Elecraft KSB2 - Manual (Page 17)

17
Microphone Configuration
Follow the steps below to configure the K2 for your microphone.
1. If the Front Panel assembly is plugged in, remove the appropriate screws and unplug it. There are two
screws holding the Front Panel board to the Control board, and four chassis screws that hold the Front
Panel assembly to the chassis.
2. Place the Front Panel board upside-down on a soft cloth, with P1 to your right. P1's left-hand pins are
the K2 signal lines, while those on the right correspond to the 8 pins of the microphone jack.
3. Determine the proper P1 wiring for your mic. First look in Table 2 (following page) to see if your mic
is listed. (Also check our web site, www.elecraft.com, which lists additional microphones). If you have
a mic that is not listed, use Table 1 in conjunction with your microphone's schematic to determine
which wires to use. If your mic has the wrong connector type, you can use a Radio Shack #274-025.
4. Connect each of the required signal lines using hookup wire, wire-wrap wire, or discarded component
leads. (You can optionally use 2-pin computer "jumper blocks" for connections that tie adjacent P1
pins together.) Some mics also require a bias resistor between the AF and 5V lines, as described in
Table 1 or Table 2.
5. Plug the Front Panel assembly into the RF board. Secure it to the chassis (4 screws) and control board
(2 screws).
Table 1. P1 Signal Descriptions. (Also see Table 2.)
Signal Description Notes
AF Mic audio, Low-Z
(approx. 600 ohms).
Approx. 100 mVp-p
audio level. With some mics it is necessary to connect 5V to AF
through a resistor. The kit includes a 10 K resistor (Rbias)
for use with many condenser mics. Some mics may require
a much smaller resistor to supply operating current for a
buffer stage. Consult the transceiver and microphone
schematics.
PTT Push-to-talk Contact closure to ground when PTT button pressed.
The PTT signal is the same as the DOT key line, making it
easy to use a foot switch or other method of enabling xmit.
DN "Down" button
(optional)
UP "Up" button
(optional)
FUNC Function button
(optional)
Contact closure to ground when button pressed, otherwise
open (infinite resistance).
You can activate the VFO A/B switching function using
any contact closure to ground (UP, DN, FUNC). The
present version of the KSB2 firmware does not support
other mic button functions.
5V 5 volts DC (10 mA
max.) Some microphones will work well with 5 volts even though
the schematic calls for a higher voltage.
GND
GND Ground Signal, logic, or shield ground.