I'll guess. The way my other rigs get general coverage is to up convert to an IF that's higher than all the frequencies the radio supports. In the ICOM HF rigs I've owned (761, 775, 7800), that's around 70 mHz. At that high IF, it's difficult (expensive or unobtainium) to purchase a tight mode-specific filter (like 500 Hz wide with steep skirts for CW). So a relatively broad "roofing filter" is applied at the first IF and further selectivity is applied at the 2nd and/or 3rd intermediate frequencies (or DSP).
Although the K3 sports general coverage, I bet it gets a little touchy around the first IF frequency, somewhere in the 8-9 mHz range, where the roofing filters can be quite sharp and are available at reasonable cost. By "a little touchy" I mean that the rig's performance there might be different, or at the very least there is some clever engineering to deal with that range. Dick, K6KR -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Don Rasmussen Sent: Sunday, July 15, 2007 3:41 PM To: Elecraft Subject: [Elecraft] K3 Design After seeing the QST ads for the OMNI VI+ for so many years, where they showed the noise floor rise to cover up small signals inside your passband by larger signals outside of the passband - and knowing that the OMNI VI+ is a ham bands only rig, it seemed to indicate that any of the radios that offered General Coverage in the main receiver suffered that fault. The numbers seemed to prove that K2, OMNI VI+, Drake R4C, Corsair II, all ham band only have the best numbers as compared to the very best broadband designs - most often from Japan. The Orion only seemed to prove that one more time, the main transceiver is ham bands only with the weaker broadband second receiver for general coverage. That's a long way to go to provide ham plus general coverage unless those ham band only strips are fundamentally important. According to the early K3 info, the transmitter is broadband, the only limitation is where they place the bandpass filters and in theory they could arrange that any way they want. It would be interesting to know what the real design issues are and (no offense to Elecraft), how they were the first to find the best of both worlds. _______________________________________________ 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 _______________________________________________ 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
