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DL8DTL - Joerg Wunsch
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There used to be a 500 Hz CW filter option for the TS-50 from Kenwood named YK-107C. When trying to obtain such a filter in 2010, it turned out to be discontinued by Kenwood, with no replacement. Despite of several shops in the Internet claiming to still sell it, it eventually turned out that all of them simply didn't notice it could no longer be obtained, so (often after already "completing" the buy with credit card details etc.) they eventually all regretted it's no longer available.

During the research, the YF-107C filter caught my attraction. It is designed for the TS-480 transceiver (which could house up to two different optional filters), and the few data that are published about this filter by Kenwood indicate it has identical electrical parameters (center frequency and impedance) as the YK-107C filter. According to the TS-480 In-Depth Manual, the new filter has a better shape factor though. Also, the filter is now optionally available in a 270 Hz version, YF-107CN.

Problems to solve

The new filters cannot be used as a 1:1 replacement due to a slightly different mechanical design. Comparing the board layouts in the service manuals of both transceivers indicated they take approximately the same footprint size though, but the YF-107C(N) filters have one additional pin, and the pins are located on the opposite corners, compared to the YK-107C:

Bottom view of YF-107CN

Top view of YF-107CN

Top view to the filter PCB of the TS-50

The function of the additional pin was not immediately obvious; the schematics indicate these pins have a static potential of 3.3 V, and they are routed straight to a pin of the microcontroller. Their purpose could eventually be guessed from a sentence in the In-Depth Manual: Since the type of filter is recognized automatically, it does not matter in which order you install filters in the slots. So it was decided that these pins could probably remain unconnected without affecting the function of the filter unit itself.


After thoroughful comparison of all details, I decided to buy the YF-107CN filter. Everything went smooth then. I soldered small pieces of wire to the filter's terminals, and mounted the opposite ends of those wires on the filter board:

Filter wired onto the PCB

Note that the TS-480 schematics indicate the pins "input" and "output" in reverse order to what the circuit itself suggests, so I decided to mount the filter the same way as the actual TS-480 circuit would use it. (Chances are good the filter behaves symmetrical anyway, so the actual direction doesn't matter.)

I soldered some strong wires to the shield terminals, and inserted these wires into the rectangular openings of the filter board, thereby bending the other wires until the filter sat on the board. As the board is coated with solder resist, there is no risk of shortcuts when applying only minimal forces. After soldering the shield connections, the filter board could be mounted into the TS-50 again. Even though the overall height of the assembled filter is now a few millimeters above what the unit would have looked like with an YK-107C, the TS-50's case offers enough spare room for it to still fit.

Assembled and mounted filter board

I'm pretty satisfied with the result. It's a really nice narrow CW filter that "makes a difference". Not only that it helps in situations where the band is crowded and suffers from QRM, it is also a dramatic improvement for weak signals that are unreadable within the noise floor of the SSB filter.

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