User Manual

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U P G R A D I N G T H E E L E C R A F T K 2 T O R E V I S I O N B

Rev. E, April 29, 2003

In October, 2002, the K2 transceiver was updated to incorporate many modifications that had been recommended by

Elecraft or our customers. Any Revision A K2 (or Revision XC, 1999 Field Test) can be brought up to Revision B by

making the changes listed in Table 1. K2s with serial numbers 3000 and higher already include all of the changes

(except the recent PLL Upgrade, which is also discussed in this document). To determine which revision of the K2 you

have, look at the RF board, near "ELECRAFT" label at the center.

Most of the items needed are supplied with the K2ATOBKT mod kit. Other mod kits and parts must be purchased

separately as indicated in the table; these kits come with their own modification instructions. Step 9 (AF GAIN control

modification) does not require a mod kit, but you'll still need to obtain the associated application note (see page 8).

If your present K2 firmware is older than revision 2.00A, you'll need a firmware upgrade (part # FWK2MCIO)

in addition to any hardware mod kits. New firmware installation and realignment will be done in steps 11 and

12, after all desired hardware changes have been made. This ensures that calibration and test steps will only

have to be performed once.

Table 1. Modification Steps

Modification Steps (do in order)

Board(s) Part # Pg.

1. Firmware Revision Check and Parameter Save RF n/a 3

2. PLL Frequency Stability at 7182 kHz RF K2ATOBKT 5

3. Misc. RF Board Changes RF K2ATOBKT 6

4. 15/17 meter and 20/30 meter Band-pass Filters RF K2ATOBKT 7

5. BFO Temperature Stability RF BFOMDKT 7

5A. PLL Upgrade (Temperature compensated reference osc.) RF E850138 7

6. VFO ALC and 10/12 meter Band-pass Filter RF E850093 8

7. Second Crystal Filter Flatness RF XFILMDKT 8

8. First Crystal Filter Grounding RF n/a 8

9. AF GAIN Control Smoothness All three n/a 8

10. Misc. Control Board Changes Control K2ATOBKT 9

11. Firmware Installation Control, RF FWK2MCIO 10

12. Alignment and Test Control, RF n/a 10

13. Speaker Grille Cloth n/a E850089 15

NOTE: Not included are Rev. B board changes that accommodate the K60XV 60 meter adapter (RF board: VCO and

40-m low-pass filter). The K60XV manual describes these changes, which should not be made until the option is

installed. Also not included are minor changes that have no impact on operation or performance (for example, RF

board: R60 bias pot changed to a fixed 100-ohm resistor; Control board: switch S1 changed to a jumper block, P7).

Summary of content (15 pages)

