[Coco] COCO 3 for LowFER transmitter?

[John E. Malmberg]

Apparently this message never made it to the list until it was reposted 
here.
> -----Original Message----- 
> From: "Rev. James E. Smith" 
> Sent: Dec 7, 2003 2:14 AM 
> To: chaplainjones at earthlink.net 
> Subject: COCO 3 for LowFER transmitter? 
>  
> Dear Alan Jones,
> I have a COCO 3 that is still in great shape. I would like to know if I can
> use it as a LowFER home-brew beacon transmitter for operation at 160 to 190
> kHz 1750 meters? As to send Morse code, AM, and use it as a transmitter all
> in one. Since it has a output of Ch, 3 and Ch, 4 wide band how could I drop
> the frequency and narrow the bandwidth to less than 100 Hz without opening
> her up? I will be using FCC Part 15 rules. Any info you can send would be
> welcomed.

Converting the output from Channel 3 or Channel 4 to the VLF band would 
require external hardware, and you can not control the modulation, so 
all you would get out of it would be RFI or nothing depending on what 
you ended up with.

What you are asking on doing is converting two appoximately 65 Mhz 
signals, one AM and 3.5 Mhz wide and one FM about 15Khz wide to a single 
160 Mhz signal.

It is simply not practical to do.  And to even consider indicates that 
you are totally unaware of the relevant radio theory.

It may be possible to get the DAC that is used to provide audio output 
to cycle at between 160 and 190 Khz, but an external filter would still 
probably be needed.


Modulation internal to the COCO for AM, except for sounds is also 
limited, as the COCO only has a zero crossing detector for picking up audio.

The output of the COCO is a stair step function, and that can not be put 
directly on the air even if you can get it to generate the correct 
frequencies for CW or find a way to modulate it for AM.  It will 
generate too many harmonics, and thus violate part 15.

The external circuitry needed with any of these approaches basically 
ends up being the same complexity or even more complexity than if you 
just built a LowFER transmitter.

If you want to feed the output of a COCO DAC or Stereo Sound PAK to a 
real transmitter, then a filtering circuit is needed to supress the 
harmonics from the square waves.

-John
wb8tyw at qsl.net
Personal Opinion Only