Country update, September 2000

Country update, September 2000

Problem with the tranceiver

Traceiver monitoring

Since March 2000, we are monitoring the temperature inside the tranceiver, as well as the output power of the uplink signal.

The following graph shows the output signal power in red, as well as the temperature of the power amplifier in blue. The power output signal is shown as the attenuation applied to the nominal power output value of the tranceiver. The nominal value is 39 dBm.

First of all, we can notice that on March 9th, a new cooling unit has been added to the tranceiver, resulting to about 1dB power gain.

Some data were not collected because of software failure. The software has to be restarted manually after each reboot of the system.

The main point that can be read on this graph is that since June 2000 (1/6/00), the average power output has been decreasing by approximately 1dB per month, while the environmental conditions, as well as the configuration have not changed.

This loss of output power on our up-link ius confirmed by JSAT who monitors the signal at the satellite. From their monitoring, they can see and average loss of 0.5dB in 2 weeks.

Equipment testing

Equipment has been tested in site.

Performing UAT

While performing UAT with YSCC, some testing was conducted, leading to the following results:

even when setting the equipment to thier full power output, the signal received at the satellite is under the nominal working conditions;
chages in the modem output power could not be seend by monitoring the satellite;
some testing of the equipment had to be performed.

Modem testing

Using a spectrum analyzer, it was controled that varying the Tx Output Power value on the front panel of the modem, we could see the same variation on the output connector.

We disconnected the Tx IF cable from the modem and pluged the Tx IF output of the modem to a spectrum analyzer.

Through the control panel, we varied the Tx Output Power, from -25dBm to -5dBm. On the spectrum analyzer, we could read a variation from -24dBm to -4dBm.

It could be concluded that the modem is working properly.

IF cable testing

Although very unlikely, we checked the Tx IF cable, using the same spectrum analyzer.

The Tx IF cable was disconnected from the tranceiver and connected to the spectrum analyzer, then proceed to vary the Tx Output Power from the front panel of the modem. Same variation as above could be read on the spectrum analyzer.

The Tx IF connector was checked and found dry and free of corosion.

It could be concluded that the TxIF cable is not damaged.

Full equipment testing

From the above tests, it could be guessed that the problem is located in the tranceiver.

Since we started the satellite link on June 30th, 1997, the tranceiver had to be repaired twice, for power supply failure. Before the second failure, the same output power loss had been witnessed.

One more testing has been conducted that consisted in varying the modem Tx Output Power and reading the Power Amplifier Output Power on the tranceiver.

Four series of measurement have been done, changing the Power Backoff value on the tranceiver, from 3 dB to 0dB.

Even with no Backoff applied, the nominal power of the tranceiver, at 39 dBm, could not be reached, as the maximum reccorded value vas 36.3 dBm.

During the measurement, the power amplifier temperature remained stable at 59°C. For information, 59°C gives approximately 0.90 dB attenuation when the tranceiver is working properly (average 0.90 dB, standard deviation 0.264).