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Construction Manual for the K2DI v.III and K2DI-PCI boards © EA3BLQ - Revision June 2005
K2DI v.III Digital Interface
Main features:
• The circuit is the very same as the one used in v. II.2 but for an outlet of 5VDC
that has been added to supply voltage to the K2DI-PCI. The board has been
redrawn to a much smaller size: 59 mm (2 5/16") x 35 mm. (1 3/8").
• Its features include the Microphone Configuration Extender as well as a buffered,
fixed audio output and the cutting of the Front Panel microphone connector's AF
and PTT lines when transmitting data, so as to avoid the unwanted transmission
of shack noise through a live microphone.
• This board may be used as a stand alone Digital Interface by connecting J3 to a
Mini Din connector at the rear K2 panel, or as a mother board for the K2DI-PCI.
How it works:
Microphone Configuration Header Extender
All pins of J1 and J2 are connected in parallel except for the AF and PTT lines, which are
connected in parallel only while the K2 is in standby or reception mode but are cut while
transmitting digital data, as explained further on.
Through the ribbon cable, J1 receives and sends signals from and to the Microphone
Configuration Header at the Front Panel board and because of the parallel connection of J1
and J2, J2 becomes an extension of the aforementioned Configuration Header. Thus J2 is
the header where you are to configure the Front Panel Mic Connector in accordance with
your microphone’s wiring and needs.
Buffered, fixed audio output:
The received audio is fed to J4 either from Aux Audio J5 at the K2's RF Board or from pins
1 and 2 at P2 on the KAF2 or KDSP2 board.
Although I don't see any inconvenience to feed the AF signal by taping P2 at the KAF2 or
KDSP2, instead of J5 at the RF board, so as to take advantage of the filters, this is the
user's choice. In any case, care must be taken not to tape and connect the wrong pins to
J4 at K2DI board. P2 at the KAF2 and KDSP2 has the GND signal at pin 3, while J4 at K2DI
and J5 at the K2's RF board have the GND signal at pin 2. An error when identifying the
pins would produce a short. To prevent this I have modified the P2 three pins male
header so that when installed, I get the normal 3 pins male header on the bottom side of
the board while I also get a 2 pin male header on the top side (pins 1 and 2). Further on
this document you’ll find pictures showing this mod.
For consistency sake, I decided to copy the Elecraft's original K2 Audio Amplifier circuit to
feed U2, the AF amplifier (LM386N) and to control its audio level. The use of a couple of
J310 FET (Q1 and Q2), biased through a 3.3 MOhm resistor, as in the K2, is very useful as
it allows the disconnection of the AF amplifier from the product detector when on data
transmission.
(35 paginas)
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