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$\begingroup$ Why not just connect one port of the the NanoVNA to the two antennas, and measure S21 over the range of likely VUHF transmit frequencies. 50 W is 47 dBm so you need S21 to be <-47 dB which is within the dynamic range of a NanoVNA. I agree about the LPF, that's good practice. And about the unpredictability, you can't have the EFHW blowing in the wind later. $\endgroup$tomnexus– tomnexus2025-12-06 03:12:49 +00:00Commented Dec 6, 2025 at 3:12
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2$\begingroup$ @tomnexus The receive antenna will pick up strong broadcast and other signals besides the signal from the VNA and the measurement dynamic range and the noise floor will be impacted. That technique may work in some cases but I would not trust it unless verified by more reliable means.. and in that case may not provide useful info in this scenario where the quantity needed is simply |S21| only. $\endgroup$Ryuji AB1WX– Ryuji AB1WX2025-12-06 03:39:39 +00:00Commented Dec 6, 2025 at 3:39
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$\begingroup$ “lousy” -> “lossy”? $\endgroup$Jon Custer– Jon Custer2025-12-06 20:11:05 +00:00Commented Dec 6, 2025 at 20:11
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$\begingroup$ 49:1 transformers have a poor match, a transformation ratio deviation, and increased loss at higher frequencies. $\endgroup$Ryuji AB1WX– Ryuji AB1WX2025-12-07 01:53:35 +00:00Commented Dec 7, 2025 at 1:53
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$\begingroup$ Thanks for all your input. I will try an insertion loss measurement with the nanoVNA, but more out of interest than as a hard and fast solution. The LPF seems like the best solution for me. $\endgroup$Guy– Guy2025-12-08 10:22:26 +00:00Commented Dec 8, 2025 at 10:22
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