Re: A simple 60 meter CW transmitter


Don Wilhelm <w3fpr@...>
 

Nick,

I have built plenty of DC receivers and have been disappointed by each of them.  Apologies to the DC receiver fans, but I like single signal receive and do not like the potential microphonics that some DC receivers produce.  I have tried them, and will trade the DC receiver for a superhet any day.  A good DC receiver may exist, but it takes great care in design and construction.  IMHO, those are "play" receivers and are not for any serious work.

A receiver that makes the top of the Sherwood listing would be 'overkill', but something with decent selectivity, image rejection, and reasonable sensitivity is in order for anything that can properly call itself a receiver in today's bands is a requirement IMHO.  Yes, that includes a receiver that will stand up in contest situations with QRO stations all around (good Dynamic Range), and adequate selectivity to separate stations in a pileup situation.

OK, all of that may not be applicable to operation on channelized 60 meters, but is my bottom-line requirement for a receiver.

73,
Don W3FPR

On 6/15/2015 7:28 PM, 'Nick Kennedy' nick-wa5bdu@... [4sqrp] wrote:
 

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 monitoring.
 


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