Hi Bill and Geoff, thanks for your comments.
I am sorry I replied through the elecraft newsgroup. 73 Gian I7SWX --- Geoffrey Mackenzie-Kennedy <[EMAIL PROTECTED]> wrote: > Bill, > > Gian might be suggesting the use of H-mode mixers to > replace the TUF-1 mixer > and NE602 product detector, but I have not asked > him. The H-mode mixer has a > much higher 3rd Order Intercept than either the > TUF-1 or NE602, but I would > have thought that the very good IMD performance of > the H-mode mixer would be > wasted in the K2. As I see it the IMD performance of > the 2N5109 post mixer > amplifier, variable bandwidth IF filter and MC1350 > IF amplifier (and > probably the front end bandpass filters) would > become the weak link, and > determine the overall IMD performance of a modified > K2. Also the H-mode > mixer requires a 50% duty cycle squarewave LO > injection for best IMD > performance which would require some modification of > the K2's LO and BFO > output circuitry, although this modification might > not be necessary because > of the poor (by comparison) IMD performance of the > weak link mentioned > above. > > 73, > Geoff > GM4ESD > > > On Wednesday, May 09, 2007 at 2:46 AM, Bill Coleman > wrote: > > > On May 8, 2007, at 11:11 AM, Giancarlo Moda wrote: > > > See for file: I7SWX possible changes to K2 and K1 > > RTX. It is possible you need to be a member. > > > > The documentation reports suggested changes: > > > > 1)Front-end mixer replacement and roofing filter > > addition. These mods have been implemented and > tested > > by I0CG in his K2. > > Part of the beauty of the K2 is that it is a very > simple radio, > superbly executed. (To paraphrase a comment K9AY > said to me before I > bought one) > > The K2 uses a TUF-1 balanced mixer with close > attention to the > injection levels and impedance matching. You'd be > hard-pressed to > improve the mixer performance for HF. > > Since the K2 is single-conversion, the primary > crystal filter IS the > roofing filter. The primary crystal filter is pretty > darn good for CW > or RTTY. > > > 2)Demodulator replacement. > > What would you do to replace the product detector? > Since the dynamic > range of the signals after the AGC of the IF stage > is pretty limited, > the NE602 is a pretty good choice. It wouldn't be > easy to do better, > especially at the price point for the K2. > > > > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com _______________________________________________ Elecraft mailing list Post to: [email protected] 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
