[Elecraft] KRC2 Band Decoder

[Don Wilhelm]

Radio Amateur N5GE wrote:
> To make sure I have understood correctly.  Am I correct in saying each
> of the control wires going to the switch box should be connected to
> the SOURCE and the ground connected to the SINK?
>
> Thanks again,
>
> Tom, N5GE
> K3 #806, K3 #1055
> XV144, XV432
> W1 and other small kits.
> http://www.n5ge.com
>   
>
Tom,

While following this thread, I was thinking that someone would ask that 
question.
The answer is "not quite".  In your particular case, the ground wire 
from your relay box connects to one of the KRC2 "G" connectors (and the 
power supply common for the relays must also connect to a "G" connector) 
- your relay box requires power directed to the relay to be operated..

For some antenna relay boxes one terminal of the relay coil is connected 
to a voltage that matches the relay coil requirements (12 volts is usual 
for amateur equipment) - and the operating switch connects the other 
side of the relay coil to ground when that relay is to operate.  If your 
antenna relay box is of that type, then you would connect the relay 
coils to the appropriate SINK in the KRC2.
In other words, the relay box contains the power for the relays, and the 
switch in the shack connects the ground for the relay to be operated 
(the power provided by the relay box goes "down the SINK drain").
Don't forget that the relay power supply common must also connect to the 
KRC2 (at one of the "G" connectors).

Other relay boxes contain no power, and all the relays in the box have 
one of the relay's coil connected to ground - and the relay positive 
coil terminal must have power delivered to it (SOURCED) to operate.
This is the case with the Ameritron RCS-8VX switch.  The relay that is 
to operate must be provided with 12 volts, all the relays are connected 
to ground.  So you would connect the relay power supply to the KRC2  "V" 
connector (and power supply ground to "G:) and the wires to the relays 
to the appropriate band (SOURCE or high side) outputs - those are the 
ones silkscreened on the board *without* the bar across the top of the 
label.  Since in this case the relay power required is 12 volts, you can 
connect the relay (and KRC2) power to the coaxial power jack instead of 
to the "V" and "G" connectors.  If the relay voltage is greater than 15 
volts, you *must* use the "V" and "G" connectors when using the SOURCE 
drivers in the KRC2.  Be certain the relay common is connected to the 
KRC2 "G" connector to complete the common path.  In this case, the power 
for the relays comes from the relay power supply (that is equivalent to 
the city water supply in Jack's analogy) and is controlled *to* a 
particular relay by the source driver (that particular faucet) connected 
to the relay coil.

While one *CAN* use both the source and sink drivers together, normal 
usage will use one or the other.

As an aside, I might mention, that those familiar with relay logic might 
see a vast variety of possibilities for doing relay control using both 
the source and sink drivers, since the drivers may be "wire ORed" 
together.  Add a few diodes to help with the isolation and a lot of 
logic functions can be performed with the KRC2 outputs and some relays.

This was intended to be informative, not confusing.  If you found it 
confusing, ask about it and I will try again.

73,
Don W3FPR