[Elecraft] Paddle input with Y connector OK?

[Paul Christensen]

Barry,

You'll either need to look at the key line input section of the schematics 
for the two transceivers, or "give it a shot."  In  the past, I've used low 
voltage-drop Schottky diodes to steer and isolate two transceivers.  I now 
use a W8ZR StationPro II (SPII) and no longer have these concerns.  The SPII 
is a great station switching device and in addition to switching the paddle 
lines, it will automatically switch many other station  functions.

Here's why the problem can occur when using a simple "Y" adapter:  The 
paddle lines from most transceivers (and keyers) are often pulled up to a 
low-voltage supply voltage rail using moderately high-value (e.g., 10K) 
resistors.  When the transceiver is turned off, the supply rail may look 
like a low-z short to ground.  If an off-the-shelf "Y" adapter is used, then 
the paddle contacts are in parallel with 10K and a voltage divider is 
unintentionally created on the active paddle line since the paddle lines 
sees 10K to the active rig's supply and 10K in the rig that is "shorted" to 
the inactive power supply.  That may or may not be enough to continuously 
pull down the paddle line on the active transceiver and cause problems -- it 
depends a lot on what conditioning each transceiver is providing on the 
paddle lines.

If you find that an off-the-shelf "Y" adapter won't work, then with a little 
effort, you can try installing small Schottky diodes into the 1/4" or 1/8" 
mini plugs of a homebrew "Y" adapter.  Two diodes are needed in each of two 
plugs of the "Y" going to the transceivers: one on the dit lines, the other 
on the dah lines.    Better still...look into the SPII!

Paul, W9AC


----- Original Message ----- 
From: "Barry" <w2up at comcast.net>
To: <elecraft at mailman.qth.net>
Sent: Sunday, March 27, 2011 5:50 PM
Subject: [Elecraft] Paddle input with Y connector OK?


> Is there any reason I shouldn't make a "Y connector" so my CW paddle can
> be input to the K3 and another radio (or external keyer)?  Yes, only one
> will be on at any given time.
> Tnx,
> Barry W2UP
>
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