For those of you who I have already bored with the details of my
switchbox, I apologize.
I have been building a two radio switch box with the following features:
1. Computer interference for two Kenwood radios.
2. Interface to parallel port for paddle, footswitch, CW and PTT outputs
and relay control (to switch between radio 1 or 2). The four pole
relay to switch between radios switches the CW, microphone and two
poles off of a PTT relay to the active radio.
3. Yes - two poles on the PTT relay. I brought both of them out to
phono jacks and one of them goes via the mic cable to the radio.
The extra contact might be useful if you find yourself in a situation
where you need to key an amplifier directly instead of using the
radio's amplifier control. Instead of using a transistor for PTT
ouput, the transistor drives a double pole relay.
4. I used a reed relay for the CW. This solves any problems with
positive or negative keying.
5. I put 3 leds on the front panel - +12 volts, CW and PTT. I felt these
would be great diagnostic tools in case something stops working during
a contest. I bring the +12 volts into the box via a phono jack to
a fuse, then output to more phono jacks for other station accessories.
This is a wise thing to do for safety reasons so you don't get 30 amps
flowing through a small wire if you get a short. The CW and PTT LED's
are wired to the transistor driving the respective relay.
6. I used a 5 volt regulator to power pull-up resistors for the paddle
input and footswitch input on the parallel port.
7. I used a 6 volt regulator to power my audio mixer box directly.
8. Instead of using the STROBE (pin 1 of the parallel port) to connect
to the emitter of the CW or PTT transistors, I buffered it with
a single transistor pulling down on a 330 Ohm bias resistor to a
second transistor (essentially an inverter). Some computers have
a hard time sinking current for both PTT and CW.
9. When bringing a parallel port output into the input of a transistor,
I bring it through a 1K (or about 600 Ohm) resistor, then through
a series diode and then a 10K pulldown resistor. This helps move
the required voltage on the input up some to give you better
noise rejection.
10. The Kenwood computer interface is still very easy, just hook the radio
output to the serial input, and run the computer's serial output
through a few kilo-Ohms and then a diode clamp to ground to
prevent the signal from going negative. Two circuits are required
for two radios. The Radio Shack 6 pin DIN plugs work for the radio
side.
11. Switch my R4-C to either TS-850S for critical listening.
These boxes are a lot of work! There are about a million connectors on
the back panel and over 20 components on a perf board. I had thought
about getting some made up to sell - but don't have the bandwidth. If
anyone else wants to do this, that would be great. There is probably
50 dollars or more worth of parts involved, and several evenings of
assembly. I would say the box would be a bargain at $200!
I present the above ideas for those about to do the same thing. I
I will put some of it in a future update of the manual (including
schematics perhaps).
73 Tree N6TR
tree@contesting.com
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