Welcome to Ham Radio DX!

Amateur Radio Blog Posts

Want to learn more about Ham Radio?

SUBSCRIBE to the Ham Radio DX channel

youtube facebook new-instagram-logo-png-transparent-light twitter2



Converting the Hamtronics R303 to frequency agile

19 July, 2016 - Reading time: 3 minutes

The Hamtronics R303 can be ordered with up to 4 frequencies programmed, which are selectable with jumpers.

When I ordered my R303, I had ordered CCARC frequencies to be programmed.  Now that I no longer affiliate with the afore mentioned I needed to add new channels to the receiver.  Two options are available.  Order a new IC with new channels, or mod the receiver to accept the older style Hamtronics frequency programming via DIP switch.  I chose to mod the receiver to make it completely frequency agile - this will keep it going well into the future if Hamtronics cant update the micro for whatever reason, and I can reprogram it at will.

The process is relatively simple.

The R303 uses the LMX1501 PLL, which is a serially programmed device.  A microprocessor (U1) is programmed at order time with the channels required.

As chance would have it, the older R302 runs the same PLL, reference and IF frequencies, but has a different micro with DIP switch inputs allowing it to be fully frequency agile within the band.

A MC68HC705J1A was ordered from Hamtronics configured for the R302 in the 2m band.

The circuit around R302's U1 was duplicated onto some prototype board, and the connection to the R303 was made with wires attached to a 8 pin chip socket that plugs into the original U1 chip socket, making the mod fully reversible.

Thats it, done.  Now the receiver can operate anywhere in the 2m band, and in particular not on CCARC channels :)

This receiver is in 'MY' high performance home made repeater.  The exciter uses DIP switch frequency programming already, so no mod necessary.

In future I will present an article on the complete repeater, and its associated 120W PA.