Making Un-Modules:
removing modules without rework
Mark J. Dulcey, KE1L ( )

The K2 modules (KSB2, KNB2, K160RX, KAT2) add useful capabilities to the K2. However, there are times when you might want to remove one or more modules from your K2. Installing many of the modules requires that you remove jumpers and/or components from the RF board of the K2, so you can't remove the modules by simply unplugging them. I do not yet have the KIO2 or the KAF2, so I have not yet designed Un-Modules for those modules.

The usual procedure for removing a module is to unplug the module, and then put back the removed components and jumpers. If you are permanentely removing the module, that's fine, but you might want to take it out temporarily, for any of the following reasons:
Enter the Un-Modules! By building these simple circuits on header connectors, you can remove one or more modules from your K2 without any need to modify your RF board. The Un-Modules are simple and inexpensive to build, too!

Using Un-Modules isn't quite equivalent to removing a module by the other procedure. The leads to the jumpers and components are longer than if they were soldered to the RF board, so signal leakage and stray inductance and capacitance will be higher. They should be good enough for most purposes, however.

By the way, you don't need to build an Un-Module for the KAT2. But I cover removal of it anyway.

Please let me know if you build the Un-Modules, and if you find them useful. If you have any comments or suggestions, I'd love to hear from you.

What you'll need

First, you'll need appropriate header connectors. You want headers with a single row of pins, spaced at .100 inch intervals. (There are now also metric headers with pins at 5mm spacing, you don't want those.) The ones used by Elecraft in the K2 are made by Samtec ; they can be bought directly from them, or from a number of distributors, including Arrow and Pacer . Unfortunately, the distributors that are most friendly to small orders from hams, Digi-Key and Mouser , do not carry them. Fortunately, alternatives are readily available. You can either buy headers of the exact lengths needed, or buy a single large header strip which you can cut to length. Gold-plated headers are preferred, as the K2 uses gold-plated sockets. The Un-Modules in the pictures were built using a Mill-Max 800-10-064-10-001 pin header strip (Digi-Key ED7264-ND); this strip has 64 pins, which is enough to build all the Un-Modules with some left over for possible future KIO2 and KAF2 Un-Modules.

You will also need the components that you removed from the K2 RF board when you installed the modules, or equivalent components. (I used new parts from my collection.) Finally, you will need short lengths of bare wire, such as component leads.

To build the Un-Modules, you'll need a good soldering iron (the one you used to build the K2 will be fine), diagonal cutters, needle-nose pliers (to bend the component leads and to hold the components while you solder), solder, paint or nail polish, and a small vise to hold the connectors while you build.

To prepare for installation, remove the top cover of your K2. You will not need to remove any other covers unless you're installing the Un-K160RX; that one requires removal of the heat sink. (But read the directions first!!)

The Un-KSB2


To replace the KSB2, you'll need to build three Un-Module parts. You will need the following:

1 12-pin header
2 3-pin headers
1 .001uf ceramic capacitor (C167)
2 bare wires

The .001uf capacitor is soldered between pins 7 and 12 of the large header. Each of the small headers gets a jumper wire soldered between pins 1 and 3. Mark the pin 1 end of the long header (I used orange nail polish, left over from Halloween); it goes toward the left side of the K2 when plugged in. The small headers can go in either way, so I didn't bother to mark pin 1 of those.

To install the Un-KSB2, first remove the KSB2 (carefully). Plug one of the small headers into J9, and the other into J10; both are near the right of the space the KSB2 occupied. Plug the large header into J11, with pin 1 toward the left side (viewed from the front) of the radio.

If your K2 has any filter settings configured to OP1, they will not work with the KSB2 removed. (The receiver will be very insensitive if you choose any such filter.) If you're planning to keep the KSB2 out of your radio, you may want to use the filter calibration procedure to change those settings back to using the standard variable filter.

The Un-KNB2

Un-KNB2 (front view)  Un-KNB2 (rear view)

Replacing the KNB2 requires just one Un-Module, but you do need to solder three components to it. (The pictures above show front and rear views of the same Un-Module.) The parts list:

1 8-pin header
2 470-ohm 1/4 watt resistors (R88 and R90)
1 100-ohm 1/4 watt resistor (R89)

Solder 470 ohm resistors between pins 1 and 2, and between pins 5 and 6. Position the resistors toward the back of the header. (This is important; if they point toward the front, the Un-Module will bump into the KSB2.) Then solder the 100-ohm resistor between pins 1 and 6, going over the top of the header. (Again, you're avoiding the front.) Mark pin 1.

To install, remove the KNB2, then plug the Un-Module with pin 1 toward the left side (viewed from the front) of the K2.

The Un-K160RX


This is the simplest of the Un-Modules to build. The parts list:

1 16-pin header
1 bare wire

Solder the bare wire between pins 1 and 7. Mark pin 1. You're done!

The installation of the Un-160RX, on the other hand, is the most involved of the Un-Modules, mostly because the K160RX is physically inconvenient to take out. Basically, to get the K160RX out, you have to reverse the process that you used to install it. (See the K160RX manual.) And after you're done, you will need to redo the 80-meter transmit alignment if you plan to use that band. Because this one is such a pain to install, I haven't actually tested it, but I am confident it will work.

Removing the KAT2

Since you didn't have to make any changes to the RF board (other than installing the Aux RF connector) when you installed the KAT2, you don't need an Un-Module. If you just want the KAT2 out of the circuit for testing, all you have to do is unplug the AUX RF connector from the RF board, and the control connector from the control board. Then take the cover off the main antenna input, and you're set. On the other hand, if you actually want the KAT2 out of your radio (it is the heaviest of the modules), you'll have to reverse the procedure you used to put it in. (See the KAT2 manual.)