On 3 Feb 2005 07:49:33 -0800, "lemonjuice"
wrote:

Well if you want to cheat you can have more turns on the primary then
the secondary of the input transformer and you get a higher voltage
(grin). I'd have to see the exact circuit you are talking about to be
of more help.

Input transformers are all very well, but some good voltage step-up
can be obtained by carefully chosen values of hi-Q capacitor and
inductor in series between the aerial and the diode. Of course this
makes the impedance even higher, just as the transformer would, but
how strong's your signal? It might be the cheapest alternative.
--

"What is now proved was once only imagin'd." - William Blake, 1793.

On Fri, 04 Feb 2005 17:15:53 +0000, Paul Burridge
wrote:

On 3 Feb 2005 07:49:33 -0800, "lemonjuice"
wrote:

Well if you want to cheat you can have more turns on the primary
then
the secondary of the input transformer and you get a higher voltage
(grin). I'd have to see the exact circuit you are talking about to
be
of more help.

Input transformers are all very well, but some good voltage step-up
can be obtained by carefully chosen values of hi-Q capacitor and
inductor in series between the aerial and the diode. Of course this
makes the impedance even higher, just as the transformer would, but
how strong's your signal? It might be the cheapest alternative.

Yes if you use a serial resonant with a capacitor, inductor and a
resistor as you're suggesting you get voltage amplification factor
exactly equal to the Q of the circuit plus you get frequency and
bandwidth selectivity

With a transformer you get all 3 of the above without having to add an
inductor (as you use the inductors in the windings of the transformer)
plus you get impedance level shifting of the capacitance and
resistance in the secondary to the primary multiplied by the square of
the turns ratio multiplied by the capacitance and resistance in the
secondary of the transformer.
Is it worth it. I can't tell but I see more parallel resonant circuits
then serial ones .

I've actually seen implementations of the above using positive and
negative feedback circuits with an opamp to get some really interesting
results.

In real shematic for AM simple receiver, there is no ampification
bewteen the antenna (and the tuning LC circuit) and the diode. So how
the diode manage to half-rectifies correctly in real operating mode
when the signal is weak and high frequencies, which is the case of
real
radio signals.

You'll find that in reality something your simulator won't take into
account that its preferable to transmit at higher frequencies because
reception is better as the 1/f flicker noise is reduced to lower
values. Thats just 1 of the several reasons why frequency multipliers
are used in transmitters and downconverters in receivers.
I use Ansoft Simplorer mainly. Any other simulators recommended ?
Thanks in advance and best regards,