[time-nuts] About HP10544A

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Mar 7 20:12:40 EST 2009


Esa Heikkinen wrote:
>  > Its probably better to increase the emitter current to 40mA or
>  > so and place 47 ohms between the emitter and the output coupling
>  > capacitor a and accept the resultant +7dBm output.
>  > The transistor dissipation will increase and it may be better to
>  > substitute something like a 2N5943, 2N3866, 2N 5109, BFW16A
>  > or similar.
>
> I don't have those 2N types but after some digging found 2N2219A. 
> Changed that and 47 ohms from emitter to the ground. I run it first with 
> 6 volts, then with 9 volts and then with 12 volts but have to stop with 
> uncomplete sweep because it become very hot.
>
>   

Thats why I suggested transistors in T05 or T039 cases so that you can
use a heatsink.


> Increasing the current does help with amplifier linearity but not so 
> much. However the spectrum looks little bit better now but it's still 
> out of spec:
>
> http://www.amigazone.fi/files/gpsdo/544-7.png
> http://www.amigazone.fi/files/gpsdo/544-8.png
> http://www.amigazone.fi/files/gpsdo/544-9.png
>
>   
>> About the only way to achieve the distortion you observe is if the
>> capacitance of the wire connecting your emitter follower to the 10544A
>> output is too large (around 50pF or more).
>>     
>
> It's about 30 cm. long microwave coax taken out from some RF stuff 
> (maybe old cellphone). It's measured capacitance (at the other end free) 
> is 36,2 pF.
>
> I'll send the picture later if still needed..
>
>   
Esa

36pF from the cable plus a little additional stray capacitance is
probably more than sufficient to cause most of the observed distortion.
Try using very short leads (< 5cm long) to connect to the emitter
follower buffer.
You need to keep the capacitance < 10pF or so.

Bruce




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