[Elecraft] Accessory Line Protection

[Don Wilhelm]

Mike,

If you have the 74154 inputs connected to the K3 band data outputs, 
nothing more should be required.  The 74154 should adequately isolate 
the inputs from whatever you have connected to the output side of the 
decoder IC.
I don't even know if the capacitors are required (or desirable), 
although since the band data outputs are not dynamically changing, they 
should make no difference.

If you have anything else connected to the K3 band data outputs (in 
parallel with the 74154), then that may be a different consideration, 
but you did not mention anything of that nature.  The KPA500 should not 
cause a problem.

If you have trouble with the KPA500 band selection, try removing the 
capacitors and see if that cures the problem.

73.
Don W3FPR

On 6/12/2013 7:27 PM, w0ih wrote:
> Well, I got a bit lazy and tired of changing antennas to my K3 so I built a
> system to automatically change antennas as I switch bands.  What I'm trying
> to accomplish is to be able to control my station remotely over the internet
> (I use TeamView which includes audio).  I'm driving a 160 meter dipole, 80
> meter dipole (my own design, tunes from 3.5 to 4.0), 60 m dipole, 40 meter
> tap off the boom of my beam, TH11DX beam and a 6m vertical (2m and 440 as
> well).
>
> Basically what I did was to build a remote antenna switch (from an April
> 2005 QST article) built from a FarCircuits.com kit (circuit board and
> relays, ~$40) as the remote switch.  I have a single coax coming the last 50
> feet from the base of my tower up to the shack.  This remote switch (grounds
> the antennas when not in use) is driven by a circuit that I build using a
> VERY old chip from my junk box, a 74154 BCD to decimal line output chip
> (decodes the K3 Accessory Band outputs 0-3 to a 1 of 16 line output).  I
> also have a manual setting that allows me to switch the antennas with a
> rotary switch - 1 to 6, so I can use it with my KX3 as well.
>
> So, my question, I have tapped off the Accessory output lines on the back of
> the K3 into the antenna controller to the 74154 chip.  I have some .01 uf
> capacitors for filtering the lines.  But my question is, do I need any other
> protection for the lines coming from the output of the K3 to my controller?
> The outputs of the 74154 drive a set of 6 5 volt relays which drive the
> lines (and LEDs) down to the remote antenna switch board.
>
> The cable from the K3 Accessory plug to the controller is shielded and
> grounded to the chassis.  There are 6 lightning arrestors on each of the
> coax inputs (copper strapped together and ground to the base of the tower).
> The six control lines from the controller to the remote antenna switch are
> also shielded and grounded (12 volts to drive the relays).
>
> But am I missing anything in protecting the K3 lines to the controller?
> I've checked the schematic of the K3 but can't find much on the outputs for
> protection.
>
> Incidentally, I do also have a KPA500 that is also connected to the system
> Accessory output.
>
> Mike
>    W0IH
>
>
>
> --
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