I trust you used MEC switches !
73 Rag
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> From: Larry Tyree <n6tr@teleport.com>
> To: trlog@contesting.com
> Subject: [TRLog] Switch box
> Date: Tuesday, August 05, 1997 5:54 PM
>
>
> 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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