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Author Topic: RTTY protocol help  (Read 841 times)

Offline Zazzle

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RTTY protocol help
« on: September 29, 2017, 1034 UTC »
Heyho.

Gonna write a RTTY Encoder in Perl. I read some documentation but like to ask for some checks and advice whether I understood the stuff properly.

RTTY uses CCITT-2, yes?

It's 5 Bits but for practial use it's 8 bits, yes? (2x Startbit, 5x Code-Bits, 1x Stopbit)

Start- and Stopbit always  red "1", yes?

So, sending "A" is "11 00011 1"?

Switch between the NUMBER and ALPHABET blocks is done by it's own command (and not combined with space)? So I send <^letters> <flag or block switch> <bumbers> <Flag or block switch> <letters> (...)

Is there something like a Frame marker, a head/endblock or something?

Some advice on timing between blocks/transmissions?

Could someone provide me with an example? :)

Kind greetings,
Zazzle
Trans-/Receivers: JRC NRD-525,  ICOM IC-R72,  YAESU VR-5000,  YAESU FT-897D
Antennas: 80M Halfwave Dipole,  40m Inverted-V,  5/8λ Groundplane,  20M Longwire,  misc. UHF/VHF Scanner Antennas.

Offline ChrisSmolinski

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Re: RTTY protocol help
« Reply #1 on: September 29, 2017, 1109 UTC »
RTTY (FSK) uses a logical 0 for the start bit, and a 1 for the stop bit.

Baudot is a 5 bit code, ASCII can be sent at either 7 or 8 bits and there can be a parity bit when it is 7 bits of data (optional).

The switching between numeric and alphabet is only done in the 5 bit baudot mode, and is done as necessary.

No frame markers or anything like that. Very simple. 

Unfortunately RTTY is not very robust. PSK31 would be more robust, but obviously more difficult to transmit.

Have you looked into Hellschreiber ?  Since it is copied by looking at the resulting image and the decoding is done in the brain, it is fairly robust even under noisy conditions. Plus is it is a fun and under-utilized mode  ;D
Chris Smolinski
Westminster, MD
eQSLs appreciated! Send to: csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Zazzle

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Re: RTTY protocol help
« Reply #2 on: September 29, 2017, 1409 UTC »
Heyho!

First: thanks for the fast answer! :)

I'm basically aiming for the standard type of code with is most common/classic. I know there's variations that use plain 7/8 Bit ASCII straight from the table.

RTTY (FSK) uses a logical 0 for the start bit, and a 1 for the stop bit.
Baudot is a 5 bit code, ASCII can be sent at either 7 or 8 bits and there can be a parity bit when it is 7 bits of data (optional).
The switching between numeric and alphabet is only done in the 5 bit baudot mode, and is done as necessary.
No frame markers or anything like that. Very simple. 

So it works like this?
Code: [Select]
(optional leading RYRYRYRYRY)
[1][Letter][0]
[1][Letter][0]
[1][Letter][0]
[1][Letter][0]
[1][Switch to numbers][0]
[1][Number][0]
[1][Number][0]
[1][Number][0]
[1][Switch to letters][0]
[1][Letter][0]
(...)

Unfortunately RTTY is not very robust. PSK31 would be more robust, but obviously more difficult to transmitt.
Have you looked into Hellschreiber?  Since it is copied by looking at the resulting image and the decoding is done in the brain, it is fairly robust even under noisy conditions. Plus is it is a fun and under-utilized mode  ;D

Yea, it requires a higher bandwidth and is therefore more prone to be affected by noise. Sicne I'm almost done with the TX setup... too lazy to rip it apart for PSK31. ^^'
Hell is fun. But actually it requires a waterfall monitor. I wanna make sure it can be decoded by as many people as possible. And CW ist most straight forward, with RTTY the next common.

I'm not entirely sure myself whether I stick to CW with a higher rate or change to RTTY. Since I'll use at Raspi... I can just change it with a few commands :)

I also learned, which confused me before, that the RYRYRYRYRY stuff at the beginning is legacy stuff to sync the baudrate.

Kind greetings,
~Zazzle
Trans-/Receivers: JRC NRD-525,  ICOM IC-R72,  YAESU VR-5000,  YAESU FT-897D
Antennas: 80M Halfwave Dipole,  40m Inverted-V,  5/8λ Groundplane,  20M Longwire,  misc. UHF/VHF Scanner Antennas.

Offline ChrisSmolinski

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Re: RTTY protocol help
« Reply #3 on: September 29, 2017, 1418 UTC »
If you are using a CPU, you could always send a mix of modes, CW, RTTY, and Hell. That would allow everyone to listen, plus you could learn what modes work best under different conditions?
Chris Smolinski
Westminster, MD
eQSLs appreciated! Send to: csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Zazzle

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Re: RTTY protocol help
« Reply #4 on: September 29, 2017, 1505 UTC »
Hey Chris!

If you are using a CPU, you could always send a mix of modes, CW, RTTY, and Hell. That would allow everyone to listen, plus you could learn what modes work best under different conditions?

Stop giving me Ideas! :D

Actually, I could do a switch between RTTY and CW. Can add that without big hassle.
Maybe I'm going to add Hellschreiber later.

Kind greetings,
Zazzle.
Trans-/Receivers: JRC NRD-525,  ICOM IC-R72,  YAESU VR-5000,  YAESU FT-897D
Antennas: 80M Halfwave Dipole,  40m Inverted-V,  5/8λ Groundplane,  20M Longwire,  misc. UHF/VHF Scanner Antennas.

Offline Josh

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Re: RTTY protocol help
« Reply #5 on: September 29, 2017, 1552 UTC »
Oooo! OOOOOoo do a binary coded decimal system like what wwv uses!

Offline Zazzle

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Re: RTTY protocol help
« Reply #6 on: September 30, 2017, 0901 UTC »
Oooo! OOOOOoo do a binary coded decimal system like what wwv uses!


Noooooooooooooooooo! :D
Trans-/Receivers: JRC NRD-525,  ICOM IC-R72,  YAESU VR-5000,  YAESU FT-897D
Antennas: 80M Halfwave Dipole,  40m Inverted-V,  5/8λ Groundplane,  20M Longwire,  misc. UHF/VHF Scanner Antennas.