Don wrote: >I would not regard 100 Hz of drift in the K1 as a design problem at all - >The K1 spec is for drift less that 200 Hz after a 5 minute warmup. > >The fact that the K1 does not use a DDS vfo is not a 'design problem' >as was stated...
I wholeheartedly agree. I had been using (and still use) three of SWL's wonderful DSW-series mono-band DDS rigs before I got my K1 in late 2000. I was fully prepared to be disappointed by the stability of the LC VFO design of the K1. Instead, I quickly found that I was very pleased with the stability of the K1's VFO. > but surely was a design decision based on price/performance with >components available at the time it was designed. At the time the K1 was >designed, DDS units were not as available as today and were still quite >pricy - by the time the KX1 was designed, the cost of DDS had dropped >significantly. I would express a different view. I would hate to see the performance of the K1 *degraded* by the use of a DDS VFO. After experiencing how well the K1's LC VFO performs, I would now NOT buy a K1 if it used a DDS frequency generation scheme such as that found in the KX1 or DSW. A simple DDS VFO design such as is found in KX1 or DSW units puts a fair amount of spurious output directly into the higher level transmitter stages, and into the receiver mixer. This junk degrades transmitter spurious output quality and receiver performance. The K1's LC VFO and hetrodyne crystal oscillator output is far cleaner than any current DDS-only VFO. Those who wish for every little enhancement possible in the RF performance of a radio will NOT choose a simple DDS VFO design. More sophisticated rigs that use DDS use it in conjunction with a PLL to generate a much cleaner signal rather than using the direct raw output of a DDS chip. Perhaps soon a combo DDS-PLL chip that is low-cost and low-power will arrive for use in our QRP rigs and reduce the concern about spurious output. An additional issue arises from the requirement in the KX1 for the DDS to produce output frequencies over a very wide range as it changes band-to-band, mode-to-mode, and receive-to-transmit. The KX1 DDS generates all of the required frequencies directly, rather than through hetrodyning with crystal oscillators. The clocking rate for current low-cost low-power DDS chips like the KX1's AD9834 is limited to 50 MHz, and the maximum output frequency at that clock is about one-third of that (16.6 MHz). This means that coverage of any ham band above 20m is fundamentally out of the question. However, a simple DDS VFO has a few advantages over the LC VFO: Excellent stability, resetability, wide frequency span, and adaptibility to digital control. Only the first two are usually apparent to the operator. OTOH, the step-wise incremental tuning and the manipulations required to change the tuning step make DDS VFO tuning far less natural than that of the continuous output of an LC VFO that tunes where and just as fast or slow as I turn the dial. So the options are clear. Choose the simple DDS rig if crystal-like temperature stability and resetability are most important to you. Choose a LC VFO rig if overall RF performance and naturalness of tuning are most important to you. > I fail to understand how anyone could refer to this a > 'design problem'. Agreed. The *superior* performance of the LC VFO over the simple DDS VFO make it the choice of those for whom the RF signal performance of their radio is important. It's a very *positive* design feature of the K1 over the KX1 that may go unrecognized by those unfamiliar with the technical issues at hand. But returning back to the original question, I'd say that if anyone finds something simple that improves the already excellent stability of the K1 VFO, I'd certainly be interested in hearing about it. Happy experimenting! 73, Mike / KK5F _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
