a small matching unit to use the watson w2000 triband antenna on 70mhz

Submitted by gerry on Tue, 05/17/2016 - 15:34

I recently upgraded my shack to an ICOM IC7300, which in the EU specification includes the 4 meter / 70MHz band. I do not have a vertical for 4m, or space for one right now, but had read about others using a small matching unit to provide the necessary match using the Diamond V2000, or Watson W2000, as my version is badged. Two blogs I got my inspriation from are Miguel EA4EOZ's blog and that of Tony EI4DIB, so having done some reading, and some rummaging in the junk box to see if I had the requisite parts, I got to work.

I first wound an inductor... estimating by eye from the work of Tony and Miguel. I used a pen with a diameter around 8mm, and wound 4 turns, spaced around 3mm. I then stripped down a rubbish old antenna switch, which provided a case and some SO239s.

I then drilled some holes to hold the variable capacitors. I had a few dual-gang units I bought from GQRP with 60pF on one gang and 140pF on the other. I ended up using the 60pF gang from one cap on the antenna side and the 140pF from the other cap on the TX side.

Once these were mounted, as I was using a C-L-C Pi circuit I connected the two centres of each socket to the appropriate gang of the caps.

I then added the inductor, again, soldered between the two centre pins of the co-ax connectors.

Finally, I wired the earths of the capacitors to the earth tags of the coax connectors

A few tweaks of the capacitors, and both the rig and the inline meter are happy with the match.

This was with 10W of FM at 70.25MHz. The W2000 has some small capacitors in the matching section in the base, and I do not want to risk toasting them.


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