PAGE 1
UPGRADING THE ELECRAFT K2 TO RE VISION B Rev. E, April 29, 2003 In October, 2002, the K2 transceiver was updated to incorporate many modifications that had been recommended by Elecraft or our customers. Any Revision A K2 (or Revision XC, 1999 Field Test) can be brought up to Revision B by making the changes listed in Table 1. K2s with serial numbers 3000 and higher already include all of the changes (except the recent PLL Upgrade, which is also discussed in this document).
PAGE 2
K2ATOBKT Mod Kit Inventory The parts supplied with K2ATOBKT mod kit are listed below. Other mod kits referenced in Table 1 include their own parts lists. Ref. RF-C33 RF-C68 RF-C28,C29 RF-CPLL RF-C174 RF-C30,C36 RF-C91 CTRL-C12 RF-CRF, CTRL-C31 CTRL-C42 RF-D10 RF-R50 RF-R64,CTRL-R6 RF-R1, R2 CTRL-R12 CTRL-R7 RF-RREFA, RREFB RF-R11 RF-R18 RF-RFC11 RF-RFC15 CTRL-L1 Misc. Description Capacitor, 2 pF ("2") or 2.
PAGE 3
Supplemental Menu Parameters: The D I S P L A Y switch is used to access additional parameters when editing certain menu entries. These include sidetone source (S T L entry), 8R Hold mode (T - R entry), Auto-Detect mode (I N P entry), and Fan mode (P A entry, secondary menu). These will be set up appropriately during new firmware installation (page 10) and do not need to be recorded here. 1.
PAGE 4
Filter and BFO Settings (C A L F I L , Table 5)4: Before recording filter/BFO data, switch to any of the lower bands (160-17 m) so LSB/USB settings won't be swapped in CAL FIL. Connect the internal frequency counter cable to TP2 (BFO). To access filter and BFO settings, tap M E N U , scroll to C A L , hold E D I T to access the parameter, and change it to F I L . Hold E D I T again to activate the C A L F I L function. Record filter bandwidth settings (e.g. 0 . 7 0 ) for each mode and each filter.
PAGE 5
2. PLL Frequency Stability at 7182 kHz Whenever the VFO is tuned to the 5 kHz band segment centered at about 7182 kHz, the PLL reference oscillator and VCO will be at exactly the same frequency. At this point, on a small percentage of K2s, coupling between the two oscillators can result in a "wavering" quality on both transmit and receive. If your K2 exhibits this symptom, it must be corrected. It compromises signal quality, and may prevent VFO linearization (CAL PLL) from working correctly.
PAGE 6
3. Misc. RF Board Changes Add CRF (.047, "473") on the bottom of the RF board as shown in Figure 4. One trace cut is required. (This capacitor is important if you have a KBT2 internal battery or KPA100 module. It prevents damage to the K2's low-pass filter relays in the event that the AUX RF and AUX DC cables are reversed. On the Rev. B RF board, the capacitor is C224.) This step describes all RF board changes not covered elsewhere. Parts can be found in K2ATOBKT. Turn the K2 off.
PAGE 7
4. 15/17 m & 20/30 m Bandpass Filters If you have an older K2 (Rev. A or XC), you may have installed a large capacitor (150 pF or larger) at C174 due to inadequate BFO range. Increasing only the size of C174, without a proportional increase in C173, may cause excessive BFO injection and is no longer recommended. Restore C174 to its original value if applicable (82 pF; supplied with K2ATOBKT.) See descriptions below. Band-pass filter realignment will be done following all hardware and firmware updates.
PAGE 8
6. VFO ALC & 10/12 m Bandpass Filter i In the following step, be careful not to overheat the crystals. Use a temperature-controlled iron, and limit soldering time to about 3 seconds per soldering attempt. This set of modifications enhances the VFO ALC circuit and narrows the 10/12 m filter. Without the mods, a small increase in VFO spurious output will sometimes occur when switching bands to or from 10 meters.
PAGE 9
10. Misc. Control Board Changes Sidetone Modification These changes improve various operating characteristics of the K2, as explained in each of the steps below. The parts for these changes are included in K2ATOBKT. These optional changes provide a more pleasantsounding sidetone. Locate capacitor C24 (.0027 µF), which is on the right side of the Control board between RP7 and RP3. As shown in Figure 6, cut the trace on the top side of the board between C24 and pin 6 of RP7.
PAGE 10
AGC Threshold Control 12. Alignment and Test R1 on the Control board sets the AGC threshold, which also establishes the K2's I.F. gain. On Rev. A and Rev. XC Control boards, R1 is fixed. A small number of K2 owners found that reducing the size of R1 slightly could optimize the AGC threshold setting and/or bring up the I.F. gain, so we used a trimmer at R1 on the Rev. B board. Re-Installation of Boards and Panels Reinstall the front panel assembly.
PAGE 11
Supplemental Menu Parameters PLL Reference Oscillator Range Test The D I S P L A Y switch is used to access additional parameters when editing certain menu entries. Set up these parameters as follows: This test is necessary if you made the Temperature Stability modifications or changed any other components in the PLL reference oscillator. Test your sidetone using the S T L menu entry. If the sidetone is missing, E D I T the S T L parameter, then tap D I S P L A Y to change the sidetone source.
PAGE 12
BFO Test If your BFO range is slightly less than 3.6 kHz, and/or the low frequency is higher than 4912.7, your BFO crystals probably have higher than average Q. You can safely compensate for this by increasing the size of C174 and C173 in the BFO circuit. The Temperature Stability mod kit (BFOMDKT) includes two capacitors for this purpose, 47 pF to parallel with C174, and 120 pF to parallel with C173.
PAGE 13
VFO Linearization I.F. Amplifier Alignment This procedure will be necessary if you installed new firmware or if you installed the PLL Upgrade (or made other changes in the PLL area of the RF board). The procedure will be done only on 40 meters. It should not be repeated on each band. If you made the recommended modification to the second crystal filter, L34 will need readjustment. L34, located near the right front corner of the RF board, is used to peak the output of the I.F. amplifier.
PAGE 14
Receiver Pre-Alignment, 10-30 meters Transmitter Alignment, 10-30 Meters This step is necessary if you made any changes to the 10-30 m band-pass filters (steps 4, and 6, page 8). If you didn't make these changes, continue with FineTuning Filter Settings, page 15. Set the POWER control for 2.0 watts. Connect a dummy load at the antenna jack. Switch to 30 meters. Adjust L8 and L9 for maximum power output in TUNE mode. Avoiding using TUNE mode for more than 5 seconds at a time.
PAGE 15
Fine-Tuning Filter Settings 13. Speaker grille cloth Grille cloth (part #E850089) can optionally be added to your original K2 top cover. (The KPA100 module already has grille cloth for its speaker.) You can optionally fine-tune your BFO settings for each mode by ear or by using a computer-based tool such as Spectrogram. Remove the speaker from the top cover. This may involve removing the battery option (KBT2) or other top-cover options.