wrote in message
ups.com...
On Sep 11, 8:06 pm, "Philo" wrote:


I sincerely think you would have a lot more fun trying to clone a HW8.

There is no need to pursue much linearity in a cw transmitter ... unless
you
try to build an almost unpractical one.

Granted, Philo...

Here's how the argument goes:
- goal: minimal part count + ability to put clean QRP signal anywhere
- DC drain no problem - class C not indispensable
- linear broadband keeps part count down and adds little spurs
- do all filtering after PA, if possible with multi-tuned tanks or
plug-in LPFs


There are a few items in your project I have doubts about.

The linear amplifier, for instance. You could build a very linear broadband
amplifier with paired CATV transistors in push-pull. Those transistors
became old stuff and were trashed the moment they were replaced by IC's
(TRW, Motorola, etc.). You still can find some, but a matched pair will be
hard to come by. With some transistors you may even have problems to get
beneath 5 MHz. And forget about a power supply of 12 volts: you will need at
least 2 x 24 volts DC. Anyway, the maximum output will be around 2 volts if
you require quality. So you'll need another 10 to 12 dB to get an output of
one watt or so. This will be an even greater challenge if you want to keep
spurious/harmonics down to -40 or -50 dB.

I also doubt filtering at the output only is practicable. Once garbage got
in an amplifier chain, it is very hard to get rid of it. Since you are
considering using plug-in filters, build sets of three: use the first
between the oscillator and the driver stage, the second one between the
driver and the final stage the third in the antenna circuit.

Have fun!