[time-nuts] semi-OT: comparison of two 10x scope probes / cheap OCXO

Bob Camp lists at rtty.us
Fri Mar 18 11:48:40 UTC 2011


Hi

Some of the probes are pretty good. Others are a disaster fidelity wise. Always good to check one before buying a bunch of them. The tough part is that some of the bad ones look just like the good ones. 

Bob



On Mar 18, 2011, at 2:38 AM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:

> The cheap probes probably lack the resistive inner conductor in their interconnecting coaxial cables.
> This results in a poorly damped transient response.
> 
> Bruce
> 
> Eric Garner wrote:
>> I too, fell for the siren song of cheap Chinese probes. 2 years after
>> I bought 4 of them, only one has not failed. However, my 1980's
>> vintage probes from Tek still work dandily.
>> 
>> 
>> 
>> On Thu, Mar 17, 2011 at 12:47 PM, beale<beale at bealecorner.com>  wrote:
>>   
>>> Yes, I am controlling the OCXO frequency with a voltage input (center tap of 10k trimpot from +5V to ground). I hooked up my custom 26 MHz PIC divider* and was able to trim the OCXO to match the output of my GPS 1pps signal to better than 1E-9 (at least for short periods of time).
>>> 
>>> These parts draw about 60 mA at +5V in operation in a 23 C ambient environment, after a brief one-time warmup pulse of about 200 mA. The can gets a bit warm if left open. I taped a small thermistor against the case, and made a little styrofoam box to nest snugly over it and measured the can case temp to reach about 50 C when thus insulated.
>>> 
>>> I am accumulating some performance data on the two units I have and can post it online if anyone is interested.  (actually, I was thinking of buying a bunch more before posting the data, because the price seems too good to be true).
>>> 
>>> * http://www.bealecorner.org/best/measure/time/source/
>>> 
>>> Scott Newell wrote:
>>>     
>>>> That's a great price for any OCXO. Do they have EFC? (I can't tell from the part number in the auction photo.)
>>>>       
>>> At 01:41 PM 3/17/2011, beale wrote:
>>>    output of a 26 MHz Pletronics OCXO in a 14DIP can (by the way these go for $2 online, the cheapest OCXO I've seen).
>>> 
>>> 
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>>>     
>> 
>> 
>>   
> 
> 
> 
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