MFJ 94XX Series SSB/CW Transceiver
Shown above the 10M Version
Perhaps now close to 20 years ago, MFJ (now out of business) introduced a line of single band SSB / CW (optional kit) QRP Transceivers. These were small, a single conversion design and good for about 10-12 watts.
I jumped in with both feet and bought the 20M variant. I went whole hog and bought the optional CW board and the 12VDC Wal Wart. That set me back well over $300. I should have not jumped so quickly! It suffered from VFO drift but otherwise was OK. This was a great idea as there were models covering HF as well as 6 and 2 Meters. Too bad it had an analog VFO.
Were there the Arduino and Si5351 at this time they could have gotten $500 for a 20M version.
The used market has treated these units well and often sell for well over $200 even the hardly working units. So, last week when I spotted a half a dozen units being sold on eBay by the same person an idea hit my shrinking brain. [I am told our brain shrinks as we get older.] There were three in that lot all on 75M and the starting prices were $70, $90 and $110. I decided to bid on the middle one.
So, what was my idea. Upon looking at the 75M unit, I found that there is actually a sub-panel behind the front panel which is held in place by the controls and one bolt. The plan was to remove the front panel and to make a new front panel. In place of the Fine Tune control, I would put a toggle switch for either two frequency range control or USB/LSB select.
In the upper right-hand corner (printing area), I would install a smaller version of the ST7735 color display which is less than 1-inch square. The piece de resistance would be the JF3HZN circular dial. All other controls would remain as original.
The CW capability in the original was a separate board anchored inside the case and this a place to install the ESP32 and Si5351.
I printed the schematic of the 94XX Series, and it is a single conversion design using a 6-pole filter and lots of NE602's.
There is a ton of surface mount parts and if you purchased a 75M version to put it on 20M you would need to change out the Band Pass Filter and the Low Pass Filter. Since the Si5351 would supply the LO and BFO, a simple removal of the BFO crystal is all that is needed.
Or you could keep that crystal and do like I did on a Bitx 40 to add USB to a LSB only rig. A switch changed the LO range for the other sideband to create a sideband inversion thus the opposite sideband with one BFO crystal.
The Band Pass Filter as far as I could see, in the small photo I had, is all SMD where I suspect the inductors could stay and with LT Spice you could find new capacitor values for 20M. But the LPF used discrete through hole parts so new parts could be installed for 20M.
The auction ended last night before midnight an up until three hours (9PM) before there were no bids. So, I bid $105 on the listed $90 unit. That bid was my gag level as I figured about $30 for additional parts and $20 for shipping. I was outbid near midnight and that 75M unit sold for $205.
I am glad I lost as I could build one hell of a rig for $255 which is what I would have spent in total were I the winning bid.
So, I am still looking for a commercial radio where I can install the Circular dial from JF3HZB. A Heathkit Monobander or an MFJ 94XX would gladly be accepted and I will pay for the shipping. Check your garage stash and look under the work bench and see what is lurking there. Your contribution would be greatly appreciated.
Them that know can make things go.
73's
Pete N6QW