I recently built a EFHW UNUN from a K6ARK kit (and I asked about the capacitor I broke in another post). I hooked it to a NanoVNA and a 2.2k carbon film resistor, swept 3 to 30 MHz, expecting to see a flat SWR. Instead, the SWR was about 1.5 at 3 MHz and rose a lot - to over 8 - at the higher frequencies. I repeated the measurements with three other UNUNs from kits - one K6ARK and two KM4CFT. (These three all have their capacitors intact.) All exhibited roughly the same behavior. What am I missing?
Just as a sanity check, I hooked a 50 ohm QRP dummy load to the NanoVNA, and it behaved roughly as expected - SWR 1.0 at 3 MHz and about 1.5 at 30 MHz.
thanks, geoff, N3CFX
EFHW UNUN test
Re: EFHW UNUN test
Maybe connect the dummy load to the output of the unun and try again? It won't have a 1:1 match, but you'd see if the SWR remains constant over the range.
How does the unun do with an actual wire attached? And did you find a capacitor or not?
73,
Mike, KL7MJ
How does the unun do with an actual wire attached? And did you find a capacitor or not?
73,
Mike, KL7MJ
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Andrew (grayhat)
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