[time-nuts] 4046 variations (was EPE GPS....)

[Javier Herrero]

Yes, I'm also familiarized with space qualified EEE components, and 
lately I hear the word "heritage" more frequently that I would like ;) 
The only design I've made for aircraft electronics was for a commercial 
aircraft application, and the components selection was a lot less 
restringent than for space (I think also that the system for which I 
worked was also not classified as very critical), so perhaps the 
decision to use a 4046 at its limit was driven by that heritage reasons, 
and that really there was not too much better things around :) The 
venerable 4046 has been around for quite a long time...

Regards,

Javier

Lux, Jim (337C) escribió:
>
>
> On 9/27/09 9:54 AM, "Javier Herrero" <jherrero at hvsistemas.es> wrote:
>
>> Yes, of course, some applications needs the parts that are in the better
>> side of the distribution curve for a particular parameter and for a
>> particularly stringent application, as you mention :), but I think that
>> a 4046 seems a part that should not have to be so critical that even in
>> the same lot number some work, some don't, and it is hard to believe
>> that no alternatives existed on that time that could have avoided the
>> high costly selection process.
>>
>> Regards,
>>
>> Javier
>>
>> Lux, Jim (337C) escribió:
>>>
>>> Not always marginal or poor design.  Sometimes, you can't get the
>>> performance needed with (any) part that simply meets the datasheet specs, so
>>> hand selection is needed.  Picking matched pairs is a time honored method
>>> for instance.. In some cases, the mfr does the picking for you (RF power
>>> transistors). In another case, there's an extremely low noise FET used in
>>> some charge amplifiers that not only has to come from one mfr
>>> (notwithstanding the 2N JEDEC number) but you want to buy a bunch and pick
>>> the quietest one.  High value resistors and leakage currents also come to
>>> mind.
>
>
>
> That was an aircraft radio, and while I don't know a whole bunch about what
> certification requirements they have, but for spaceflight, we often use
> older (design-wise) parts which have a "flight heritage", even though the
> performance is not what you could get with a more modern part (even if the
> new part is available as Class S). (anyone know of a flight qualified opamp
> to replace the venerable OP27.. Not that the OP27 isn't good, but a lower
> power, lower noise, wider band device is always nice to find)
>
>
> I could see the radio having been designed years and years ago, when the
> 4046 was all you could get, and even with the cost of hand selecting, it was
> still better than the alternative (dozens of carefully selected crystals and
> multideck rotary switches).  Move forward 10-15 years, and rather than go
> through the considerable effort and cost to "certify" a new design, they
> just stick with what they have.  Then, move forward another 10 years, and
> someone needs that radio repaired (I had an early 70s Piper Cherokee in the
> 80s with the original radios, and I'll bet the next owner kept them for a
> while, too.
>
>
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Javier Herrero                            EMAIL: jherrero at hvsistemas.com
HV Sistemas S.L.                          PHONE:         +34 949 336 806
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