The Portable Repeater Project

One of my amateur radio projects I’ve got underway in a low intensity background sort of way is building a repeater that is portable - not intended to be used for permanent installation anywhere but instead intended to be set up quickly for temporary use during an emergency or for some ham radio supported event.

The general plan is:

• the receiver/transmitter will be Alinco DR-435T mk III mobile radios.
• two mobile duplexers
• a controller based on a Raspberry Pi running AllstarLink software.
• a small 120VAC power supply, along with a provision for external 12VDC power

The Alinco DR-435T mk III radios offer several advantages - they’re relatively cheap, they’re well built, and they have a connector on the back that provides access to audio in for transmit and audio out for receive, both of which are intended for connecting to a packet radio TNC. The larger point to the TNC connector is that it offers access to audio input/output that doesn’t run through the usual pre-emphasis/de-emphasis processing usually done for voice over FM. They don’t have fans, which is a problem if they’re going to operate at anything like a 100% duty cycle, something that’s common for repeaters. So I’ll have to fit an external fan to the heatsink on the transmit side.

The DR-435T mk III can do CTCSS and DCS decode and encode and offers selectable power levels of 5, 15, and 35 watts - plenty of power for the sort of use I envision.

The reason for two duplexers is that the repeater frequency coordinator for Washington state, WWARA, has set aside two repeater frequency pairs, and my plan is to have one duplexer tuned for one pair, the other duplexer tuned for the other pair, and be able to switch between the two pairs to use whichever one is better suited to the need or will avoid interfering with other repeaters.

The goal is to have this in a reasonably compact package that weighs in the vicinity of ten pounds, so it can be hauled a fair distance to get it deployed in a favorable location.

More details as I think things through some more…