🚀 go-pugleaf

such questions are good questions and large signal RF amplifier design is an
involved subject. I've never met many (any?) people locally with these
skills and I have only limited ability in this area however, I suggest the
following;

1. Perform a class A dc bias design.. .ie... probably no collector
resistor... only an emitter resistor setting max collector current.
2. Choke the collector supply line with a RF choke (10uH probably will do).
( you could also use a tank here... but dampen it with a resistor for a
wideband signal)
3. Bypass any emitter resistor you have with a suitably high capacitor (1nF
will probably do)
4. determine from the spec sheets the equivalent input/output impedance of
the transistor at the supply current levels set in the bias design at the
frequency of interest.
5. design an output matching circuit to match the input impedance of the
antenna under test (eg. if using a 50ohm whip) to the transistor output
impedance via a dc blocking cap (1nF again). For a short wire, impedance may
be high and you could probably dispense with the output matching circuit by
feeding directly to the collector.
6. design an input matching circuit to match the 50 ohm driver to the
transistor input impedance via a dc blocking cap (1nF again).

(no 4 is the trickiest as not all manufacturers include that info)

bindy

"rigg" <riggdm@hotmail.com> wrote in message
news:4192c4ff$1@news.alphalink.com.au...
> I have a tv modulator, ch0 46MHz, and I want to boost its output with a
> simple one transistor amp connected to a short antenna so it will transmit
> up to about 20 metres. I was thinking of using a 2N3866 in a class C
> configuration with a 12v supply. Can someome give me advice on how to
select
> values or provide a simple circuit so I can do this? I am not sure how to
> pick values when using a short antenna of 30 cm. I assume matching
> impedances must come into this somehow... I have seen lots of circuits on
> the web but they are for much lower frequencies. Thanks Rigg
>
>