[time-nuts] HP 105B Modification

Ed Palmer ed_palmer at sasktel.net
Tue Dec 8 03:23:50 UTC 2009


That would help.  Perhaps they should be added to the web page.  I'm 
sure that I'm not the only one who would be interested.

Ed

Bruce Griffiths wrote:
> Ed
>
> 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.
>
> Bruce
>
> Ed Palmer wrote:
>> Thanks Bruce.  This is the kind of info I was looking for.  I'll have 
>> to study your schematics.  The purpose of much of it isn't 
>> immediately obvious.  :-)
>>
>> Ed
>>
>> Bruce Griffiths wrote:
>>> Ed Palmer wrote:
>>>> I have a late-model 105B Oscillator that's equipped with a 
>>>> 10811-60109 oscillator.  It seems a shame to have that nice 10 MHz 
>>>> source without having access to it.  I was thinking of adding a 
>>>> buffer amp and bringing out the 10 MHz signal.  It shouldn't be too 
>>>> hard, but before I reinvent the wheel, has anyone done this and do 
>>>> you have any suggestions or advice?
>>>>
>>>> Thanks,
>>>> Ed
>>>>
>>> Ed
>>>
>>> Amplifiers like those shown:
>>> http://www.ko4bb.com/~bruce/OCXOBufferAmplifiers.html 
>>> <http://www.ko4bb.com/%7Ebruce/OCXOBufferAmplifiers.html>
>>>
>>> work well.
>>> The gain is determined by the transformer turns ratio and the 
>>> emitter series resistor value is chosen to set the output impedance 
>>> to 50 ohms.
>>> RF amplifier transistors other than the 2N3904 can be used, my 
>>> breadboard version uses an 2N5943.
>>> Reverse isolation is about 40dB at 10MHz. If you need more isolation 
>>> just cascade 2 or 3 such amplifiers.
>>> However some attentiaon to the supply decoupling is required to 
>>> ensure that coupling via the supply doesn't degrade the reverse 
>>> isolation.
>>> In your case a nominal gain of 3dB or so should suffice.
>>> If you need it +27dBm output is possible with an appropriate RF 
>>> transistor.
>>>
>>> Bruce




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