Dear Bill, Paul G4WPA and George WB5JJJ
Solved.
Thank you Bill for reminding me about endianness and Paul for explaining that
0,0,0,0,0,0,0,0 is indeed zero.
The solution was actually quite simple :- reverse the byte order of the eight
bytes starting at the 32nd byte and then use .Net BitConverter.ToDouble.
My mistake was that I tried to make sense of the byte array pattern rather than
use program functions. I am still wondering why there is a ninth byte and must
presume that the equalness of the 33rd and 34th byte is some arithmetic
artifact.
Thank you Bill for reminding me also of assuming fixed positions in the byte
array. I had assumed that the ID (unique key) was always "WSJT-X" but you have
pointed out that this field reflects command line parameters so I am duly
warned.
Now some background for George WB5JJJ.
I am using Dimension 4 as a service to synchronise my PC clock every nine
minutes. However when I scan the DT column in the Band Activity window it seems
that there are always more positives than negatives. When I look at the history
window in Dimension 4 the situation is the same. I don't know why.
The average advance is about 0.2 seconds.but this may occasionally reach 0.5
seconds before synchronisation is triggered. This was not a big deal for me
until FT4 arrived where the timing is more critical.
I particularly want to know if my time error is affecting my FT4 decodes so I
want a histogram or a moving average. Nudging based on a 'follow the herd'
principle does not seem like a bad idea to me. 73 de G4SWY Derek +++
On Tuesday, 14 May 2019, 22:54:28 BST, Bill Somerville
<[email protected]> wrote:
On 14/05/2019 22:26, Derek Turner via wsjt-devel wrote:
So I know I am looking in the right place, which is the eight bytes starting
at (zero base) byte 32 . Here is a screen shot from an Excel worksheet where I
compare samples of the Band Activity DT with their Decode byte array bytes:-
I have several issues here that I do not understand :-
1. The pattern of bytes for negative and positive Delta Times are identical
so the sign is lost. 2. Between SNR and Delta Frequency there are nine bytes,
not the eight I expected for a Double. Byte 40 appears to be surplus. 3. DT 0
is suspiciously all zeros when DT 0.1 seems to be a very large number. 4. Bytes
33 and 34 are identical.
Please can somebody make sense of this for me.
Hi Derek,
beware of assuming fixed start positions for fields in the messages, if there
are preceding string fields then the following fields will be moved according
the length of the string field(s). You will be ok in this case so long as you
always start WSJT-X with the same command line parameters.
The main issue is that you are not allowing for the fields in the message being
stored in network byte order, i.e. Big Endian. If you are receiving on a little
Endian architecture then you must swap the bytes of any numeric fields longer
than one byte.
73
Bill
G4WJS.
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