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Re: Re: MicroWave: 1296 Transverter design advice




The "Mini-Circuits" approach is based on the use of
building blocks: if everything is already matched to
50 ohms, then you can stick them together with 50 ohm
lines and be reasonably sure that the assemblage will
work.

The hassle for *me*, like just about everybody else,
is filters. While it's perfectly possible to buy a
no-tune board from Down East Microwave and cut it up
(I've done exactly this), there is nothing sacred
about no-tune - if a different filter topology works
for you, use it. If filters are commercially available,
use them.

Personally, while I am painfully aware of the shortcomings
of my PC board technique, I know my way around a lathe
and drill press, and want to have a go at some
interdigital filters. They may not be as sexy as printed
hairpins, but I can make them myself. Ditto various
sorts of waveguide filters: evanescent mode filters
are a great use for waveguide that might otherwise
be difficult to use. Or coupled microstrip with little
trimmer capacitors. Or whatever.

You can also design your radio so the front end filtering
is irrelevant, either with image-rejection, or by eating
the 3 dB SNR hit and hoping nobody will simultaneously
be on the image frequency and in the antenna pattern...

Part of why hams don't make more use of PLLs is noise.
Our obsession with narrowband modes makes stringent
demands on oscillator phase noise, which are tough to
meet with a PLL. Bricks succeed by phase locking
a very high Q cavity oscillator to a carefully designed
crystal reference.

It isn't difficult to make a PLL clean enough for FM
(cheap HTs do it all the time...), or for data. Making a
PLL clean enough for CW or SSB is a much harder problem.

Laura Halliday VA3LDH   "Que les nuages soient notre
Grid: FN03gs                pied a terre..."
                                   - Hospital/Shafte

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