Re: A simple 60 meter CW transmitter


Don Wilhelm <w3fpr@...>
 

Bill,

No I don't have information to refute the phase noise situation.  My thoughts are that at QRP levels, the problem is not as severe and may be able to be ignored.  At higher power levels, it is definitely a problem on the bands.
What I do know is that all DDS units are not the same, some are worse for phase noise than others.

IMHO, if the design point is for small, QRP and portable, the DDS solution is viable, or something like the SI570.  The nice part about that approach is that the generator can be easily offset for CW receive so it can be used not only as the transmit VFO, but also changed to be the LO source for a superhet receiver.  It is a small matter of programming.  It also makes multiband capability possible in a smaller package.  How about an 80, 60 (channelized), and 40 meter SSB and CW transceiver the size of an Elecraft K1.

Once one accepts the fact that properly designed firmware can be used, the possibilities of a small display (like the 3 digit LED display on the Elecraft KX1) is not only possible, but can add a lot of function to a small package.
OTOH, that may be too ambitious for a 4SQRP kit if the programming skills are not available to make that happen.

73,
Don W3FPR

On 6/15/2015 12:30 PM, Bill Cromwell wrcromwell@... [4sqrp] wrote:
 

Hi Don,

It's the close in phase noise that concerned me Some hams (and
engineers) have shown that it doesn't get filtered out. Apparently you
have to also filter out the desired signal to get the phase noise. Do
you have information that refutes this? It's easy to find misinformation
*everywhere* and maybe the best I have is wrong.

I would otherwise be happy to have something like that for my carrier
generator and heterodyne channel oscillators. My notion of seven xtals
(or available oscillator frequencies) is to allow for SSB *AND* CW in
one transmitter. That is one heterodyne frequency per channel (5) and
one each for either CW or SSB (2). Still five channels with a simple
selector.

73,

Bill KU8H

On 06/15/2015 11:11 AM, Don Wilhelm wrote:
> Bill,
>
> Following a DDS with a low pass filter will take care of most of the
> crud and the low pass filter on the PA will take care of the rest of it.
> I have looked at the spectrum of the Elecraft KX1 and the output is
> clean even though the source is a DDS.
>
> With the right firmware, I think the KX1 could easily be put on 60
> meters, but that firmware is Elecraft proprietary.
>
> 73,
> Don W3FPR
>
> On 6/15/2015 9:52 AM, Bill Cromwell wrcromwell@... [4sqrp] wrote:
>>
>> Hi Nick,
>>
>> If we want "simple" LEDs would be overly complex and expensive. A
>> chicken-head knob can point at dymo label or sharpie numbers one through
>> five on the front panel..assuming we actually use a front panel.
>>
>> I have been avoiding the DDS type stuff to also avoid the transmitted
>> crud that goes along with them.
>>
>> 73,
>>
>> Bill KU8H
>>
>


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