Help Request from Website`

[Andre Kesteloot]

Joseph Penrod wrote:

> Dear AMRAD:
>
> I noticed your request for help with LW projects. I
> have some experience with this, having discovered the
> LWCA in 1997. I have designed and built LW equipment:
> an analog receiver, low power antenna test beacon, and
> a Part 15, 1750M class E type transmitter. I've also
> done some programming for Linux and have some really
> nice programming aids: Qt and Glade, and PyQt - the
> Python language port of Qt.
>

Hello Joseph,
thanks for your note. Apologies for the delay in replying, but I was on
the road, involved in other things.. We definitely could do with some
help in all aspects of our existing and future efforts in the LF field.


> Now that it looks like the FCC is finally going to do
> something about a LW allocation, I have some ideas
> about LW transmitters for this as well. I've seen some
> designs posted on various web sites that could stand
> some improvement.

definitely. For QRSS (the most popular mode for the moment), on-off
switching of a carrier is perfectly acceptable, and the British have
published several MosFet designs that appear to hold their own. 
Going to other forms of modulation is much more complicated (and
usually require modulating also the power supply voltage, as low-cost
Power MosFets (such as those used in power supplies, and thus designed
for relatively low frequencies) are often unhappy operating in linear
configurations, such as class B.  (Incidentally you may have noticed
that all the high-power audio amplifiers on the market mention the word
"Power Mosfets". Yet when one examines the schematic, one usually
finds that the output stages are bipolar transistors, and the MosFets
are used to create high voltage (+/- 40 or 50 volts) from the +12v from
the car battery)    

Incidentally, if one wants to be able to transmit on LF, the new FCC
rules that will eventually come into force one of these days call for
the operator having at least a General Amateur Radio License.

Where are you located? If not in the Washington DC area, then we will be
cooperating with you mainly via e-mail !

73
André