On Feb 10, 2009, at 2/10 9:09 AM, wayne burdick wrote: > While it is possible to attenuate some spurious responses by moving > coax cables around, there is a firmware-based approach that we're > working on. The general idea is to shift the 1st LO and BFO a small > amount, simultaneously, when the VFO is tuned to specific frequencies. > If the shift is small relative to the communications bandwidth in use, > it will hardly be noticeable when the VFO is tuned over a "mapped out" > spot in the tuning range.
When you do this, will you be exposing the "real" 1st LO frequency through CAT? Some of us are using the LP-PAN to receive and demodulate, while using CAT to move the transmit VFO around in the spectrum of the LP- PAN to zero beat a 2 kc baseband signal to the signal that is being demodulated. As it is, there is already a problem with the SHIFT knob moving the 1st LO frequency, but effect that can be discovered with CAT, and as long as SHIFT is not changed during transmission, it is workable. The real way out is to not use the SHIFT knob at all; we don't really need the shift knob when we implement our own DSP demodulators behind the LP-PAN. If the 1st LO were to move by itself, we would need to know where these magic frequencies are. One possibility is that if you only plan to nudge the receive VFO, we can just keep our receive VFO fixed to a non-magic frequency and always tune the receiver by offsetting into the LP-PAN's output. The best would be an option to be able to choose not to nudge the 1st LO. Speaking of the SHIFT moving the 1st LO frequency, does the SHIFT knob also move where the birdies occur? I haven't installed my second receiver yet and cannot perform the experiment. 73 Chen, W7AY ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
