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VHF/UHF Radio Link

The VHF/UHF radio link serves for telemetry transfers from the orbiter to Earth. As a rule, the orbiter generates much less telemetry data than the payload it was launched to carry. On the other hand, when 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 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 length. On Earth, messages 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.

VHF/UHF Transmitter

Virtual power draw: 210 mA

The VHF/UHF transmitter of the orbiter most commonly operates at 145 or 436 MHz, providing 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:

int32_t transceiver_send(uint16_t tx_num,uint16_t rx_num,const uint8_t *data,uint16_t len);

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

	#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);
		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)))
		printf("Disable transceiver #%d\n", tx_num);
en/uhf_tx_subsys.txt · Last modified: 2020/03/25 16:28 (external edit)