[Elecraft] [K3] Band data problem

[Joe Subich, W4TV]

Jim,

 > The problem comes when I add the KPA500. The RCS12 continues to read
 > and follow the band changes from the K3 but the KPA500 switches to 5.3
 > (60m) and stays there regardless of K3 front panel switches.The KPA500
 > also operates properly when the cable is connected to the Y connector
 > but not the RCS12. So the cable is not at fault.

It is likely that the RCS-12 is loading the band data lines preventing
the KPA-500 from seeing the data from the K3.  This has been reported
before ... you may want to look in the archives for a solution:
    http://mailman.qth.net/pipermail/elecraft/

I do not remember if the solution is as simple as blocking diodes in
each line or if the RCS-12 requires a high impedance line driver for
isolation.

73,

    ... Joe, W4TV


On 11/23/2012 9:39 AM, Jim Miller wrote:
> I've recently added an MFJ RCS12 controller to my K3/KPA3 setup and
> I'm having some problems.
>
> I've built and checked the BANDDATA cable and it only has the four BCD
> lines plus ground. I'm using the Elecraft Y-cable and Keyline
> interrupter. (The KEYOUT signal is connected to the KPA500 via the
> supplied RCA cable directly. This will change of course as the RCS12
> becomes operational and again when the KAT500 is added...) The RCS12
> reads the BANDDATA <0-3> lines and switches the relay outputs as
> expected.
>
> The problem comes when I add the KPA500. The RCS12 continues to read
> and follow the band changes from the K3 but the KPA500 switches to 5.3
> (60m) and stays there regardless of K3 front panel switches.The KPA500
> also operates properly when the cable is connected to the Y connector
> but not the RCS12. So the cable is not at fault.
>
> The K3 and RCS12 respond properly to the front panel band selection
> switching of the KPA500 but the KPA500 doesn't change from the 60M
> indication.
>
> It seems that the KPA500 is reading zeros on the K3 band data outputs
> yet capable of sending via AUXBUS band data change requests to the K3
> which is then transmitted via the BANDDATA <0-3> lines to the RCS12
> yet the KPA500 remains stuck at 60M.
>
> My K3 is serial number 1210 and further reading of the K3 owners manual shows:
>
> "BAND0-3 provide band selection signals. Their behavior is controlled
> by the CONFIG:KIO3 menu entry (see below). Band data is based on VFO
> A. Earlier K3s may require external pullup resistors to 5 V on these
> lines, typically 2.2-10K."
>
> BTW, I have a KIO3A and since it is the interface to the AUXBUS and
> BANDDATA I would have guessed that it has sufficient drive and pullup
> to do the interface without external pullups. Correct?
>
> So it appears the KPA500 is reading band data rather than AUXBUS and
> finding a value of zero. This may be the result of inadequate pullups
> on the K3. I thought AUXBUS was bidirectional and the KPA500 would
> have been using that for its band info input.
>
> I'm soon adding a KAT500. Since the KAT500 outputs AUXBUS to the
> KPA500 I'm wondering if it does any buffering? If so I could pass the
> K3 to the KAT500 which presumably would read the BANDDATA <0-3>
> properly then pass it along with sufficient strength to drive the
> KPA500 as well as the RCS12 correctly. There aren't any schematics yet
> for the KAT500 to determine this.
>
> Thanks
>
> jim ab3cv
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