Installing a Small Wonder Labs Freq-Mite in the MFJ-9420 SSB Travel Radio

The MFJ-9420 SSB Travel Radio is an excellent little rig for portable SSB operation. It is a mono-band 20 Meter Rig with an output of approximately 12W PEP on SSB and it has a very potent Speech processor which makes the rig sound like it is putting out a lot more power. One complaint I had with this radio was that the analog dial made it difficult at times to figure out what frequency you were on, as resolution is at best 5KHZ. My solution to this "problem" was to install a Small Wonder Labs Freq-Mite. The Freq-Mite is a PIC Microprocessor-based frequency counter with Morse Annunciation. The remainder of this page documents the steps required to get it working.

This photo shows the finished product. Note that the only external change is the sub-minature SPST (normally open) switch that I added to the upper right corner of the front panel. Momentarily depressing this switch outputs the last three digits (KHZ) of the VFO frequency via the receiver audio chain using Morse code.

Assemble the Freq-mite according to the instruction manual. There is a +5kHZ offset between the VFO frequency and the MFJ 9420 Dial readout (I suspect that the IF Frequency of the 9420 is actually 9.995MHZ not 10MHZ as the manual states, this would explain why the VFO frequency reads +5KHZ higher than expected.)

The solution is simply to program an offset into the Freq-Mite as follows:

Where the 1 corresponds to a jumper in place, J1 corresponds to the J1 marking on the board.

As far as connections from the Freq-Mite here is what I have done (All location references assume that you have the 9420 with the lid off and the front panel facing you.):

• AF - I have two 100K resistors in parallel (ie 50K ohms) mounted on the Freq-mite board at the AF point and a wire coming off of this and going to the right hand side of R23 (ie junction of R23 and C40). This injects the audio just before the point where the audio is muted on TX.
• GND goes to one side of the SPST (normally open) mini-switch.
• S1 goes to the other side of the switch.
• V+ goes to the back right hand pin on the front panel power switch.
• RF IN goes to pin 6 on U7 (make sure that you understand the PINOUTS for the NE602 before doing this).

The above picture shows the wiring and position of the Freq-Mite (lower right hand corner) in the MFJ 9420.

The following below shows the V+ connection from the Freq-Mite to the power switch on the rig front panel (blue wire).

Note that I chose to solder the conections to component leads on the top of the board. Purists may cringe at this but this was simpler than trying to route the wires to the underside of the board and figure out the correct pads for the connections.

The board itself is grounded via the screws and L bracket holding the board onto the right front metal standoff intended for mounting the add-on CW adaptor. Note that I bent the Freq-Mite L-bracket so it was flat. This allowed me to mount the Freq-Mite board parallel to the 9420 main board.

If you have the optional CW adaptor installed in your 9420 you will need to make other provisions for mounting the Freq-Mite board inside the rig.

This installation has now been verified on two rigs, mine and the one belonging to Ray, KA8SYX and is working very well.

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