Elecraft K2 PLL - Manual

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K2 Temperature-Compensated PLL Reference Upgrade
Rev. E, March 24, 2005
Description
This upgrade kit significantly improves the stability of the K2’s VFO, reducing drift per unit of
temperature by as much as 90%. It is especially useful with a K2/100, since operation at higher power will
cause faster heating inside the cabinet. The circuit, designed by John Grebenkemper, KI6WX, uses a
thermistor to temperature-compensate the varactor diodes in the PLL reference oscillator.
All parts used in the upgrade are installed on a small PC board that substitutes for resistor network RP3 on
the RF board. (See photo of installed thermistor board on page 4.) You can assemble this small board now
(see page 2), or when it is needed during assembly of the K2. All related manual changes are shown below.
If your K2 is not yet assembled, make the following changes to the Owner's manual:
On page 47, right column, last step: Make a note to install the thermistor PCB assembly at the
location of RP3, rather than the original resistor network.
On page 50, left column, first step: Make a note to use only the 12.096 MHz crystal supplied with
this upgrade kit, which is marked ECS 12.09-CD (there may also be a lot number, which can be
ignored). Your K2 may have been supplied with 1 or 2 crystals of a different type. Only one crystal is
now needed (X1). X2 will not be used.
On page 54, right column, second step: Make a note to substitute a 12-H inductor (supplied with
this upgrade kit) for the original 10-H unit supplied with your K2 for use at L31.
If your K2 serial number is lower than 3000, you should first install the BFO mod kit (Elecraft part
number BFOMDKT). The BFO modifications are already present in K2s with serial number 3000 and
higher. NOTE: The BFO mod kit originally included a 12.096 MHz crystal for use in the PLL reference
oscillator. This crystal is now supplied with the PLL upgrade kit. However, if you installed the crystal from
the BFO mod kit, you will probably not have to remove it. This is covered in the PLL upgrade kit
instructions.
Upgrade Kit (E850138) Parts List
Ref Description Qty Part #
RF-L31 12H Shielded Inductor 1 E690019
RA 33K 1/4W Resistor (org-org-org) 1 E500057
RB 12K 1/8W Resistor (brn-red-org) 1 E500089
RC 2.2K 1/8W Resistor (red-red-red) 1 E500088
RD 1.8K 1/8W Resistor (brn-gray-red) 1 E500087
RE, RF 10K 1/8W Resistor (brn-blk-org) 2 E500092
THM Thermistor, 10K, 3% (small orange body
with black and brown stripes near leads) 1 E500091
RF-X1 Crystal, ECS 12.09-CD 1 E850007
MISC Thermistor PC Board 1 E100152
MISC #24 Green Wire, Insulated 1 ft (30
cm)
E760008