--- In LTspice@..., John Woodgate <jmw@...> wrote:
In message <kt5rjr+q9qr@...>, dated Mon, 29 Jul 2013, Helmut
<helmutsennewald@...> writes:
Be aware that all the components have inductance of 0.5nH to 1nH per mm
of wire length.
Specifically, that silver wire is an *inductor* and needs to be modelled
as such. You can find formulas for the inductance of a wire of specified
dimensions on the Internet.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Why is the stapler always empty just when you want it?
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
People (especially radio amateurs) get very hung up on using silver plated wire for inductors. Anyone with an iota of curiosity (read: diligence) can quickly establish that the conductivity and skin depth advantages of silver over copper are less than 6%. Given that the Q of an inductor is influenced far more by geometry, that is where to focus.
At 900MHz, the circuit should be modelled with most of the parasitics of components included, but frankly the circuit is such a bag of worms that it's probably not worth the effort. It was probably published after having been built once. Horrid. Yes, one of the major issues with this design is that in practice, the antenna matching will affect the frequency of the oscillator because there is little isolation, as the input impedance of the 2nd stage defines the output load of the oscillator stage. The tapped inductor in the amplifier output is intended to be an autotransformer, i.e. K>0, otherwise it wouldn't have been drawn thus.
I think the professor is just having fun with his students, although there an alternative interpretation.
It is definitely possible to use LTspice for RF simulation, even though it is not the ideal tool, because it doesn't really handle S parameters and transmission line structures natively. It requires quite a lot of additional work to fill in the gaps. Nevertheless, it is free and otherwise unrestricted. For oscillators and other non-linear RF circuits, however, it is about two orders of magnitude slower than harmonic balance simulators. That may or may not be important to you, possibly depending on whether you are being paid for what you do.
Regards,
Tony
Tony Casey