QRP Zero-beat Indicator for the Elecraft K2

This is a circuit that builds on KR5L’s zero-beat indicator circuit. He suggested trying a CMOS version of the 567 instead of the standard bipolar version, and here it is: the QRP version of his circuit. It draws only 0.9 mA at 5V compared to about 20 mA/8V for the original circuit.

Compared to the original circuit, C2 and C3 have been divided by about eight, and C1 has been divided by about two, give or take values found in my junk box.

Noise and Marker Generator

I have built the N0SS wideband noise generator. The noise generator was built in a small metal box in combination with a 1 MHz marker generator. The marker has been implemented using a simple packaged crystal oscillator.

The noise generator is used for setting up the K2 filters using a spectral analyzer program, and the marker generator is used for aligning old radios.

Trap for increasing 12 m image rejection of the K2

Several K2 owners have had interference from broadcast images. This image band overlaps with the 19 m broadcast band as found by subtracting twice the 4.915 MHz intermediate frequency. The 12 m band image rejection, before the trap modification, on my K2 was 48 dB (preamp on). It improves to 59 dB with the trap. The trap is simple to build on a small piece of board and can easily be fitted on top of the RF-board.