Elecraft

A new KX1, maybe KX2?

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Karl Larsen

A new KX1, maybe KX2?

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 new Double Balanced Mixers can go a long way
towards improving Image rejection, a current problem with single conversion.

It would be a lot like the KX1 but I would want the transmit power
to be around 10 watts, it will cover all Ham bands from 160 through 10
meters. It will have a nice liquid crystal display of frequency and
other data. It will have VFO A and B. You can even build in a spot
function :-) but normal operation will move the transmitter a set
number of KHz up or down in frequency.

There are a number of nice CW features that can be built in and make
this the most frequency stable, most complete feature set CW radio kit
on the market.

73 Karl K5DI

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Mike Morrow-3

Re: A new KX1, maybe KX2?

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
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Karl Larsen

Re: A new KX1, maybe KX2?

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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>
>

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Geoffrey Mackenzie-Kennedy-2

Re: A new KX1, maybe KX2?

Karl Larsen wrote:

> There are new chips that run with a 100 MHz clock.

And things seem to be getting better. The Analog Devices AD9951 can I
understand be clocked at up to 400MHz, and I hear whispers about higher
clock frequencies.

>> 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.

Very true. Not much fun here looking down the throats of these monsters on
40m, most of whom use very big high gain antennas. The spurious responses
above 7.1MHz in my K2's receiver cause a big problem during the evenings.

> The latest mixers can help to stop this problem.

I'll second that, particularly in the case of the H-mode mixer.

73,
Geoff
GM4ESD

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Karl Larsen

Re: A new KX1, maybe KX2?

Geoffrey Mackenzie-Kennedy wrote:
> Karl Larsen wrote:
>
>> There are new chips that run with a 100 MHz clock.
>
> And things seem to be getting better. The Analog Devices AD9951 can I
> understand be clocked at up to 400MHz, and I hear whispers about
> higher clock frequencies.
Hi Geof, I get the Analog Devices newsletter but have been remiss in
reading it. But this assures we can clock the AD9951 at 100 MHz and then
generate the transmit signal, and receiver first mixer signal for a 160
to 10 meter transceiver.

>
>>> 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.
>
> Very true. Not much fun here looking down the throats of these
> monsters on 40m, most of whom use very big high gain antennas. The
> spurious responses above 7.1MHz in my K2's receiver cause a big
> problem during the evenings.
>
>> The latest mixers can help to stop this problem.
>
> I'll second that, particularly in the case of the H-mode mixer.
>

I have read about the new Mixers and to be honest I do not
understand the way they work. I'm 70 years old and my hobby is getting
complicated. I last looked at double balanced mixers which seemed to be
the best around.

Well I will place H-mode mixer in Google and see what comes up.

This all means that the KX1 can be improved into an all HF band
radio using the DDS tools now available. I think this change takes the
KX1 out of the battery operated small physical size to something a bit
larger. But maybe not too. It might be the same box as the KX1 but with
more controls.

73 Karl K5DI

> 73,
> Geoff
> GM4ESD
>
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