Problems with band decoder

[Jim Spaulding]

I am using a Y cable from the K3 Aux port to a KPA500 and a WX0B band
decoder for a six pack antenna switch.   When the Band Decoder is added,
the KPA500 does not automatically follow band changes from the K3
although band changes on the KPA500 flow to the K3.  Has anyone else had
this problem and is there an easy fix?

Jim

W0UO

______________________________________________________________
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
Message delivered to [hidden email]

[w8fn]

You don't say, but I presume the band decoder is operating
correctly.Since the band change function of the KPA500 works, this says
that the serial data bus between the amp and the radio is working fine.
The band decoder may be loading down the 4 band data lines to the point
they don't make the logic "1" voltage the KPA500 needs. It's probably a
major pain, but try measuring the voltages on the 4 band data lines with
a DVM with everything connected and report back the logic "1" (most
positive) voltage you see on the data lines as you cycle through the
bands. The KPA500 should still change bands properly if you give it a
short shot of RF, but the situation should really be corrected.

73...
Randy, W8FN

On 7/12/2016 11:07 AM, Jim Spaulding wrote:

> I am using a Y cable from the K3 Aux port to a KPA500 and a WX0B band
> decoder for a six pack antenna switch.   When the Band Decoder is
> added, the KPA500 does not automatically follow band changes from the
> K3 although band changes on the KPA500 flow to the K3.  Has anyone
> else had this problem and is there an easy fix?
>
> Jim
>
> W0UO
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

______________________________________________________________
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
Message delivered to [hidden email]

[Don Wilhelm]

Instead of the band data lines being loaded down so the logic "1" value
is not reached, it is more likely that the RS-232 lines are not being
pulled to the logic "0" level because of pullup resistors in the band
decoder receiver inputs.

If the band decoder that you are using has pullup resistors, this may
indeed be the case.

The first K3s did not have pullup resistors in the K3 - the band decode
outputs were just FET open drain.  That meant that a band decoder was
expected to have the pullup resistors on the decoder end, but many do not.
Elecraft then added pullup resistors to the K3 outputs rather than
requiring that customers modify their band decoders.  That is not the
best solution for logic drivers and receivers (the pullup resistors
should properly be at the receiver end, not at the driver end), but it
was 'necessary' in ham circles where some devices expect the drivers to
have the pullup resistors.

Enter the KPA500 - the KPA500 went to extreme measures by adding diodes
to the band data lines to prevent damage (and confusion) for the band
data lines from devices that did add pullup resistors at the band data
receiving end and those pullups were to voltages higher than +5 volts.

So you may be faced with a situation where your band data decoder *also*
needs diodes to isolate the voltage of the pullup resistors at the
receiver from the K3/K3S band data lines.

Adding a series diode in your band decoder with the cathode pointing to
the K3 band data lines should cure the problem.

73,
Don W3FPR

On 7/12/2016 8:42 PM, Randy Farmer wrote:

> You don't say, but I presume the band decoder is operating
> correctly.Since the band change function of the KPA500 works, this
> says that the serial data bus between the amp and the radio is working
> fine. The band decoder may be loading down the 4 band data lines to
> the point they don't make the logic "1" voltage the KPA500 needs. It's
> probably a major pain, but try measuring the voltages on the 4 band
> data lines with a DVM with everything connected and report back the
> logic "1" (most positive) voltage you see on the data lines as you
> cycle through the bands. The KPA500 should still change bands properly
> if you give it a short shot of RF, but the situation should really be
> corrected.
>
> 73...
> Randy, W8FN
>
> On 7/12/2016 11:07 AM, Jim Spaulding wrote:
>> I am using a Y cable from the K3 Aux port to a KPA500 and a WX0B band
>> decoder for a six pack antenna switch.   When the Band Decoder is
>> added, the KPA500 does not automatically follow band changes from the
>> K3 although band changes on the KPA500 flow to the K3.  Has anyone
>> else had this problem and is there an easy fix?

______________________________________________________________
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
Message delivered to [hidden email]