[RESEND] Re: [Coco] COCO 3 for LowFER transmitter?

[Dennis Bathory-Kitsz]

Considering that the original request was to see if a Coco3 could be used
for a 
Lowfer beacon I suggests a frequency derived off the E clock. I did alss
mention it 
was like using a 16lb sledge to kill an ant. A bit to much. 

Correct in that a pure CW signal is better than an amplitude modulated
carrier is for 
reception. The narrow bandwidth requirements of a receiver for slow on off CW 
carrier will reflect in lower noise power density within the bandpass.
Another 
problem is the atmospheric noise power. At those frequencies trtrying to
hear a 
signal in all that noise from manmade and atmospheric sources is a
challenge even 
with low speed CW. Also at that frequency and that low a power I would
recommend 
a tuned loop antenna for transmitting. It will meet the requirements. The
efficiency 
can be made quite high. Much higher than any loaded vertical. 


james


On 10 Dec 2003 at 22:25, John E. Malmberg wrote:

> jdaggett at gate.net wrote:
> > 
> > The neatest way to get the carier frequency needed is to divide the
> > E clock freqency with an external divider. 
> 
> Which of course is wasteful, as it is cheaper and easier to use a
> clock source independant of the COCO.
> 
> Direct digital systhesis may be an option now for that.
> 
> > There are routines in the cassette output section of the basic roms
> > that will generate the audio to modulate the carrier. 
> > 
> > To store data on the cassette the Coco outputs AFSK baseband signal.
> > I am not sure if AFSK is permitted on that segment. 
> 
> I think it is as long as it fits in the bandwidth and the power 
> restrictions it is ok.
> 
> The power and antenna restrictions would have me persue more creative
> methods of building the transmitter.  There is no restriction on the
> length of the control lines.
> 
> My previous LowFER which only existed on a breadboard was a
> transverter.
> 
> I used a 3.58 Mhz crystal and a Yaesu FT101B to drive it.  I could
> transmit on SSB, CW, or AM.  By moving the correction dial on the
> Yaesu 79 Khz over, I had exact tuning.
> 
> 
> -John
> wb8tyw at qsl.net
> Personal Opinion Only
> 
> 
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