Cooling the tranceiver

Cooling the tranceiver

Replacing the existing cooling unit to increase cooling power on the outdoor unit.

Rationale

The existing cooling unit was based on a radial fan that happened to fail and could not get replaced easily in Thailand.

The Loral 8200 serie tranceiver is designed as a sealed unit, with the bottom side being the heat skin. Cooling is provided by a forced air flow on the heat skin.

A new cooling unit was designed and installed that is based of two standard fans like those that can be find in most of the power supply units of micro-computer.

Temperature and P/A attenuation graph It is hoped that the new cooling unit will help reducing the high variation of temperature and corelated variation of output power.

Red curve is the P/A attenuation (in dB), blue is the P/A temperature (in Celcius degree), green is the radio temperature (in Celcius degree). Data and graph are collected by monitoring the ODU.

It has been observed that an automatic attenuation of the P/A (ODU output power) is applied to the signal as soon as the temperature of the amplifier goes over 48 Celcius degrees. I beleive that this attenuation is such that it helps limiting the raise of temperature in the P/A.

Design

The following views represent the cooling unit has it has been designed.

Two fans are located side by side and I beleive it provide an increased air flow on the heat skin of the ODU.

Fig 1: Side design
Side view

Fig 2: Fan side design
Fan side view

Note that the fans are located to force the intake of air, instead of being located at the extraction of air. This is to follow the design of the original cooling unit.

Also note that on the original design, the fan was activated only when the ODU had reached a certain temperature, while now they are always working.

Power supply

Power to the unit is provided by an external micro-computer power supply, taken from an old machine.

Although the ODU can provide power to the fan, it is 15 VDC instead of the 12 VDC used by PC fans and it may not be designed to provide power to 2 fan units.

The power supply is connected to the main UPS used for all the equipment of the earth station.

Installed unit

Pictures below represent the unit as it has been installed on the ODU.

Silicon join is used to provide a better isolation to the rain as well as to force the air flow on the heat skin. Silicon join is also used to isolate the power cable.

Fig 3: Side view
New cooling unit Fig 4: Fan side view
New colling unit

Results

No result was gathered with the original colling unit. So the value compared are between the two fans used without the external frame and the actuall cooling unit.

I beleive that the frame helps forcing the air flow on the heat skin of the ODU, and then providing a better cooling of the unit.

One week ending on Marsh 9, 14:26

One week after Marsh 10.

Rain also has a cooling effect as it can be observed on the picture below. The data correspond to Friday March 24th, 2000.

Olivier Nicole Last update: Apr 2000