[ACARS] Help with HFDL

[Mike L]

John McKay wrote:
> 
>   I have been trying the demo version of PC-HFDL but keep getting error
> messages like those below.
> What am I doing wrong?
> 
> Preamble 300  bps 1.8 sec Interleaver FREQ ERR -43.947634 Hz Errors 13
> Preamble 300  bps 1.8 sec Interleaver FREQ ERR -44.327738 Hz Errors 97

Hi John, & All
You're doing nothing wrong.
The algo's used by Charles Brain for the PC-HFDL prog are very precise, all this is 
saying is that you are tuned slightly too high and that there is some "crap" on the 
signal, if your errors were positive then your tuned on the low side.
By very careful tuning of the received sig you can get the FREQ ERR down to about 
0.30000000 Hz, BUT this will only be temporary as propo variations will swing it 
around by about +-50Hz of nominal, distances are large with HFDL.
The number of errors can be quite high even for a "perfect" decode.

Cheers
Mike L