John, KD2BD wrote: There may be more than just two...
http://www.qsl.net/kd2bd/ksb2.html It looks like many of us have been down the same road. ---------------------------------------------------- As I understand the evolution (having followed it since I built S/N 1289 in 2000): 1) The K2 was designed with a minimum-bandwidth SSB filter. The Filter provided an audio bandwidth of barely 2 KHz. The idea was that narrower bandwidths provided the best signal/noise ratio - a very important issue for QRP operation especially. 2) It was discovered that a number of early SSB filters were significantly narrower than 2kHz, severely impacting their performance on SSB. The problem was traced to too much variation in the characteristics of the crystals being received from the Elecraft vendor. Elecraft changed their specifications and matching process to ensure adequate consistency. They also replaced crystals in anyone's K2 that exhibited poor bandwidth. 3) John, KI6WX, developed several different mods for the OPT1 filter which allowed widening the bandwidth of the filters to more closely approximate what other Ham SSB rigs use. This was especially popular after the KPA100 was released, allowing higher power for the non-QRP operators. These mod kits consist of different sets of coupling capacitors that are used with the original Elecraft crystals (it's important to use Elecraft crystals that were shipped after the specifications were tightened - see 2 above). The information is on the Elecraft web site. Kits of capacitors are also available from Elecraft if the builder doesn't have the right ones handy. 4) The issue of audio gain has come up from time to time since the K2 was released. The gain is actually a composite of audio and RF gain to produce 10 watts or 100 watts PEP (it is not recommended to exceed those power levels on SSB in any event because the harmonic distortion levels increase quickly). That's why a QRP K2 often shows just barely a full 10 watts output on 10 meters, while it easily produces more than 10 watts on, say, 40 meters. Monitoring the transmit ALC action one sees that often only one bar barely flickers on 10 meters while several bars flash on 40. What's happening is that the transmitter RF strip has lower gain on 10, so more output from the balanced modulator is needed there. Some mics don't drive the audio chip hard enough to produce full output on the bands were the transmitter strip RF gain is lower. Again, John, KI6WX, and others came up with mods to improve the levels for full output with mics that were marginal when used with the K2. Other operators used external amplifiers with lower-level mics. Those mods are also documented on the Elecraft web site. 5) Now it appears that there are some questions about the audio QUALITY produced by the audio portion of the K2 that Jim, K9YC, is exploring. Elecraft has always encouraged builders to tinker and improve on the K2. Many of the improvements to the K2 design that have been made over the years have come from just such efforts, such as the filter mods by John KI6WX. (Actually John has been responsible for several other significant mods as well.) What Jim, K9YC, and others are doing pursuing better audio quality is in the best tradition of Elecraft builders and tinkerers. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com