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Overview
The HF-APRS beacon has been redesigned. It is an index card size (3" x 5") 4-layer board. It can generate a PSK-31 or most any other digital mode from DC - 70MHz. Although we are limited practically by half-octave output filters. The initial plan is to provide support for 3.5 / 14MHz for night / day coverage. Power output is 33dBm (2 watts). There is also a VHF 144-148MHz channel good for 27dBm (500mW). We'll run A-FSK APRS on 144.39 for a flight and perhaps 9600 baud FSK for faster telemetry updates. The board has a built in GPS, data logger, temp/hum sensor, output to control a ballast pump and cut down, and power converters. It will run on 9-20VDC. The whole thing will fit in a Size 1120 Pelican case and should weigh around 2 pounds with batteries. (24x L91s). That will give us a little over 100WH of prime power.
Transmit Schedule
Shown below is the transmit schedule. Time slotting is a system where the transmit frequency is selected based on
the current time. For example, 16:01:00 UTC
a PSK-31 message will be transmitted on 14070.450KHz and 1200 baud, A-FSK APRS packets will be sent at
16:01:54, 16:01:56, and 16:01:58 UTC. There is a two hour over lap between the 20 and 80m HF frequencies during the dusk and dawn transition periods.
|
Frequency |
Band |
Mode |
UTC
Hours
Time Slot |
UTC
Minutes
Time Slot |
UTC
Seconds
Time Slot |
| 3580.450 KHz |
80m |
PSK-31 |
23, 00 - 15 |
3, 9, 15, 21, 27, 33, 39, 45, 51, 57 |
0 |
| 14070.450 KHz |
20m |
PSK-31 |
00, 14 - 23 |
0, 6, 12, 18, 24, 30, 36, 42, 48, 54 |
0 |
| 144.340 MHz |
2m |
1200bps, A-FSK |
All |
All |
54, 56, 58 |
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144.390 MHz |
2m |
1200bps, A-FSK |
All |
All |
52 |
HF-APRS
Operational Schedule
PSK-31 Message Format
The
following is a typical PSK-31 message. The message includes basic
flight information and web site link, altitude, latitude, longitude, course
and speed, and GPS reception information. Thanks to Ralph, W0RPK, who provided valuable feedback and reviewed the HF-APRS system
extensively. Thanks also to Jack, W7JLC, for reviewing the band plan
and Kent, AB7OA, for reviewing the data format and HF power amplifier
design.
Balloon QSL www.kd7lmo.net
1654utc 30,510ft N33d16.75m W112d00.24m 026mph@264d 1.3dop 24F 35rh 120p
QSL www.kd7lmo.net
The following table contains the message measurands and description.
| Measurand |
Description |
| 1654utc |
Time of report in UTC hours and minutes at 16 hours 54 minutes. |
| 30,510ft |
Altitude in feet reporting 30,510 feet. |
| N33d16.75m |
Latitude in degrees and decimal minutes at North 33 degrees, 16.75 minutes. |
| W112d00.24m |
Longitude in degrees and decimal minutes at West 112 degrees, 0.24 minutes. |
| 026mph@264d |
Speed and course over ground at 26 MPH (Miles Per Hour) at 264 degrees |
| 1.3dop |
GPS DOP (Dilution of Precision) figure of merit is 1.3. |
| 24F |
Internal payload temperature in degrees Fahrenheit at 24 degrees. |
| 35rh |
Internal payload relative humdidity at 35%. |
| 120p |
Number of times the ballast pump has engaged to run. |
PSK-31 Message Format
APRS Message Format
The following are typical
APRS packets generated using 1200 baud, A-FSK. Three different APRS messages are generated. The first is a plain text status message. The elements contained in the message are shown below. The second is a NMEA-0183 GPGGA message that provides altitude information. The third is a NMEA-0183 GPRMC message that provides course and heading information. The order of each message type is rotated during each reporting period so a different message type is the last one reported. THis allows radios, such as the Kenwood D-700, that display only the last message, to display a different message.
>Balloon 05:53:30 30090'
101520'pk 0.7dop 12trk 82degF 33% 12pump www.kd7lmo.net
$GPGGA,170656.00,3303.9792,N,11159.9748,W,1,09,0.9,4703.3,M,,M,,*59
$GPRMC,170658,A,3303.9725,N,11159.7845,W,24.8,88.9,151103,,*03
The following table contains the APRS status packet measurands and description.
| Measurand |
Description |
| >Balloon |
APRS Status message to indicate the message is from a balloon. |
| 05:53:30 |
Flight time in hours, minutes, and seconds. |
| 30090' |
Current altitude in feet. |
| 101520' |
Peak altitude in feet. |
| 1.3dop |
GPS Dilution of Position. DOP is used to determine the accuracy of the current GPS solution. An DOP of 3.0 or less indicates the GPS accuracy is very good. The DOP is provided in the telemetry string to determine what happens if the payload is tumbling after a balloon burst or if the package lands in an unusual attitude. |
| 12trk |
Number of tracked satellites that are used in the fix solution. |
| 82degF |
Internal payload temperature in degrees Fahrenheit. |
| 33% |
Internal payload relative humdidity in the range 0 to 100%. Well, hopefully not much above 60% anyway. |
| 12pump |
Number of ballast pump cycles designed to dump liquid ballast. |
APRS Status Packet Format
Operational Note
Note, the frequency schedule is subject to change from flight to flight
depending on band conditions and the antenna design we are using.
Check the Yahoo
Group Page or ANSR web site for additional details.
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