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en:uhf_tx_subsys [2018/01/23 18:14]
ashley
en:uhf_tx_subsys [2020/03/25 16:28] (current)
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-**Telemetry transmitter** \\ +====== VHF/UHF Radio Link ======
-Virtual [[power_subsys| consumption]] - 210mA+
  
-{{ ru:​device_standart.jpg?​direct&​200|}} +The VHF/UHF radio link serves for telemetry transfers from the orbiter to Earth. As rule, the orbiter generates much less telemetry ​data than the payload ​it was launched ​to carryOn the other handwhen orbiter faces a problem threatening loss of its positioning data this link remains ​available ​for obtaining ​critical information ​on the state of orbiter support ​systems and restoring ​the satellite ​into operation. Moreover the low-rate communications link consumes less energy compared to the HF radio link.
-The spacecraft telemetry transmitter is most often a VHF transmitter operating at either ​the 145 or 436 MHz range and providing ​low data rate with an omnidirectional or near-omnidirectional on-board antenna. A high data rate is not needed here as the amount of telemetry ​information from the device is usually much lower than the data rate from the payload ​for which this satellite ​was launched ​into spaceAdditionallyif there are problems on-board and if the device loses its orientation, ​this communication channel will remain ​available ​in order to obtain ​critical information ​about the state of the on-board service ​systems and restore ​the satellite's operability.+
  
-In case of board abnormalities,​ any and all information is extremely important. ​The information allows the operational control group that is on duty at the MCC and working with the satellite in communication sessions to identify problems ​and decide how to solve those problemsIn this case, the low-speed communication channel consumes a small amount of [[power_subsys|energy]] ​in comparison with the [[hf_tx_subsys|HF radio channel]].+The VHF/UHF radio link is implemented in the Orbicraft construction set in the form of two modules: the VHF/UHF transmitter module ​and the ground-based VHF/UHF receiver module. The orbiter-generated dataset comprises a byte array of variable length ​and arbitrary structure that can be transmitted ​to Earth along with information on its lengthOn Earthmessages received during ​the communications session appear in real time in the MCC software “as is”, meaning that it would be most practical to send telemetry in plaintext.
  
-As part of the construction setthe VHF radio channel is implemented ​in the form of two modules: ​the on-board transmitter module and [[uhf_rx_subsys|the ground receiver module]]. Data transfer to the ground ​is carried out using the following ​function: ​\\  +{{ :​ru:​укв_канал.png?​400|}} 
-  int32_t transceiver_send(uint16_t tx_num,​uint16_t rx_num,​const uint8_t *data,​uint16_t len);  + 
-Under the experimental conditions ​the transmitter has the number "​2"​ (marked ​on the body), and [[uhf_rx_subsys|the receiver ​(ground)]] is number "​1"​. The array of data transmitted from the board to the Earth is a byte array of arbitrary length and composition that can be transmitted to [[sim_earth|the Earth]], indicating its length. On Earth, messages ​received ​during a communication session are displayed ​in real time in the MCC software interface "​as ​is," so it is most advantageous to transmit telemetry ​in text form.+==== VHF/UHF Transmitter ==== 
 + 
 +Virtual power draw: 210 mA 
 + 
 +The VHF/UHF transmitter ​of the orbiter most commonly operates at 145 or 436 MHzproviding a relatively low data transfer rate with an omnidirectional or nearly omnidirectional antenna. 
 + 
 +The VHF/UHF transmitter ​in the Orbicraft Construction Set is numbered 2 (the number is printed ​on the housing). 
 + 
 +Data is sent to Earth using the function: 
 + 
 +<code c>int32_t transceiver_send(uint16_t tx_num,​uint16_t rx_num,​const uint8_t *data,​uint16_t len);</​code>​ 
 +    
 +==== VHF/UHF Receiver ==== 
 + 
 +The VHF/UHF receiver in the construction set simulates ​the operation of the receiving part of the ground-based telemetry receiver station over a low-speed link. During experimentation with the “satellite” similar receivers will be mounted directly ​on the Earth surface i.e. on the globe. However the set also includes this receiver ​to facilitate preliminary testing of satellite communications. 
 + 
 +The receiver proper interoperates with MCC software. When telemetry ​data is sent over the orbiter data link and the VHF/UHF receiver ​is connected in the ground network this data will be received ​automatically by the ground-based receiver and displayed in the left pane of MCC GUI. 
 + 
 +The VHF/UHF receiver in the Orbicraft Construction Set is numbered 1 (the number ​is printed on the housing). 
 + 
 +==== A Snippet ​in C to Test the Telemetry System ==== 
 + 
 + 
 +<file c UHF_Test_C.c> 
 + #include "​libschsat.h"​ 
 + /* 
 + ** Lab 8: UHF transceiver demo. 
 + */ 
 + void control(void) 
 + {  
 + const uint16_t tx_num = 2; 
 + const uint16_t rx_num = 1; 
 + const char hello[] = "​hello,​ world!";​ 
 + printf("​Enable transceiver #​%d\n",​ tx_num); 
 + transceiver_turn_on(tx_num);​ 
 + Sleep(1);​ 
 + bus_setup();​ 
 + printf("​Send data from #%d to #​%d\n",​ tx_num, rx_num); 
 + if (LSS_OK != transceiver_send(tx_num,​ rx_num, (uint8_t *) hello, sizeof(hello))) 
 + puts("​Fail!"​);​ 
 + printf("​Disable transceiver #​%d\n",​ tx_num); 
 + transceiver_turn_off(tx_num);​ 
 + return; 
 +
 +</​file>​
  
en/uhf_tx_subsys.1516720444.txt.gz · Last modified: 2020/03/25 16:29 (external edit)