John,

We were just having a similar discussion on sci.electronics.design, although
it was about switching in capacitors on the ADF4360's L1/L2 pins rather than
different inductors. One of the comments -- from Michael Terrel -- was that
he's worked on equipment that shorted out inductors at various taps to change
ranges. You might get some ideas from reading the discussion:
http://groups.google.com/group/sci.e...cdc83a3cf9a3d5

One problem with the ADF4360 is that the DC bias is, of course, ground on both
ends of the inductors so the RF swings above and below ground, thus requiring
either fancy bias arrangements or devices such as MOSFETs or PIN diodes that
will conduct on both cycles with a single-ended control voltage.

wrote in message
ups.com...
I'm playing with a homebrewed receiver design and need a LO which
covers 120 to 240 MHz. What's the feasibility of using something
like the MAX4545 to electronically switch the ADF4360-8 VCO's
inductors in order to cover that range?

Well... the tuning range is 1.2:1, so you'd need at least 4 -- probably 5,
more practically -- switched inductors to cover the range. I suspect you
could make this work, although the "grounded tapped inductor" approach is
probably a little cleaner.

What other approaches
are recommended for a homebrewed digitally controlled LO which
covers that range?

DDS chips! (E.g., AD9858.) The main drawback is that they consume
significantly more power than a VCO/PLL combination and none will directly
synthesize frequencies much above the low UHF range. But for 120-240MHz on
mains-powered equipment, DDS would work well.

---Joel