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Title: Johnson Matchbox Post by: W4AMV on November 02, 2021, 02:19:47 PM Picked up a Johnson Matchbox saved from scrap. Cleaned up well. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
I checked the balanced line match on 80 meters and a 4.3 k termination could easily match down to better than 30 dB return loss. On 40 meters, a 2.2 k matched down to better than 35 dB return loss. So the spec in the manual seems very conservative. Has anyone fully characterized this tuner? I could run some loads around the SWR circles but if already done, great! I have not checked the single end wire feed point match ability or how low a Z might be accommodated. I did some additional testing for low Z. Also extended high Z to 2.7 k and no problem. Very good at better than 20 dB return loss. The low Z side is a different story. It appears that the matchbox sweet range is to the right of the 50 ohm circle. That is 200 ohms, 75 ohms and so on. Just don't drift to the other side of the circle! No match below 25 ohms or just a 2:1 SWR. Maybe one has to play with the link a bit. 73' Alan |