FT-225R External VFO

Introduction
The FT-225RD series have useful switching to allow selection between VFO and MEMory, in combinations of rx/tx/both/neither. Since very few memory units were fitted, I thought it useful to use this switch to bring an external VFO into use.

Schematic
Colpitts with BC-547. The '225R VFO tunes 8.2 - 9.2 MHz, the VC is padded to ensure bandspread of the DX section of the band only. Without the padding of 138pF, it would tune over ~2.5MHz. The BNC socket is normally used; the phono socket's only needed to power it up independently of the '225.

Interfacing to FT-225R
Under the '225 there is a blanking panel that would be removed if the MEMory unit's fitted. The square plug for the MEM unit was tapped into at this point. The panel was fitted with a bias-T to power the external VFO, and block the '225 VFO fromm leaking out to the external unit.
Brown - 12V permanently to ext VFO
White/yellow - 8V when ext VFO is enabled on front panel

The underside of the Blanking Panel was fitted with the smallest connector I coudld find, to prevent snagging against the operation desk. Alternatively, the rear panel DIN socket could have been used. Note the white replacement for a broken back 'foot' - a toothpaste tube top.

Summary
I had the external VFO sat to the right side of the 225. It became routine to be able to switch between internal and external VFO, so much so that when I removed it for these photographs, I really missed the functionality. It would benefit from being in a heavier case, to prevent being knocked around on the operating desk. That would also allow a slow motion drive to be fitted to the front of the existing diecast box, and hidden from view.

Specification
Range: 8.2 - 8.5 MHz
Stability: 150Hz overnight after warm up.
Output: 10dBm into 50 ohm.
Harmonics: >35dB down