Here is an analysis of the contents of the pchfdl.dat file.
Using HxD Hexeditor version 1.7.7.0 freeware
https://mh-nexus.de/en/hxd/the first 16 bytes of the pchfdl.dat file for system table 49 are
05 00 00 00 04 00 00 00 31 00 00 00 0F 00 00 00
31 hexadecimal = 49 decimal
This is followed by the information for ground station 1
01 00 00 00 00 00 00 00 A5 96 0A 00 AE B4 01 00
08 00 00 00 00 00 00 00 B0 AF 4E 01 04 00 00 00
18 6C 11 01 0C 00 00 00 60 93 CA 00 08 00 00 00
18 D6 AC 00 04 00 00 00 E8 D2 99 00 04 00 00 00
18 37 88 00 0C 00 00 00 18 15 64 00 08 00 00 00
A0 0B 54 00 04 00 00 00 00 00 00 00 00 00 00 00
The 01 is for ground station 1
The bytes A5 96 0A are LSB.MSB for the ground station longitude.
The bytes AE B4 01 are LSB.MSB for the ground station latitude.
These are 20-bit signed integers using two's complement notation
with 180 degrees equal to 7FFFF (524287 01111111111111111111)
and with North and East as positive numbers.
If bit 20 is a 1 then the number is negative
and in two's complement notation.
0A96A5 = 693925 = 10101001011010100101
Two's complement 01010110100101011011 = -05695B = -354651
-354651 * 180/524287 = -121.76 121 45' 34" W = -121.76 degrees
01B4AE = 111790 = 00011011010010101110
111790 * 180/524287 = 38.38 38 22' 48" N = 38.38 degrees
The 08 denotes 8 frequencies.
The bytes B0 AF 4E 01 04 are LSB..MSB for frequency and 04 for Slot 4
014EAFB0 = 21934000
The bytes 18 6C 11 01 0C are LSB..MSB for frequency and 0C for Slot 12
01116C18 = 17919000
The bytes 60 93 CA 00 08 are LSB..MSB for frequency and 08 for Slot 8
00CA9360 = 13276000
The bytes 18 D6 AC 00 04 are LSB..MSB for frequency and 04 for Slot 4
00ACD618 = 11327000
The bytes E8 D2 99 00 04 are LSB..MSB for frequency and 04 for Slot 4
0099D2E8 = 10081000
The bytes 18 37 88 00 0C are LSB..MSB for frequency and 0C for Slot 12
00883718 = 8927000
The bytes 18 15 64 00 08 are LSB..MSB for frequency and 08 for Slot 8
00641518 = 6559000
The bytes A0 0B 54 00 04 are LSB..MSB for frequency and 04 for Slot 4
00540BA0 = 5508000
Ground Station ID 1 SAN FRANCISCO - CALIFORNIA
Longitude 121 45 34 W Latitude 38 22 48 N
Number of frequencies 8
Frequency 21934000 Hz Master Frame Slot 4
Frequency 17919000 Hz Master Frame Slot 12
Frequency 13276000 Hz Master Frame Slot 8
Frequency 11327000 Hz Master Frame Slot 4
Frequency 10081000 Hz Master Frame Slot 4
Frequency 8927000 Hz Master Frame Slot 12
Frequency 6559000 Hz Master Frame Slot 8
Frequency 5508000 Hz Master Frame Slot 4
Some additional detailed technical information for the HF data link (HFDL) system
can be found at the following website.
http://www.icao.int/safety/acp/inactive%20working%20groups%20library/amcp%205/item-1c.pdfTwo's Complement to Decimal converter can be found at
http://www.exploringbinary.com/twos-complement-converter/http://www.convertforfree.com/twos-complement-calculator/http://www.hobbyprojects.com/calculators/binary_decimal_hex_converter.html