>> I've got people asking me all the time for specs that are
>>nearly
>>physically impossible on parts I sell. I tell them "something has to
>>
>>give!"
>
>
>Only in a static or degenerating product Jon.
Hmm?
Not necessarily. Take for instance a customer who wants a VCO designed
with 0 dBm output, 5mA of current draw and -110 dBc/Hz phase noise at 10
KHz. Frequency range is 54 MHz wide and tuning and supply voltage are 3
volts.
Now, if one does not care about phase noise it is a pretty simple thing
to drop current and power. However, phase noise is directly proportional
to current draw. In general, the more current, the better the phase
noise.
At the present level of technology these sort of specs are either
impossible or very costly to obtain let alone manufacture en masse.
Sure, you could probably build one in the lab, but on the assembly line
is a different story. So a compromise has to be reached.
Take another customer who wanted a high power (100 W) cavity filter for
800 MHz cellular. They wanted virtually no loss, 60 dB out of band
rejection and a size that was about the size of a small loaf of bread.
The problem is that flatness, loss and rejection in a filter all work
against each other. You can't maximize all of them to "ideal" values.
Some things are just not physically possible.
Yes, technology can improve things and make them easier. Shoot, the
components available today for working at 6 GHz would have made my life
much easier a decade ago when I was designing 6 GHz radios. But back
then I had to work with what I had.
In the here and now snapshot of the present (at this immediate moment),
all technologies must be considered static.
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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