Notes: MDS, blocking and two-tone IMD measurements made using the 400 Hz wide roofing filter. AM audio measurements made using 13 kHz wide FM filter although results were not significantly different using the 6 kHz wide AM filter. Even with the receiver EQ set for flat frequency response there is 'built in' audio roll off below 300 Hz and above 3 - 4 kHz.

While performing the AM audio measurements an unusual low level noise was noted whenever the carrier was modulated with a test tone. The noise could best be described as sounding like ignition noise in a mobile setup. The tone of the pulses change with modulation frequency and is present at all modulation levels. The repetition rate of the pulses slowly cycle in frequency ocassionally slowing to zero before starting back up again. The problem is not apparent on voice or music programming although it is likely still there - just not apparent with the quickly changing modulation frequencies. Take a listen to the following clip - you may need headphones and a high sampling rate to hear it.

K3.wav



While the K3 is one amazing receiver on cw and ssb it is rather disappointing on AM. On the transmit side, I've been unable to make the K3 modulate in excess of 90% positive on AM. Discussions with the folks at Electraft, and even a 'tweaked' software load, have not yielded any significant improvements. I was told that there are three separate ALC loops in the transmitter. I'm guessing therein lies the problem. Transmitted frequency response using the FM 13 kHz filter offers little improvement over the standard 6 kHz AM filter. As with the receiver, there's 'built in' roll off beyond the control of the operator. If K3 owners complain perhaps Electraft will look into possible improvements. As it is, it appears that AM was an afterthought and not part of the primary design mission.