Toggle transmit data normal/invert
 A special demodulator for 300 Baud packet using an XR2211
 Help the CP-100 hear better

Toggle Transmitted Data Polarity Modification

Occasionally, you may come upon a RTTY station whom is transmitting in the wrong sideband or their software is accidentally set up to invert transmit data. If you make contact with this station you would have to change sidebands, or find the command in the program to invert, or you could do this mod, and flip a switch! The CP-100 has a normal and reverse button on it but that is just for receive only. That would work if the station is sending inverted but receiving normal. This doesn't happen often these days. The front panel of the CP-100 is pretty full and so you would have to see where you could fit the toggle switch and a L.E.D. if desired, on the front. I used a blinking L.E.D. to remind me that I am inverted during transmit. Traditionally, all digital communications are done in Lower Sideband. So why are these sound card programs upsetting tradition by using Upper Sideband by default? To date, I have not received a valid answer as to why.

A Special Demodulator Just for 300 Baud Packet

This design allows you to toggle between the CP-100 demodulator for RTTY, etc. and the XR-2211 tone decoder for for 300 baud packet demodulation. The CP-100 filtering is too narrow making for even slightly off frequency stations impossible to be decoded. Bypassing the filters and inserting the XR-2211 solves the problem and is able to track off frequency stations by approximately 30 Hertz either side of center tone frequency. This alone is well worth the modification as no one can seem to get on the same frequency! For the 'Lock L.E.D.', I recommend a L.E.D. with a clear lens. You can see the flicker better thus making it easier to tune with as opposed to a diffused (color) lens. When the L.E.D. stops flickering, it's locked on! Better yet, if you align the XR2211 to the same mark frequency as the CP-100 you can use the bargraph or Oscilloscope for tuning! The XR chip will need to be tuned up before use. For XR2211 alignment procedures, see the XR Chip page.

Oscilloscope Tuning for Superior Accuracy
	O' Scope tuning...It's the way to go! Any O' Scope will do. Connections for Mark and Space tones are output to the back of the CP-100. See CP-100 manual for connection details. If adding the XR2211 and you align the tone with the same tone the CP-100 uses then you will still be able to use the Oscilloscope for accurate tuning while the XR2211 is selected for demodulation.

Reducing the Amount of Audio Input Needed to CP-100

Have you noticed that it takes quite a lot of audio from your receiver to copy or to get all the tuning LED's lit up on the display? Adding an audio transformer that can be obtained from Radio Shack would be of great help to your CP-100. Lift the proper end of R1 off the board so that you can solder and install the transformer from the component side of the circuit board. I used shrink wrap to house my transformer and just hot glued it on top of the circuit board. After modification completion, you will definitely notice how you do not have to run your volume up so high that it blasts you out of the room anymore!

Technical Data

Download CP-100 instruction manual with schematic 1.86MB PDF

Download CP-100 bigger / better looking schematic 588K GIF

CP-100 main page

How to make TTL to RS-232 for the CP-100

XR2211 chip alignment procedure

Where to purchase the IC's

Notice...
You are encouraged to check all of the pages on this web site for the information you seek, starting at the main page. Each page is possibly related to another. The information on each page is "as-is", try at your own risk, and so on. We can help you out some what, as time permits. Try to stay on topic. Please, do not ask to "engineer" or "re-engineer" a design to suit your special project. We do not sell parts or kits of any kind. All said, we are open to any suggestions on adding more material, as long as it is on topic with a particular web page of the Technicothica web site. An example of things that are not "on topic" are: Support for APRS, EMWIN, TNC's and sound card stuff.    ~Thanks!

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