XPost: rec.radio.amateur.moderated
LA3ZA Radio & Electronics
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Reversing the inductor in the Chinese QRP antenna tuner makes all the difference
Posted: 23 Jun 2022 03:16 AM PDT
https://la3za.blogspot.com/2022/06/reversing-inductor-on-chinese-qrp.html
Like many I was disappointed with the Chinese antenna tuner kit "QRP manual days" back in 2014 and I never really got it to work.
That was even after I had replaced the two polyvaricon capacitors. The two screws for mounting each of the variable capacitors were too long. The
result was that they interfered with the moving plates of the capacitor and
I ruined both of them. There was no warning of this in the manual, so
beware anyone who buys this kit.
Despite fixing this, it didn't really tune anything. I later learned that
it probably works for low bands like 80 m as it is, but I didn't notice
that. I thought maybe the inductor was of inferior quality, but never
really investigated it, so it sat unused on the shelf for 7-8 years.
Recently, however I learnt that there is an error in the instructions which makes all the difference: The inductor should be reversed. In this way, one
can get the small inductance value consisting of only a single turn at
position A of the rotary switch. Prior to this fix, the inductor starts
with 10 turns at position A, and this is too much except for the lower
bands like 80m.
This is spelled out in this video by KP4MD, Carol, from 7 July 2021
starting from about 10:00 minutes. The particular frame that shows this is reproduced here also.
What I did was to desolder all 12 or so connections from the inductor to
the rotary switch - be careful not to melt the plastic around the switch contacts. I actually did that and had to disassemble it in order to get it
back in working order. The I unwound the wire from the toroid core and
rewound it in the opposite direction. And then resoldered it back.
That made the trick, now it tunes 20 m also!
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