Eliminating the VRC 353 Fan Noise

LibPic353Introduction

The VRC 353 is a very capable, fifty watt FM Transceiver designed and built by the military for use during the cold war. Its main use was in armoured and soft skinned vehicles and it provides FM Voice and Digital Operations from 30 to 76 Mhz in various configurations at ranges up to 50Km.

 

Its design makes it less than ideal for use in the average amateur shack – having been designed to withstand the electromagnetic pulse from a nuclear weapon – it is the arch-typical boat anchor – weighing 22 kg (about 50lb).

Temperature Control

Temperature control is via two fans designed to flush heat from the set by forcing air past a heat exchanger, from front to back – at a speed dependent on the internal temperature.

When the set is warm, the fans will idle reasonably quietly, but when the temperature rises the temperature control kicks in and ramps up the air flow. The mode switch allows the fans to be switched off.  They are a dead give-away in a tactical environment. The set will cut out if it overheats etc. While the noise of the set was a tolerable feature in military operations it is less attractive in an amateur radio shack because it sounds like a passing jet. A good technical description of the set can be found here.

In this article, Leighton Davies, GW3FSP creates a different user experience making the rig more acceptable in amateur use.

Having had one fan on my 353 decide to die very noisily I decided to replace the 3 phase fan with a 24 volt DC fan, (despite the availability of spare 3 phase fans).  The problem then was to find some way of fitting the new fan in the rear of the 353.  I decided to rip out the internals of one of the original fans and fit the DC fan inside its housing.

Removing the Original Fan

 

The fan is held in with 4 screws, these were removed and the fan removed.

Fan Removed

Tidying Up

I then cut and sleeved the original 3 phase wiring.

 

 

 

 

 

 

 

Making room for the 24V Fan

I then stripped out the internal motor, bearings, and fan assembly leaving a bare shell.

Fitting the Fan

Then came the hard bit, cutting out the internal casing to take the new square fan, this took some time(!) and after several hours I managed to fit the fan in the casing using hot glue to secure it in place – blowing outwards.

24V Fan Fitted – Inside View
Outside View 

Re-Fitting

I then fitted the fan assembly back in its original position with the 4 screws and ran the extended fan wiring along the spine of the 353 to the rear of the hour meter.  I used hot glue to stick the wiring in place out of the way of the outer case and other wiring.

The photo below shows the power supply wiring for the 24v Fan soldered to rear of hour meter.

NOTES

You could of course replace both fans but then the fan noise might be distracting, with just one fan replaced I find the noise quite acceptable.

After testing the fan I replaced the set into its case and bench tested it to prove it working.  Job Done!

What I might do now this mod works is to look for the same size fan but one which has a higher speed and throughput to replace the other fan, this would hopefully keep the set cool and reduce the noise.

Editors Note:

All modifications published on this site are published for the purpose of experimentation. They should be carried out by a competent and engineer and at the risk of the owner of the set being modified.