Working in a Ham Radio shop part-time as I do, I get to play with the new radios that come out. The problem that creates is an ongoing recognition that I have Champagne tastes on a Beer budget, thus I work with the radios I have at my disposal. I began researching high-impedance Panadapter Tap boards and decided to take the plunge. A high-impedance board won’t load down the IF versus just simply plugging in a SMA cable to the tap point, and the cost is under $40US shipped.
I settled on the product from KD2C Dave Calo, and he has a number of boards to choose from. Shipping was quick and the product is well-built. This is an intermediate to advanced level job and is, in no way, plug and play.
As this hasn’t been documented anywhere yet, I needed to tear down the radio and plan my steps carefully. First step was to load up the board in my circuit board vice and get the wiring soldered up nice and neat. My large lit magnifying lamp made this easy. Next time I’ll run the wires first then solder the IF Tap board afterwards; handling the board inside my radio with wires attached proved to be a challenge.
Then I started planning where the SMA connector would be mounted. I elected to remove my grounding stud as it’s easy to relocate.
I needed to drill out the hole 1/4″ to allow the SMA to pass through, and used a 3/8″ bit to countersink it as the provided SMA wasn’t quite long enough for the thickness of the Kenwood’s casting. A quick pass with a sanding wheel on the dremel took off excess material, and a black Sharpie marker cleaned up the areas where I didn’t plan to take off paint.
With the physical mounting out of the way, I moved on to removing the RF board for the power tap. In retrospect I could have drawn power from anywhere, but given the IF board is directly below the RF board, this seemed simplest. I set about removing all connectors and the front panel screws, which of course means removing the VFO as well. Along the way I broke a lead to the backlight bulb but wouldn’t discover this until into final assembly, which meant an unplanned LED swapout. A LED swapout for these rigs is a common modification anyways as the small amount of heat off the bulb will cause these VFOs to drift a bit.
Removal of the board means either unscrewing the gear assembly bolted to the front panel or unscrewing the gear assembly from the shaft. I chose the former given the tight working space. I then ran into this wire poorly run at some point in the rig’s lifespan. I landed up snipping it (and resoldering later) as it wasn’t long enough to back the board out around it.
Once the RF board was removed it was simple to identify the location for power. No way to confirm it with the board and all jumpers removed, but it is right off the 9V rail pin. I went through a similar process with the IF board for it’s tap point.
The IF board sits underneath the RF board and is easy to route the wires for the Tap. It has more jumpers on it than Carter has little liver pills (Mom used to say that). The good thing about these older Kenwoods is that each jumper is unique in pin count AND has a stamping on the circuit board and connector indicating it’s position. Still, unplugging all these connectors was a 5 minute job. Like the RF board this one is a bit tricky to remove, but at least there were no errant wires where they didn’t belong. In the end when you plug them back in, work from the outer edge of the board to the inner.
In the end I mounted the board on top of the VFO using a bit of the provided double-sided foam tape. Neat and tidy.
What I’ve landed up with is a second receiver that uses the radio’s circuitry up to that point (including my antennas and phase noise cancellation. It’s kind of like a local diversity receiver and has about a .2 second delay. I’ve hooked it up to one of the SDRPlay series receivers. The IF Tap shows on display a span of 250kHz plus or minus my current VFO frequency.
And really, it’s the best of both worlds. Old-school meets new-school receiver technology fed by the same antenna system. And with a 2nd receiver, I’ll finally be able to work split 🙂