DFT Format: File Specification
652. The DFT drift data file consists of a variable number of 4 096 byte blocks, each block containing 8bit amplitudes and phases of the Doppler spectra. The smallest data entity is a subcase which contains a four Doppler spectrum for each antenna obtained at one frequency, one height gate, and one polarization setting. Each Doppler spectrum in a subcase is 2^{N} elements long, where N is selected by the operator. The amplitudes of individual Doppler spectra are grouped in sets of 128 elements for storage in the DFT file, each set of 128 amplitudes may contain data from one to four antennas depending on the setting of N. 128 amplitudes are followed by 128 phase values of the same Doppler spectrum or spectra.
653. The first byte of the first block in the DFT file is always forced to be a Record Type (0x0a). The structure shown by Table 614 on the next page illustrates the arrangement.
654. For one frequency a variable number of height gates may be selected. All subcases recorded for a single frequency comprise a Height Set and all those recorded simultaneously during one CIT are called a CIT Set. All subcases contained within one 4 096 block of drift data comprise a Case.
Table 614 DFT File Structure
Block 
Byte
Count 
Data
Description 
1 
1 
Record Type (0x0a
for Drift), 1 byte 

2128 
1st 128/2^{N}
* 8bit amplitude spectra (as logamplitudes in 3/8 dB units) with least
significant bit replaced by serially written header data 

129256 
128 8bit Phase
values of Doppler lines stored in previous 128 bytes 

2574096 
Repeat previous 256
bytes 15 more times. Order of spectra
is antenna 14, heights, frequencies, polarization 
2 
4096... 
Repeat 4 096 byte
blocks until end of data, placing 256 bytes of EE (hex) at end of data. If not end of a 4 096 byte block, then
zero fill 

* 
Where 2^{N}
is # of Doppler lines in the stored spectra 
655. The drift HEADER information is stored serially in the LSB of spectra amplitude bytes, LSB of the values first. The Header consists of Record Type (4 bits), Drift PREFACE (228 bits or, 57 4bit nibbles), and a variable number of subcase headers (52 bits, or 13 4bit nibbles, each ). This arrangement is illustrated in Table 615.
Table 615 Drift Header
Information Stored Serially in LSB of Amplitudes
Bit 
Description 
4 
Record type (0x0a
for Drift)  1 nibble 
228 
Drift Data PREFACE (57 nibbles) 
52 
Subcase Header
(Next 5 items in 13 nibbles): 

Actual Frequency in kHz (5 nibbles),
coded decimal 

Height in km of Maximum Amplitude Signal
for first Subcase (4 nibbles), coded decimal 

Height Bin Number of max amplitude (2
nibbles), binary 

Automatic Gain Offset 6 dB units of attenuation (in addition to
base gain), 1 nibble 

Polarization (X=0, O=1), 1 nibble 
52 
Repeat Subcase
Headers for all heights (1st freq and polarization), then store another group
of heights for all frequencies, then store another height/freq group for X
polarization (if selected) 
656. The Drift Data PREFACE structure is shown in Table 616. Each PREFACE value is a 4bit nibble and thus takes four bytes of the spectra amplitudes to be stored.
Table 616 Drift Data
Specification
Item # 
Description 
Units 
Range 
Accuracy 
Precision 
Type 
Format 
1,
2 
Year 
years 
099 
 
 
4bit BCD 
2 digits 
3,
4, 5 
Day of Year 
days 
1366 
 
 
4bit BCD 
4 digits 
6,
7 
Hour 
hours 
023 
 
 
4bit BCD 
2 digits 
8,
9 
Minute 
minutes 
059 
 
 
4bit BCD 
2 digits 
10,
11 
Second 
seconds 
059 
 
 
4bit BCD 
2 digits 
12 
Schedule # 
 
16 
 
 
4bit BCD 
1 digit 
13 
Program 
 
18 
 
 
4bit BCD 
1 digit 
14,
15 
Drift Data Flag 
 
FF (plain) 
FX codes comprise
DPS 
 
4bit hex 
 
16 
Journal, J 
bitencoded 
bit 0: new gain 
 
 
4bit hex 
binary 
17 
First height of
sampling window 
10 km 
0099 
10 km 
10 km 
4bit BCD 
2 digits 
18 
Height resolution 
encoded 
2  2.5 km 
2.5 km 
2.5 km 
4bit hex 
binary 
19 
Number of Heights 
encoded 
8  128 
 
 
4bit BCD 
binary 
20
 25 
Start Frequency 
100 Hz 
010000  450000 
1 kHz 
100 Hz 
4bit BCD 
6 digits 
26 
Disk IO 
 
Ah 
 
 
4bit hex 
binary 
27 
Frequency Search
Enabled 
 
0 (no) 
 
 
4bit BCD 
binary 
28.
29 
Fine Frequency Step 
10 kHz 
0255 
10 kHz 
10 kHz 
swapped 4bit nibbles
of 1 byte binary 
unsigned char 
30 
Number of small
steps in a scan, S, absolute value 
 
0 to 15 
 
 
4bit hex 
binary 
31,
32 
Number of small
steps in a scan, S 
 
15 to +15 
 
 
swapped 4bit nibbles
of 1 byte binary 
signed char 
33,
34 
Start Frequency, LL 
1 Mhz 
01 to 45 
1 MHz 
1 MHz 
4bit BCD 
2 digits 
35 
Coarse Frequency
Step, or number of repetitions 
encoded 
0 (200 kHz) 
 
 
4bit BCD 
binary 
36,
37 
Start Frequency, LL 
1 Mhz 
1 to 45 
1 MHz 
1 MHz 
4bit BCD 
2 digits 
38 
Bottom Height, B 
100 km 
0 to 15 
100 km 
100 km 
4bit hex 
binary 
39 
Top Height, T 
100 km 
0 to 15 
100 km 
100 km 
4bit hex 
binary 
40 
Unused 
 
 
 
 
 
 
41
 43 
Station ID 
 
000 to 999 
 
 
4bit BCD 
3 digits 
44 
Phase Code, X 
 
1 (complim.) 
 
 
4bit hex 
binary 
45 
Multiantenna
sequencing and O/X polarization options, A 
 
0 (sum), 
 
 
4bit hex 
binary 
46,
47 
CIT length 
sec 
0  255 
1 sec 
1 sec 
Two 4bit nibbles
of 1 byte binary 
unsigned char 
48 
Number of Doppler
lines, N 
encoded, actual
value is power of 2 
3  7 (power of 2) 
 
 
4bit BCD 
binary 
49 
Pulse Repetition
Rate, R 
encoded 
0 (50 pps) 
 
 
4bit BCD 
binary 
50 
Waveform, X 
 
1 (complim.) 
 
 
4bit hex 
binary 
51 
Delay, D 
50 msec 
0  15 
50 msec 
50 msec 
4bit hex 
binary 
52 
Frequency Search Offset 
 
0, 1, 2, 3, 4, E, F 
 
 
4bit hex 
binary 
53 
Auto Gain, G, offset 
6 dB 
0  15 
6 dB 
6 dB 
4bit hex 
binary 
54,
55 
Heights to Output, O 
 
0  255 
 
 
swapped 4bit nibbles
of 1 byte binary 
unsigned char 
56 
Number of polarizations 
 
1 or 2 
 
 
4bit BCD 
1 digit 
57 
Start Gain 
6 dB 
0  15 
 
 
4bit hex 
binary 