Friday, March 30, 2012

2m FM TX

Here's a duplication of LY3H design with my usual of some components by lack of them in the local electronics shop.

The original schematic:

Here's the outcome:

I didn't had BFR93 transistors so replaced by BFR91 and the BFG591 was replaced by an 2N3535. RC4558 is basically a double LM741, so I used the LM741. The tunable coil was replaced by a red core toroid with around 30 turns and frequency is set by mean of a 25pf trim capacitor.
The critical part are the first tuned circuits at 72.5Mhz, nothing a good dip meter doesn't handle, I had to remove one turn on L2 and L4 to put on frequency. Also with the direct replacement for the 2N3553 I am only getting around 0.6W, probably with some tuning 1 W could easily possible.

Since the frequency control crystal has a glass envelope why not put a LED behind to make it glow....looks like a magic eye tube. I used a double color LED, so green color when in rx and green mixed with red on tx...

The box came from an old CD-ROM drive.

I am now in the process of adding a tone encoder (top right board on the box) and a different mic (dynamic) so those results will be posted as soon as I finish it.

I'm very happy with the design and probably will be the shack main rig for repeater access.

Thank you LY3H for the design an help.

Have fun!

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