This blog was created to share my projects, ideas, and experiences in amateur radio with other operators around the world who also enjoy this wonderful hobby.

Monday, June 18, 2012

MFJ Cub 9320 Qrp Transceiver Repair and Modification

MFJ Cub Model 9320 single conversion QRP cw transceiver. Purchased used on E-Bay a few months ago. The volume and tuning potentiometers were replaced. Previous owner or MFJ ( I am not sure if it is a 9320 or a 9320K) installed the pots on the incorrect board locations. The MFJ Cub's volume and tuning potentiometers must be soldered to the mounting pads (holes) closest to the front board edge. There is a second row of pads about 1/4 " further inside the board. If the pots are installed to the inside pads, the potentiometers won't fit flush against the front panel, thus creating excessive force and stress the potentiometers when tightened. The incorrect installation damaged both controls, the volume could not be adjusted and the tuning was unstable. After the controls were repositioned and replaced, the transceiver now works like a champ.

Transceiver's rear panel view-  Notice the antenna connector, an RCA type jack. Notice toroidal inductor L-11 through the knock out for the BNC jack installation. The MFJ Cub is in its original configuration, except for the addition of the BNC jack. Covers about 60 kHz of the cw portion on 20 meters Power output is about 2 watts with 12 vdc supplied, and a little more when connected to a 13.8 volt power supply.

Internal view of the 20 meter Cub with top cover removed. The  transceiver is supplied fully assembled or in kit form. The surface mount components are pre installed on the kit version. More information on the MFJ website

BNC connector modification, the BNC is wired to the RCA jack in parallel. The ring (ground) terminal of the BNC is bent 90 degrees, cut and soldered to the RCA's jack top ground portion. The center conductor is connected to positive (central) part of the RCA jack with a piece of solid hook up wire. The wire at the same time will prevent an UHF to RCA type adapter not (center pin cut ) to touch or damage toroidal inductor L-11 if inserted.

Comparison of two different type of UHF to RCA adapters. Needed to connect the antenna to the transceiver in its original configuration. On both connectors the tip needs to be cut or filed to about half its length, otherwise when the adapter is inserted it will touch or interfere with toroidal inductor L-11

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