Getting an old RTTY demodulator to work

Just bought a second hand Code master CWR-610E telereader, which can decode rtty (and CW) and display it on a compositie video screen. Amazingly for a early 80’s device it worked perfectly.

The code master CWR-610E in all its naked glory

I do had to do some adjustements, but they were all outlined in the excellent manual.

The first thing I did was changing the video output to composite instead of RF. This meant changing the following things:

Changing method when using video monitor TV instead of home TV (RF)

Changing from RF OUT to VIDEO OUT

Cut and bridge with solder at two positions:
1. RF OUT selector part: Cut "R" - short "V".
2. RF converter part: Cut "RF -VIO".

Cut and short correctly by referring to the parts layout chart.

VIDEO OUT specification
Composite video signals (video normal modulation, synchronous negative modulation, 1.0 ± 0.2 Vp-p, 75 ohms).

This gave a beautiful, steady image on the small b/w monitor I have:

Composite output!

Next: getting signal into it.

Since my transceiver isn’t connected yet, I connected my smartphone’s output and lo and behold, the signal came trough, but was gibberish.

After some research, I found out that the weather rtty I was trying to decode, was in reverse coding, so I had to set that up.

That involved cutting a trace on the board:

The input of Baudot and ASCII is set at mark L at the time of shipping. It can be changed to mark H.

Cut the MODE SEL REV [cut land REV].

After that and setting the baudot rate to 50bps it worked!

Finally some legible text. not perfect though.

Once my transceiver is set up, I will try and make it better and make some RTTY QSO’s.

Next time I will try to add a switch to switch between normal and reverse.