[Coco] COCO 3 for LowFER transmitter?

[jdaggett at gate.net]

On 10 Dec 2003 at 13:56, KnudsenMJ at aol.com wrote:

> In a message dated 12/10/03 11:22:26 AM Eastern Standard Time, 
> jdaggett at gate.net writes:
> 
> > All the software has to do is to control the DAC and when to turn it
> > on and off to the 
> >  Morse code being sent. 
> 
> Use the cassette relay to key the CW carrier.  If you run the carrier
> continuous and key the audio via the DAC, you'll be output MCW, which
> I believe the FCC has banned from every band (marine and Ham) for a
> long time, as a waste of spectrum space. Though the Lowfer band rules
> are probably different.
> 
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FOrm a quick look that  band seems to have less restriction on the use of te 
spectrum than Amature. I have not used CW since 1976 so I really do not keep up 
with the rules. MCM is still permitted above 50 MHz. It seems that the allow double 
sideband full carrier and not tone modualted carrier. Same bandwidth. Unless they 
killed DSB AM full carrier on the 80 meter band. 

Still it is an easier circuit. More like using a 16 lbs sledge to kill an ant though. 

use the E or an XOR of the E and Q clocks and feed that into a programable 
divider. The output from the divider feeds one input of a two input and gate. The 
other input goes to one of the unused pins of IC4. That is used to turn the carrier on 
and off. The output of the and gate feeds a lowpass filter and to the power 
trransistor. 

That way you do not have the relay clicking so much. It will eventually wear out. 

> As someone else mentioned, there are BASIC ROM functions to generate
> sine waves of two freqs -- 1200 and 2400 Hz, IIRC.  There is a nice
> sine wave table in the ROMs somewhere -- 16 samples, I think.  You
> could build a better one with 256 samples, and not have to filter the
> DAC audio output as hard, though audio filtering is easy with an op
> amp and a couple Rs and Cs.  I built some hardware to generate PL tone
> for a 2m repeater that way once, though not using a Coco. --Mike K.
> 
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Yes the samples are poor as you only have a 6 bit DAC. A post filter is not that 
much to do. Dual opamps are cheap. In fact a simple two stage RC filter may work. 
There may even be a cheap audio DDS chip floating on the market. 


james


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