> When tuning across an AM station there are clicks and cracks, seems > to be on even kHz. On my radio it has been from day one. Is this > normal or is my radio faulty? I use latest FW. / Jim
Jim, When tuning near a very strong continuous carrier, you may hear a small AF artifact at points where the PLL divider switches. This occurs at different intervals depending on the band. On 20 meters the interval averages about 15 kHz. We minimize the effect by introducing a small amount of DSP limiting during the switching window (~10 ms). This is not avoidable with the present synth design, which was optimized for extremely low phase noise. There are two contributing factors. First, we follow the DDS with a very narrow crystal filter to dramatically clean up this signal; frequency shifts through the filter are subject to a small amount of group delay. (Other rigs using DDS use either no filtering, or very wide filtering, leaving them susceptible to DDS spurs.) Second, the VCO control bandwidth is low, improving close-in phase noise, but again causing a small re-lock delay when the PLL dividers are switched. (Most rigs use a wider VCO control bandwidth, and thus suffer from greater phase noise at small offsets that are important to ham operation, i.e. < 2 kHz from the carrier.) We feel that this was the right design tradeoff, and I think most customers would agree. Dynamic range is greatly improved with a low- noise synthesizer, both on transmit and receive. 73, Wayne N6KR ______________________________________________________________ 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
