[Elecraft] Keying a Hercules from K2

[Don Wilhelm]

Jim,

>From your description, the inverter you described is almost correct BUT it
won't work because there is no voltage available to it.

The output from the KPA100 is a HEXFET open 'collector' - which means it
makes a path to ground when active (transmit state) and is open during
receive.  The Amp Keying Circuit that can be added to the base K2 provides
an equivalent output even though it is a transistor collector.
You must provide a source of base current for the transistor in the added
inverter circuit.  Likewise the base of the transistor in the Hercules must
have a source of current to drive it to the ON (conducting) state.

The inverter circuit will need an NPN transistor, 2 resistors, and a voltage
source.
Connect the base directly to the KPA100 (or K2) amp keying output with a
resistor (1K to 10K) to the voltage source, connect the collector to the
Hercules input and a resistor (1K to 5K) to the voltage source.  Emitter
goes to the common connection between the KPA100 and the Hercules.

You can use a voltage source from either the Hercules or the K2 whichever is
more convenient or use another voltage source altogether as long as it has
the common connected to the Hercules/K2 common.

The cleanest implementation would be to build the inverter into the Hercules
since there is likely more room than in the K2/100.  I prefer to see
amplifiers that require an 'Low to Transmit' keying input over the '+ to
transmit' because they do not depend on an external voltage source - only a
contact (or saturated transistor collector) closure to ground.

73,
Don W3FPR

----- Original Message ----- 

> The Hercules was designed to work with the old Omni A, which generates a
pre-delay
> keying signal (the call it the "T line") that is +12v on transmit, but
transitions roughly 10
> ms before the Omni transmits. (The Omni 5 also generates this signal, but
doesn't take
> it outside the radio because later TenTec amps key differently.)  The
Hercules keying
> input drives the base of a 2N5087 through 1K, so it isn't going to draw
much current.
>
> The doc on the K2/100 says that the 8R line is high on receive and 0v on
transmit. An
> app note on the website says that this is a "pre-delay" keying signal that
transitions
> roughly 15 ms before the K2 transmits.
>
> It looks like all I need is a simple inverter (NPN, collector to the amp
keying line, emitter
> to chassis, K2 drives the base through 1K) from the 8R line to the
Hercules keying line.
> Does this make sense?
>
> My rig also includes a KPA, but I don't think I need it. It has a key
output to drive power
> amps, but there is no doc on it. Is it also a pre-delay signal (that is,
10-20 ms before
> transmit)?  What is its logic -- positive to transmit?
>
> Jim Brown  K9YC
>
>
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