There is nothing to stop anyone from hacking a small part of a PCB,
soldering the chip on to it, soldering leads on to it and making a leaded
part out of a SMT part. this is handy if retrofitting an existing etched
board design.
But for something like a filter, a Dremel etched PCB or "manhattan" style
construction with SMT parts would be no more difficult than building
point-to-point with leads-- it would probably be easier and the end result
would work better.
But yeah, if you can get the values in SMT, you can always MAKE leaded parts
out of them. Doing that is a completely valid substitution for an one-off.
Fred W0FMS
On Sat, Apr 9, 2011 at 10:44 AM, Dan Zimmerman N3OX <n3ox@n3ox.net> wrote:
> You can get every necessary value for the BC band-reject filter from
> Mouser
> (and I'm sure, Digikey) in 100V 5% ceramic surface mount type. I forgot to
> check if all were available in C0G, but I know some were, and I think all
> are... it's very standard and the correct choice for RF applications.
> Prices are low... 40 to 60 cents in Qty. 1 for some spot checks.
>
> >From what I can find the HF Q of the standard chip caps at least 600-1000
> (dissipation factor of at most 0.0015 is quoted many places, which is
> Q=667,
> some data sheets say Q>1000). And I think all this is probably more or
> less
> the same for C0G ceramic disks vs. C0G ceramic chips if dielectric
> dissipation is at fault.
>
> Intuition tells me that anything a leaded ceramic disc cap could do, a
> surface mount chip cap can do better with the exception of handling
> continuous RF currents and dissipating the resulting heat... not because
> they're more lossy (they may be less) but because they are physically
> smaller. For receiving filters this should not be an issue. For things
> like QRP low pass/bandpass filters, etc, they might. (For QRO filters
> you'd
> probably be looking for mica caps anyway. But even there, surface mount
> versions seem to be more available and a bit cheaper ($4-$5 in Qty.1) at
> least in new parts )
>
> It's not too hard to use surface-mount chip caps in dead-bug construction
> as
> long as you have a decent pair of tweezers.
>
> 73
> Dan
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