Hi!
Let me explain it a bit. In the WIki page for the DCS, they are stating, that from a total capacity of 512 DCS codes only 83 is available "to avoid falsing due to alignment collisions".
What does it mean ? I'll try to explain it by a very very simplified example:
Let's have a DCS system sending periodically triplets of digits in the range 0-2, i.e. there are the following combinations:
012 120 201 210 102 021.
How many combinations can you really use from these six ones ?
Just 2 (TWO). Why ?
Lets imagine you are sending the first combo. Periodically. So, the stream will be 012012012012012012....
And now let's try the second combo: 120120120120120120120120120....
And the third: 201201201201201201201201201.....
Looking in the middle of the stream, they are IDENTICAL! All contain the "basic" 012 sequence again and again.
It's very probable (almost sure) that the very beginning of the stream, which is the only what differs, will not be received, because the receiver circuits need some time to adapt to the received signal, set the proper gain etc... So, a few bits will be missing, and you have to sync from the middle of the stream. And you can't do it, because all the streams are the same.
Similarly, the remaining three combinations produce identical stream, but different from the first one: 210210210210210210210210...
Do you see ? There isn't a typical fragment of "012" frtom the stream, but there is "210" instead.
Fine. And now: You have two radio manufacturers. One of them is serious and tells you: Our radios offer 2 DCS codes: 012 and 210.
And the other tells you: We have 2 standard DCS codes and 4 non-standard! What's better ?
An example of such a sh***y radios are Anytone AT-D878UV and similar models. There is no check of the entered DCS code, so you can enter anything from 000 to 777! And it's extremely stupid. Because I understand what's really happening, I would like to use a recommended code to prevent colliding with other codes. And it's not even possible! I have to take a table of regular DCS codes to seek for one! So, thanks to the developers of OpenGD77 for making extra effort to implement this table to the radio for me. To be honest, I didn't look to the sources if it's really there, it's possible that it's in the chipset and you send just a DCS code index when programming it for TX/RX, I don't know. Feel free to look to the public source code, modify it and recompile for your own pleasure
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With regards / 73,
OK1PT Pavel