[time-nuts] HP 105B Modification

[Bruce Griffiths]

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