[time-nuts] Fury Interface Board simulation results

[xaos]

Bruce Griffiths wrote:
> George
>
> In the JFET frequency doubler:
> 1) Surely the 50 ohms should be is series with the the voltage source V3
> for the simulation?
>   
Correct. I did a cut and paste "without rotate" there.
> 2) Usually a 1:4 impedance ratio step up transformer on the input is
> about right with a similar transformer used to step down the output
> (perhaps an even higher impedance ratio transformer (8:1, 9:1?? may be
> better). The maximum turns ratio depends somewhat on the maximum
> allowable drain voltage swing which in turn is limited by the drain
> supply voltage.
>   
I will re-run with the this in mind and will repost.
> In the voltage offset circuit:
>
> 1) The junction of R9 and R12 should be connected to the offset source
> (+5V??).
>   
This is what I didn't get about the original circuit.  I was scratching 
my head as to the purpose of a variable R9 when
the only value that made sense was when it was set to the "0" position.

> I dont understand what the 7812 does in this circuit.
>   
It was there in the original circuit so I modeled accordingly. Actually 
I ran some simulations with PS voltage variation
to see the effect as well. In that case I removed the 7812.
> Isolation amplifier looks OK.
>
> Bruce
>   
This is a very nice design and the AC analysis shows a bandpass around 
10 MHz with 20 MHz BW.

The only issue I see there is that it needs 50 parts of 6 different values.

This might be difficult to implement on a small board and would be prone 
to error for people trying to
assemble their own board.

The way I see the final product is a bare board and possibly a kit. It 
has to be easy to assemble and minimize
errors.

Actually, I was looking at the isolation amplifier provided in the C.M. 
Felton Paper:

http://www.darksmile.net/ee/Superimposing_Low-Phase-Noise_Low-Drift_Instrumentation_Techniques_On_RF_Design.pdf

It is relatively simple and would use similar devices as the Frequency 
doubler.

I will upload more info as I compile it.

George