RTTY to telex

#1

Dear forum members!

After some pretty long time, I finally have some time(or at least I hope that I will have) to look into this hobby again. My interest this time is printing the DWD weather forecast messages on a telex machine. I have access to a shortwave radio to receive the signal and get it out of the radio, however I ran into some obstacles to feed it to the machine.

So far I tried the following things:

I have access to a Dovetron MCP-1000/T RTTY demodulator. While the cross indicator and the loop led works and indicate some decoding, I did not managed to get any data out of it. Might be defective, or might be a wrong wiring issue.

I also have a Pakratt 232 multi protocol modem (Model PK-232MBX). This device works fine, and I was able to set it up to decode the weather transmission and output it on the serial port. But then I'm a bit lost on the direction to feed this RS-232 signal into the i-Telex system

What would be your recommendation?

Obtain some dedicated RTTY decoder for telex devices? If yes, do you have a particular device in mind?

Build a custom microcontroller device reading the RS232 stream and translate/inject it to the TWI interface of the i-Telex system?

Something else?

Any suggestion more than welcome!

Best regard,
Balazs

#2

Hi Balazs,

So, both of the converters you have are RS232 output - these will not drive a Telex directly.

There are designs on the internet that convert from RS232 to current loop - a little construction work and this might just solve the problem.

Easiest way, assuming your machines have TW39 style interface will be to try to find a Minix MSK10b Konverter - feed audio in and get 40mA current loop out.

What are you planning to use to listing to DWD? the RFT EKD300 already has an interface to allow the radio to connect directly to a Telex...

Regards from England
Sean
M1ECY

#3

I think the Dovetron might be putting out a 60ma loop, so you may need a resistor in the loop. Dovetrons are notoriously off frequency. You can’t trust the dial. But if you are using the crosshairs and aligning it, it could be other issues causing your problem. I’ve not had much luck with Dovetrons in the long run.

#4

If it it the T Model (Tempest) then it provided RS232 and +/-6V according to the manuals.

They do seem quite fussy - I must find one

#5

Aha. I’ve never seen that model. Thanks for the info, Sean.

#6

I have one of these "tempest" models and built a simple RS232 to loop converter out of a few components to
operate it with a line current machine.

#7

Dear all,

Thanks for the answers and the suggestions. I think the first item should be the RS232-40mA converter - seems to be quite easy to do. Or maybe I will create something to convert the RS232 to the iTelex TWI protocol (I'm more familiar with microcontroller programming than electronics)

I would like to learn more about the EKD300 solution. I saw that it has a current loop output, but does that mean it also provide the 60V working voltage, or that should be provided externally? I have an EKD300 but it's defective - not turning on at all. I might have somebody in the country who could fix it, just pretty far away. Logistics....

Minix MSK10b - thanks for the suggestions Sean, I will try to find one.

Regarding the purpose of this whole exercise: we have regular exhibitions with my HAM radio club. Mostly it's focusing on military radios, but I sometimes bring my telexes with me, and exhibit it. This year I want to showcase something new, printing weather info seems to be interesting enough. The real ace thing would be printing weather fax

Balazs

#8

Yes, the EKD300 receiver has a basic RTTY Terminal unit that provides all the loop current and voltage to drive the Telex machine.