Karl wrote: >The DDS chip with a TCXO frequency standard makes a really stable >radio. If Elecraft wanted to make an all band CW radio this design >might be the one to use.
The clock frequency of the DDS in the KX1 is 50 MHz, the highest for which the chip is rated. The highest usable output frequency from a DDS is about one-third of its DDS clock. You'll be out of luck trying to generate any transmit signal or receiver local oscillator signal above about 16.6 MHz. It seems to me that using a TXCO unit as the DDS clock would be gross overkill. The current design is already just about as stable as any simple crystal-controlled oscillator. It would be hard to justify the cost, size, and power consumption of the TXCO unit unless the radio is to be used for long sessions in frequency-critical data-mode operation, which the KX1 doesn't support for unrelated reasons. >The new Double Balanced Mixers can go a long way towards improving >Image rejection, a current problem with single conversion. The relatively high 4.9 MHz IF of the single conversion Elecraft rigs is already excellent for image rejection. Using a simple DDS frequency generating scheme, as opposed to a PLL locked to a DDS, is less than optimum for transmitter spurious output and for receiver performance, due to the DDS frequency spurs that always accompany the desired DDS frequency in the raw output. These are the main issues that degrade the RF performance of the KX1, compared to the K1 with its simple LC VFO and heterodyne crystal oscillator frequency generation scheme. 73, Mike / KK5F _______________________________________________ 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
