Toggle transmit data normal/invert
 Enabling 300 baud (packet) operation
 A special demodulator for 300 Baud packet using an XR2211
 Reducing the amount of audio input needed to CP-1

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-1 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. For placement of the switch and L.E.D. take a look at the bottom of this page at a picture of my CP-1. 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.

Enable 300 Baud Operation for Packet

This information can also be found on page 7 in the AEA CP-1 manual. However there is no mention of toggling between widening the low pass filter and returning it to normal. The diagram shown below allows you to make the selection. Even after the modification, tuning can be a bit touchy. There is a picture towards the bottom of this page that shows where I placed the switches and L.E.D.'s for several modifications on the front of my CP-1. If you are a serious packet user, you may want to skip this mod and see the modification using an XR-2211 tone decoder IC for packet. Bypassing the CP-1 filtering and using the XR2211 IC as a demodulator works much better for packet reception. The XR2211 can track off frequency stations by 30Hz either side of center tone frequency. You bet I installed one in mine!

A Special Demodulator Just for 300 Baud Packet

This design allows you to toggle between the CP-1 demodulator for RTTY, etc. and the XR-2211 tone decoder for for 300 baud packet demodulation. The CP-1 filtering is too narrow making for even slightly off frequency stations impossible to be decoded. Actually the CP-1 was not designed for packet. 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! Or better yet, align the mark tone of the XR221 with the mark tone in the CP-1 so 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-1manual for connection details. If you carefully align the XR2211 with the same tone the CP-1 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-1

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-1. Lift the proper end of R2 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!

KC4KLM's CP-1 with all the Switches and L.E.D.'s Added
From left to right: The white switch and clear L.E.D. toggle CP-1 and XR2211 demodulation. I prefer a non-diffused L.E.D. in this application because it is easier to see the 'flicker' for tuning purposes. The yellow switch and yellow L.E.D. opens up the low pass filter a bit to allow 300 Baud operation. This is now obsolete on my CP-1 since I have added the XR2211.	The red switch and red blinking L.E.D. toggles between transmit data normal or invert. The blinking LED reminds me to return the data transmit to 'normal' after I have finished my upside down QSO.

Technical Data

Download CP-1 instruction manual with schematic 2.125MB PDF

Download XR2211 tone decoder data sheets

Where to purchase the IC's

AEA CP-1 main page

RS-232 interface for the AEA CP-1

How to make other TTL to RS-232 interfaces

DOS programs for the AEA-CP-1

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!