Jim,
If you are using an NPN transistor interface, then Writelog must be using
postive logic, not negative logic. Right? Anyway, in addition to signal
inversion, there are several good reasons to use a transistor interface.
First, the rig's keying circuit may or may not be compatible with the LPT or
serial port signal. The LPT port uses TTL logic, and so the high and low
signals are +5VDC and 0VDC respectively. Some rig keying circuits may not
like this or their higher voltage may be dangerous for the LPT port. The
RS-232 serial port standard defines high as up to +15VDC and low as up to
-15VDC. Again, this voltage swing may not be compatible with all rig keying
circuits. Therefore, it's advisable to use a transistor interface with a
+12VDC supply. Further, the current draw in the rig keyer circuit could
exceed the current rating on the LPT port or (less likely) the serial port.
A transistor interface will eliminate that danger. Finally, the transistor
interface provides extra safety in the event the key line is accidentally
shorted -- the transistor will die instead of your LPT port!
73, Dick WC1M
> -----Original Message-----
> From: Jim Brown [mailto:jim@audiosystemsgroup.com]
> Sent: Monday, December 15, 2003 12:56 PM
> To: dick.green@VALLEY.NET
> Subject: RE: [WriteLog] Several issues
>
>
> On Mon, 15 Dec 2003 12:14:28 -0500, Dick Green wrote:
>
> >Writelog's W5XD+ outboard keyer supports paddle input. It's a better
> >solution for keying and SO2R switching than the parallel port.
>
> Several thoughts. First, I find hitting <ALT><K> to call the
> keyboard to be a reasonable subsitute for having a paddle hot
> next to the computer. I've done it both ways, and while I
> prefer the paddle, the keyboard works fine. How well it works
> for you will depend a lot on your keyboard skills, and
> practice helps. :)
>
> Second, Elecraft allows both a paddle and keyer to drive the
> K2 simultaneously. I've done that, and it works fine. Their
> radio is unique in that regard, in that their keyer has the
> logic to interpret a pull to ground on both sides of the
> paddle as a straight key or keyer output, so you use diodes
> in series with the Writelog keyer feed to both dit and dah inputs.
>
> But the same concept would work with most radios if you
> connected your paddle to any good outboard keyer, with
> individual diodes connecting both the keyer and the Writelog
> keyed output to the radio. I plan to add that connection to
> connect my CK-2 to my Omni V.9.
>
> This won't help SO2R, but it's fine for SO1R. :)
>
> BTW, I use a simple NPN polarity inverter to convert the
> negative logic of the Writelog keyer to positive logic for
> the radio. But is there a good reason why Writelog can't
> provide a positive logic keyed output from its serial port so
> that the inverter is not needed? It certainly would be a lot
> easier and cleaner without that NPN and base current limiting
> resistor!
>
> Jim Brown K9YC
>
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