[Elecraft] A new KX1, maybe KX2?

[Karl Larsen]

Mike Morrow wrote:
> 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. 
    There are new chips that run with a 100 MHz clock.
>  The highest usable output frequency from a DDS is about one-third of its DDS clock. 
    Exactly right Mike.
>   You'll be out of luck trying to generate any transmit signal or receiver local oscillator signal above about 16.6 MHz.
>   
    Not a problem doing so if we either use the faster DDS Chip and 
TCXO. I think the new DDS uses much more current, as expected, and if 
not good then consider using a simple doubler circuit for obtaining 
17,15,24, and 10 meters.
> 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.  
>   
    This off the wall  KX2 is not a simple radio. It should be complex 
and have all the features you have on the expensive radios at a lower 
cost. The TXCO is cheap, like $5.00 for a 75 MHz job and it's 1/2 by 1/4 
inch solid copper. I have one in my ATS-3 kit radio.
>   
>> 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.
>
>   
    Not so. Ask any European user and they will talk about Broadcast 
spurs that occur when a 350,000 Watt station is 1 hop away on the Image 
frequency. The latest mixers can help to stop this problem.
> 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.
>   
    There are some spurs from the Digital part of the DDS and you must 
be smart to filter them out. This can be done and is done in the KX1.
> 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.
>   
    The K2 is about 1992 technology. It will work fine but I expect the 
KX2 to be superior.
> 73,
> Mike / KK5F
>   

73 Karl K5DI

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