[time-nuts] HP 105B Modification
Ed Palmer
ed_palmer at sasktel.net
Wed Dec 9 17:42:28 UTC 2009
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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