[Elecraft] 2 radios, 1 antenna... finally a prototype!

[Don Wilhelm]

Vic,

Such fail-safe mechanisisms can certainly be devised if deemed necessary.
The 8R signal mentioned is actually the inverse of the Amp-Key line, so that
signal can be produced with an inverter and no additional connections to the
internals of the K2.

One of the goals was to do the job with no active devices, and such
fail-safe mechanisms were not considered.

One of the ways to accomplish such 'fail-safe' operation is to inhibit
keying (or PTT) until all other conditions are properly satisfied, but the
problem with that solution is - it requires some kind of external stimulus
to initiate the transmit state for the K2 (i.e. the chicken and the egg
controversy).  If one inhibits the paddle and PTT inputs to the K2, that K2
will never enter the transmit state and activate the Amp-Keying signal - the
only way to make that work is to accept an external 'start' input, such as a
footswitch or other similar input.  The CW PTT circuit on my website
http://w3fpr.qrpradio.com does exactly that task and could be used if such
safety features are deemed necessary.

73,
Don W3FPR

> -----Original Message-----
>
> JEAN-FRANCOIS MENARD wrote:
>
> > I finally did a first prototype of an interface to link two K2/KPA100
> > on one multi-band HF antenna using Don W3FPR schematic. For my first
> > "from scratch" project, it is not too bad.
> <snip>
> > Take a look... http://homepage.mac.com/jfmenard/PhotoAlbum55.html
>
> The only thing that bothers me about this circuit is that if the Amp Key
> output from either K2 is disconnected for any reason, transmitting on
> the other one will put RF into the front end of the first one.
>
> I thought of several ways to make the circuit fail-safe with a few logic
> gates, but I'll leave it to the real circuit designers to suggest the
> best way.  I would suggest using the 8r signals from the K2s in addition
> to the amp-key output.  The 8r is on in receive mode, and you could
> arrange things so that unless either an 8r signal or amp-key ground is
> present, that K2 will always be connected to the dummy load.
>
> --
> 73,
> Vic, K2VCO
>