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View Full Version : A (somewhat) quick and easy fix for a drifting VFO-120/TS-120



N8YX
06-28-2015, 07:00 PM
I recently got ahold of a VFO-120 to use with my TS-130SE/130V rigs. Only problem is...that setup drifts like crazy. I'm talking like 2KHz after power-up, then about 100Hz/15min thereafter.

One could construct or buy a huff-puff stabilizer and install it, and Kenwood published a couple of modification articles related to the problem. Or...one can simply swap the unit for that which is used in a TS-130S.

The electrical interface at the rear of the 120 series VFO is slightly different than the 130's setup: The former uses a keyed 3-pin (Hitachi?) miniature connector and RCA output jack for the VFO signal while the latter carries all signals (VFO power, ground, RIT voltage, VFO out and VFO ground) on a 5-pin connector of the same series as the 3-pin.

Almost every Japanese rig of that vintage uses the needed connectors, and I got mine (plus a shielded cable for the VFO Output line) from a junked IC-751 front panel. Some pin/wire swapping between connectors - facilitated by a fine flat-bladed jeweler's screwdriver - will allow one to attach the necessary control and signal leads to the 130 VFO. From there it's a simple mechanical swap.

Measured drift with the outboard unit is 500Hz over 30h from a cold power-up. This is 100Hz worse than the 130-series internal VFO and is well within Kenwood's specs.

Watch eBay for used VFO assemblies. If anyone is interested I'll post a few pics.