that might not have been upgraded?
> SN on this K3 is 2745.
>
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[w0mu]

Thanks Don.

Mike W0MU

J6/W0MU November 21 - December 1 2011 CQ WW DX CW
W0MU-1 CC Cluster w0mu.net


On 10/11/2011 11:27 PM, Don Wilhelm wrote:

> Mike,
>
> Your band decoder is apparently loading down the K3 band data lines to
> the point where they cannot be unambiguously decoded by the KPA500.
> Yes, less than 3 volts on the band data lines is in the "noise region"
> for digital logic.
>
> You may have to add isolation diodes and pullup resistors in your band
> decoder to solve the problem.
>
> It is true that the K3 has pullup resistors, but they can only supply so
> much current. Apparently, your band decoder requires more current than
> the K3 pullup resistors can provide.
>
> The solution is to add a diode at the band decoder Band 0-3 lines.  The
> cathode should point toward the K3.  Then on the anode side of the
> diodes, add a pullup resistor to whatever voltage is required by your
> band decoder.
>
> The early K3s "did it right" in providing open drain outputs for the
> band data lines, relying on the attached device to provide the pullup
> resistors.  BUT, many devices do not provide those pullup resistors -
> many radios have the pullups at the driver end rather than following the
> normal rules for logic circuits which place the pullups at the
> receiver.  SO, the K3 added pullup resistors at the drivers.
> NEXT, enter the KPA500, which now needed to provide protection for
> itself from band decoders which DO provide pullup resistors (but to a
> voltage higher than 5 volts), so the KPA500 added isolation diodes and
> its own pullup resistors to the band data lines.  That then requires
> that the high level for the band data lines be a diode drop level above
> the normal high logic level.  No problem if only the K3 and KPA500 are
> connected, but if a band decoder that takes current in the high level
> state is connected, the K3 will not supply enough current from its
> pullup resistors to bring the high logic level to an unambiguous (to the
> logic devices) high level.  In other words, the band decoder you have
> chosen is sucking too much current from the K3 when the band decode
> lines are in a high logic level state.  The addition of diodes on the 4
> band data lines (cathodes pointing toward the K3) is the only solution,
> and then you will have to add pullup resistors on the anode side of the
> diodes to assure (to the band decoder) that the high levels are properly
> detected.
>
> Bottom line - the K3 original design "did it right", but caved in to
> popular demand because many band decoders did not "do it right".  Then
> the KPA500 had to contend with devices that "did it right", but at
> higher voltages than the KPA500 could tolerate - so we are back to the
> original "question" of where the proper place for the band data pullup
> resistors should be.  I am sorry to say that it is quite a mixed bag of
> confusion since one band decoder does it this way, and another does it
> that way.  Right now, the only sensible solution is to add the
> protection diodes and pullup resistors to each band decoder that is
> attached to the K3 and KPA500 combination.
>
> 73,
> Don W3FPR
>
>
>
> On 10/11/2011 11:08 PM, W0MU Mike Fatchett wrote:
>> I am attempting to hook up an Array Solutions DBS-2 Band decoder on the
>> K3.  When I have it connected using a Y cable the KPA-500 no longer
>> follows the bands it seems to get confused.  I have the KIO rev B board
>> which I believe should have the pull up resistors but I am seeing 2.3 to
>> 2.5 volts on the Band out pins.  I think this should be between 3-5
>> volts.  Are there KIO rev B boards that might not have been upgraded?
>> SN on this K3 is 2745.
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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Post: mailto:[hidden email]

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