Monday, January 21, 2008

Make your own vacuum tubes?

This French ham makes his own triodes. The link has a movie of him doing just that. And he does a noce job, even shows the final product working.

It's a long video at 17 minutes, but worth looking at. It was first blogged on the Make Magazine website. The first magazine devoted entirely to do-it-yourself technology projects. If you haven't heard of the magazine, check it out next time your at Barnes & Noble.

And if your up to it:

Thursday, January 10, 2008

Poorman's P25 / D-Star repeater using Maxtracs

This diagram on how to use two Motorola Maxtracs is from Tim Warth, AA2RS.

This is perfect if you don't have the 3 grand to put up a D-Star repeater or can't find a good deal on a Motorola Quantar for P25.

Remember this mod is transparent. ANYTHING it hears that breaks squelch, including intermod and spurious noises, will get repeated. Data is not regenerated.

As shown, the TX audio must be routed to the new point of entry, otherwise, it gets filtered and 4 level FSK won't pass. It's recommended to do the Maxtrac power mods and putting active cooling on the radios as these radios get hot.

In most cases a carrier system is less than desirable. Fortunately Rick Parrish, KD4VXY (the author of Unitrunker) has written a software based NAC decoder. Unfortunately at this time it it does not yet have support to provide a serial or parallel port logic output.

It's worth looking at the CML Microcircuits CMX7031, and CMX7041 datasheets. It's A C4FM baseband data processor chip.  After some microcontroller coding, this could work similar to how the D-Star node adapters work.  (Those typically use the CMX589AP4 chip)