>From the SoftRock Lite build guide<http://www.wb5rvz.com/sdr/sr_lite_ii/02_lo.htm> - I guess this could explain what we're seeing:
Sub-harmonic Sampling Alan, G4ZFQ points out that on the 30m, 20m, 15m receivers, the Local Oscillator produces a signal that is 4/3 times the desired center frequency as opposed to the 4x the center frequency output for the lower band models. "Subharmonic" works like this:- The LO outputs a 13.5MHz signl that goes to the dividers /4, resulting in 1 3.375MHz square wave ( rich in odd harmonics) being fed to the mixer. At the mixer, a strong 3rd harmonic is present on the clock inputs, along with the fundamental of 3.375 MHz. The 3.375 fundamental multiplied by 3 yields the third harmonic of 10.125MHZ. The Bandpass filter (BPF) performs the essential function of severely attenuating any signals centered around the 3.375MHz fundamental frequency and first harmonmic, but allows 30m signals centering around the third harmonic of the 3.375MHz LO output. The result is that the mixer is dealing with signals in the passband, centering on 10.125MHz, as though the dividers were passing a fundamental frequency of 10.125 to the mixer. BPFs are all that stop Softrocks from working on unwanted frequencies 73, Thomas M0TRN On 24 January 2012 13:08, John/K8AZT <k8azt...@sbcglobal.net> wrote: > I have not been monitoring this mail list much recently so I apologize if > this > subject has been discussed previously. > > I like to monitor the reversebeacon.net website while calling cq or just > monitoring looking for a qso. Recently I have discovered a situation > which has > me puzzled and I am hoping someone here might be able to give me some > insight > what might be happening. > > When calling cq (CW) on 7.0 MHz cw, I see several hits on the reverse > beacon > website on 7.0 MHz, however I have also seen a couple stations allegedly > hearing > me on 10.1 MHz (2 occurrences) and a station hearing me on 28 MHz bands (1 > occurrence). I am hoping this is a problem with the skimmers, but want to > check > out if there is anything which might not be right with my K3 and/or antenna > which might be generating unwanted radiations. At the moment I do not have > exact frequencies where I was being monitored. I just thought someone > might > have a suggestion where do I proceed. > > At the moment I do not have access to a frequency analyzer, but hope I can > find > one to borrow locally. > > Thank you for any suggestions/comments anyone in the reflector might have. > > 73, > John/K8AZT > K3/ SN 1693 > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
