An Elecraft re-post information on how to put the K2 on 60 meters for those who are anxious to try out the band without the K60XV optional module. K2 firmware does not at present include 60 m in the band map, so the modification works by "sharing" 40-meter components.
Note: This modification is recommended for experimentation only. However, a few hams in the UK have made these changes successfully, and Elecraft own initial tests show that performance is the same as on the other bands.
1. The 40 meter band-pass filter must be resonated on 60 meters:
Install a DPDT switch on the rear panel, close to the 40-m band-pass filter. The two switch commons should be wired to either side of C6, the top coupling cap in this filter. In the 60 m switch position, a 4.7 pF capacitor should be placed in parallel with C6. From either side of this capacitor to ground, you'll need a 50 pF trimmer and a 47 pF fixed cap, in parallel. The filter will be peaked later.
2. Memories can be set up for easy 60m or 40m access:
Turn on the K2 and switch to 40 meters. Select the 1-kHz-per-step VFO tuning rate and tune the VFO down from 40 m to the center of the 60 meter band (~5.3 MHz). Hit A=B to set both VFOs to this frequency, then STORE the setup in a frequency memory (I used #5 since this is 5 MHz). Then tune back up to 40 meters, hit A=B, and STORE this in another memory (#7 makes sense: 7 MHz). Now you can jump to either 60 or 40 meters using the RCL button. Of course you could assign up to 5 memories for use on the new channelized 60-meter assignments.
3. The VCO requires additional capacitance:
Use RCL #5 to get back to 60 meters. The PLL will be out of lock because the 40-meter VCO capacitance is too small to allow the VCO to tune down to 5.3 + 4.9 = 10.2 MHz. To get the PLL to lock, you'll have to parallel some 30-70 pF of extra capacitance across C71. Connect a voltmeter to R30, and find a value of C that results in a VCO voltage of 1.5-7.5 V over the desired 60 m segment. Then install a tiny SPST switch on the board which, when thrown to the 60 m position, puts this cap into the circuit. Use very short leads, and cut an access hole in the bottom cover. (Note: the K60XV will be supplied with two MV209 varactor diodes, D19 and D20, that will work in combination with the K2's new "D19" menu entry to change the VCO tuning range so that it covers both 40 and 60 meters with new VCO relay combinations. You don't need new K2 firmware to use the fixed capacitance method described here. But if you have it, leave "D19" set to "N".)
4. With both the VCO and BPF switches in the 60 m position, and a 60-m memory recalled, align the BPF trimmers on 60 meters in RX or TX mode.
5. The K2's original 40-m low-pass filter and push-pull PA does a decent job of suppressing the 2nd harmonic on 60 meters, but if you want some extra margin, use the new 40m/60m elliptic low-pass filter components shown in the Revision D K2 manual. These components are already present in K2s s/n 3000 and up.
You're now ready to use the K2 barefoot on 60 meters (up to 15 W). Remember to use upper sideband *only* as we haven't yet convinced the FCC to let us use CW.
The KAT2 and KAT100 automatic antenna tuners will both work on this band, so you can use a 40 or 80-meter antenna or a random wire.
DO NOT use the KPA100 on 60 meters unless you have the means to check 2nd harmonic suppression. Since the KPA100 uses a 40/30 meter low-pass filter, the 2nd harmonic attenuation on 60 meters would be determined solely by the balance of the PA strip, which may or may not meet FCC specs. A future modification to the KPA100 will allow use on 60 meters. (Also note the carefully-defined 50-watt power limit on this band. See http://www.arrl.org for details.)
73 - Petr, OK1RP