If I wanted to make a RF bandpass filter that passed 902-928Mhz and rejected
all else how would I go about that?

Haven't done it myself, but I think I'd end up doing it in several
stages.

Stage 1: figure out what sort of filter topology you need (e.g.
Butterworth, Cauer, elliptical, etc.) and how high an order you want.
There's going to be a tradeoff between the sharpness of the cutoff,
the flatness of the passband, and the number of components needed to
construct it.

Stage 2: select the component values, using either computer software
or a set of normalized-filter-value tables. If your filter isn't
terribly complex you can probably find tables in the ARRL Handbook
which will give you the correct values.

Stage 3: figure out how you're actually going to construct it. For
high-UHF frequencies like those, using leaded components is probably a
no-no (too much parasitic inductance from the leads). Surface-mount
components may work in some cases, if they can provide an adequately
high Q. My understanding is that most good filter implementations in
these frequency ranges tend to be done by using stripline construction
on PC board, using shorted and open-ended transmission line stubs to
create the necessary inductances and capacitances. The stubs could be
strips etched on the board, or sections of small-diameter coax
soldered to the board traces.

Stage 4: lay out the PC board, etch it, install any discrete
components (i.e. those not implemented via transmission-line stubs)
and any coaxial lines or stubs.

Stage 5: measure the actual response, and if necessary go back and
tweak it to adjust for any parasitic effects you hadn't accounted for.

Another approach entirely would be to check with some of the RF
component vendors. You might find that somebody has a small
surface-mount integrated high- or low-pass filter or two, which could
be hooked up in cascade to create the bandpass response that you want.

--
Dave Platt AE6EO
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