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Sounds like a design idea to me!
When do we get to see the prototype??
On Monday, June 15, 2015, 'Nick Kennedy' nick-wa5bdu@...
I think the output of a typical DDS is reasonably clean. If the
object is to make a receiver that tops Bob Sherwood’s list, some extra pains
might be required.
No, phase noise can’t be filtered. I think with a DDS it’s related to
jitter on the reference and with a PLL/VCO, it’s due to “hunting” by the
feedback loop which causes a small amount of FMing. I’m not sure any
frequency source can be completely free of phase noise.
A DDS can usually be had for less than $10.00 and Arduino Nanos can be
gotten 3 for $10 postpaid these days. It’s hard to justify a bare MCU chip
at those prices.
As far as channel indication goes, with enough pins you would have
plenty to do an LED per channel, but yeah there are surely better ways.
Looking at my old project, I think I used a piezo beeper to announce the channel
in Morse. But if you want to get fancy, nice backlit white on blue 2x16
LCD displays can be had for $1.89 each, postpaid. Amazing. You could also
use three LEDs in a binary weighted scheme ...
There are several other advantages associated with having your LO / VFO
under software control. You could implement RIT – not that the other guy
might be off frequency, but so you can adjust his pitch to your liking.
And if you choose to have a superhet receiver instead of direct conversion, it’s
easy to do the offset for the IF frequency. And that’s not all (sounding
like a TV pitch man now ...) you could toggle between the right LO frequency to
receive CW or switch to the right frequency for decoding USB in the
channel. That would make cross-mode QSOs possible and possibly make it a
bit easier to make sure the channel isn’t in use before calling. Or just for
Fun stuff ...
Sent: Monday, June 15, 2015 12:38 PM
Subject: Re: [4sqrp] A simple 60 meter CW
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
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
OTOH, that may be too ambitious for a 4SQRP kit if the programming
skills are not available to make that happen.
It's the close in phase noise that concerned me Some hams
engineers) have shown that it doesn't get filtered out. Apparently
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
heterodyne channel oscillators. My notion of seven xtals
oscillator frequencies) is to allow for SSB *AND* CW in
That is one heterodyne frequency per channel (5) and
one each for either
CW or SSB (2). Still five channels with a simple
On 06/15/2015 11:11 AM, Don
> 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
> With the right firmware, I think the KX1 could easily
be put on 60
> meters, but that firmware is Elecraft
> Don W3FPR
6/15/2015 9:52 AM, Bill Cromwell wrcromwell@... [4sqrp]
>> 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
>> five on the front panel..assuming we actually use a front
>> I have been avoiding the DDS type stuff to also
avoid the transmitted
>> crud that goes along with
QRP....."More smiles per Watt"
JOHNNY AC0BQ ..