Burndept BE-515 SARBE-6

One of my newly acquired collection items is a very good condition, fully working Burndept BE-515 transceiver. Commonly known by its designation SARBE-6, this is the 6th incarnation of the Search And Rescue Beacon Equipment (SARBE).

IMPORTANT - IF YOU ACQUIRE ONE OF THESE WITH A BATTERY - DO NOT UNDER ANY CIRCUMSTANCES OPERATE IT!!! THE SIGNAL FROM THESE IS MONITORED BY AUTOMATIC DIRECTION FINDING ACROSS THE WORLD 24/7

For very obvious reasons, before I do any general listening to this, in fact, before I will even leave it with the battery connected, I need to disable the transmitter! If your reading this, be aware that im an ex-public safety radio engineer - i have the necessary equipment to work on these safely! So what follows is just a few technical notes. Eventually, I hope to be able to not only provide instructions to safely disable the beacon and transmit features, but also conversion details to allow them to be repurposed as novel monitoring receivers.

The SARBE-6 provides automatic or manual distress beacon transmission, AM voice transmission, and short range reception, on the two international distress frequencies of 121.5 and 243MHz. You may spot that these are harmonically related. This is a dual channel unit, but the two channels are not user independent - both channels operate together. So transmission and reception occurs on both VHF and UHF at the same time.

The above is a view inside the unit. Its very complex in there! The transmitter is crystal controlled, however the receiver(s), if it follows the architecture of the mk5 model before it, uses regenerative receiver techniques. This gives the possibility of easily retuning the receive channels. One point of note, at least from the mk5, and ive no reason to think the mk6 is any different, is that the regenerative receiver stage does not have an isolating RF amp ahead of it. This means that in theory it could radiate its oscillation back out the antenna and be detected - this is why it is so important to modify these correctly!

The units were rated to be impervious to saltwater to 10m depth. How the accomplish this for the controls is quite ingenious. The casing is aluminium, and so transparent to a magnetic field. All the switches are internal reed switches, operated by external magnets! It will be partly by changing the connections to the on/off and Transmit reed switches that I accomplish the disablement of the transmitter.

My unit passes all self tests, so is fully operational - hence why I am keeping the battery off! I have tested the receiver using an external source as well.

So I have two tasks with this - disable the transmitter, and work out how to retune the receiver. If only I could find a service manual! I have the manual for the mk5, but I can see that they are not quite the same internally. If possible, I will modify it so that the transmitter cannot operate in 'live' mode, but will operate when routed internally to the BITE (Built-In Test Equipment) circuits in 'test' mode. If this cannot be done satisfactorily then I will remove the Tx crystal, disconnect the Tx supply lines, and also remove the PA transistor!