[Elecraft] XV432 LO changed to DigiLo Synthesizer

[Mike Lewis]

A few days ago I tried FT-8 on 432 and discovered that my LO was not stable, hopping around several Hz plus drifting up to 40Hz . The 9V LO power was flat in both TX an RX, oven working. pushed, prodded, re-soldered, tuned, detuned, no change.

I recently integrated a DigiLo 6GHz PLL synthesizer with a 10Mhz double oven OCXO into my 10GHz system and it is no rock solid.  It has 255 preprogrammed frequencies, 404MHz being #2.  So today I removed C82 (coupling cap to L5 filter section)  and U2 (the LO 78L09 regulator).  Drilled a hole near the power connector for a small SMA bulkhead connector.  RG316 run from that to the C80 side of C82 PCB pad, soldered the shield to the L3 can. Set LO power jumper block to 1-2 so only on when the XV432 is selected.  Nothing to warm up inside the XV432 any longer. The oven still powers up, but the rest of the LO is powered down so no matter.  I wanted to keep all the parts inside and this can be backed out easily.  I soldered the 78L09 to the nearby ground test clip loop so it could be found easily someday.

The Digilo is around +2dBm output and the XV432 mixer wants closer to 17dBm.  Fortunately there is a MMIC amp between the LO filter and mixer (fed from the LO power jumper blocks). Feeding the Digilo at C80 runs it through L5 filter section and TP1 is at 3.1VDC.  Good enough.

Happy to say it is working great, super weak beacons I was hearing before are now spot on, 0 drift, and the K3 offset correction (XVx OFS) is set to 0.

Next up is to package the DigiLo and OCXO into a standalone metal case, add logic (CPU or 8-3bit encoder) to read the band decoder to auto set the correct LO frequency for different transverters.  I am using my KRC2 -> TTL SP4T coax relay control lines for that. Will also add a manual programming switch.  Then will convert the XV22 and my DEMI 902 an 1296 transverters, and of course the 10GHz system.

I previously changed the PA module from the Toshiba to the Mitsubishi module.  Retuned the front end, it is ready for FT-8 and other digital modes now.

Mike, K7MDL