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W4JBM's Low Frequency Activities Page

In mid-2008 I became interesting in chasing non-directional beacons (NDBs) on the low frequencies. I'd never done any serious LF listening before and quickly became hooked. From there, it was a small step to become interested in getting my own Part 15 station on the air. That's still work in progress (along with applying for a Part 5 experimental license for less restrictive LF operation), but this page will link to various information I gather along the way.



Below is a picture of my bench where I'm testing a lash up of a keying transistor circuit for my LF transmitter.

Here's a close-up of how I've mounted the transistor and heatsink. In the interest of recycling, that is actually spent .38 special brass that's being used as a stand-off.

And here is a PIC based keyer for beacon operation (left, with various speeds from 5 wpm to QRSS-60 selectable via the DIP switches) and the oscillator (right, a pair of 11.0592MHz crystals in a VXO configuration and then divided down to around 346kHz). There's a shorting plug on the oscillator because it can be keyed if you want, but in the design I'm going with now the keying will be done in the driver and the final.

This is a bit blurry, but this is the driver board. It takes the oscillator input, divides it by two to come up with a clean square wave, and then uses a pair of push-pull drivers that will each drive a MOSFET in a Class D final.

I still have the keying stage to finish, the MOSFET finals to wire in, and the output transformer to wind. I'm hoping to have this on the air for Part 15 operation this summer and be ready for Part 5 operation by late next fall.


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