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
_______________________________________________
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
_______________________________________________
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
