I was thinking that I might be reinventing the wheel by designing a
buffer amp. You guys have almost built the entire car! Thanks again
for the ideas. It'll take me a while to get it built and tested.
Ed
Bruce Griffiths wrote:
John Miles wrote:
If it helps I can send you some LTSpice schematics so that you can
simulate the circuit for yourself.
The breadboards behave as predicted by the simulations at 10MHz.
John Miles has done some preliminary phase noise measurements on his
version.
The transformers are wound on binocular ferrite cores.
I used some 14mm (long) cores intended for 40MHz to 220MHz (I had
some)
operation in my breadboard which works well at 5MHz and 10Mhz.
You can also use an off-the-shelf Mini-Circuits transformer for
low-power
applications. The T13-1 was the one I tried. I'll stick some of
the plots
up on the web later tonight if possible.
See http://www.ke5fx.com/norton.htm for measurements and connection
details
of the copy of Bruce's amp that I added to my 5061A.
-- john, KE5FX
Note the LED I used in the schematic was merely for simulation
purposes (ie LTSpice had a model for it).
A standard red or amber LED is just fine.
Another point is the LTSpice LED model isn't particularly accurate for
simulating the effects of temperature variations.
Does anyone knows of more accurate LTSpice compatible LED models?
The LED model voltage drop increases with temperature even at low
current, whilst the voltage drop across a real LED at low currents
decreases with temperature.
In practice the variation in the LED forward drop tracks the variation
in the pnp Vbe quite well.
Bruce
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