Re: Replacement part for IC4 #fst3253

Shirley Dulcey KE1L

The LVC parts are lower voltage which means lower receiver dynamic
range. Not a good tradeoff in most ham designs, though it might be
okay for an ultraportable rig that prioritizes battery life rather
than performance.

The SN74CBT3253 remains available in SOIC for now. But the long term
trend in the industry is toward smaller packages so its days may be
numbered as well. The opinion among hams also seems to be that the ON
version of the part is a better performer as an RF mixer, though I
haven't seen any comparison tests anywhere.

Using these analog switch ICs as RF mixers is an off-label
application, so we can't count on the manufacturers catering to our
needs. But the fact that they are used in huge quantities for other
purposes is what makes them cheap.

I don't see my suggestion that ham designers switch to the TSSOP
package as pessimism, just an acknowledgement of the realities of the
business. Demise of the SOIC may increase the cost of repairing older
radios but that has always been an issue; as electronics manufacturing
shifts the parts to fix older things become harder to get. Just try
finding new vacuum tubes or even 1/2 watt carbon composition resistors
to fix your boat anchors! (Fortunately there are still plenty of used
and NOS tubes at reasonable prices to repair most radios. You can
still get those resistors but they're much more costly than they were
in their heyday.)

On Wed, Feb 6, 2019 at 12:08 PM Kārlis Goba <karlis.goba@...> wrote:

Why the bleak pessimism? There are other SOIC equivalents like sn74cbt3253 or sn74lvc3253 still around and not phased out as far as I know.

Karlis YL3JG

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