The 4-SQ PCB is designed to be used with hybrid couplers similar to the COMTEK boxes. This requires a bit more skills than building the other antenna switches, since to get the best functionality the box requires some tuning. It is pretty well described on TK5EP website and also in the ON4UN book.

The 4-SQ PCB as all other switches has got at least 105 um copper thickness and handles OM-3500 power levels without any problem.

Note that I labeled the antenna ports different from TK5EP. The control cable is identical but on my board,


TK5EP 4-SQ description

Bill Of Materials

List compiled by G4AON if ordering from rapid (note it’s for the 6×1 but most parts match)

4-SQ schematic – Note that the 800pF capacitor value is different depending on which band it’s built for

Top view of the board – If used as a drilling template, make sure to print it as 1:1 scale.

  1. Hi

    Why the “big” capacitors? Is the voltage really so high?
    I heard from DF6QV that 500-1000 volts capacitors should do the trick.
    His 4-SQ box for 40 meters did great in the fieldday with the “legal limit” of an ETO or Alpha …

    Just a question for understanding the capacitors on the picture..


  2. There is not any need to have such big capacitors. The voltage is as you said not very high, but that was what I had in my junkbox and it will handle QRO for sure, so I used it. The solder pads on the PCBs are designed so that you can put whatever kind of capacitor you wish to use. Anything with good dielectric (NP0, silver mica etc) so that losses are low will be just fine.

  3. Hi Micke,
    what is behin the joke in the 4-square pcb text: “not to be used in Finland…” ?

    The tower you got from Gällivare is a bit familiar to me,
    we were installing 40m and 20m stacks there in 1983 and it seemed that Börje’s “YL” from Australia was able to cook only chicken, so we were eating chicken 10 days in a row.
    When I came home my XYL was first serving me – chicken!

    Tapani, OH5BM

  4. Hello Tapani

    Ahh, yes I got some information from Giselle about when the tower was put up. It was very fun to hear and I also found an Absolut Vodka bottle around the base of the tower. Where you the guilty ones or Börje? 🙂 The tower is in great shape even though it is very old and a lot of the material from the beams (mainly booms) have been able to be used again, so it saved me a lot of money. We got it all for free if we just took it down.

    The joke about the 4-SQ PCB is that I originally made the board for SM3SGP (SK3W) and I knew that he would sell a few of the boards to Juha, OH1JT @OH2U. So that is why I put the text there just for fun. The Tord comment is that he has burned up a couple of 4-SQ boxes so that is why I put “The Tord” which is of course the legendary SM3EVR.

    You should come and visit sometime.

    73 de Mike, SM2WMV (SJ2W)

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