Pieter-Tjerk de Boer, PA3FWM? has a series of articles on E-Field antennas that can be extremely helpful in getting the best performance from these antennas.
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Fundamentals of the MiniWhip antenna
https://www.pa3fwm.nl/technotes/tn07.html
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Grounding of MiniWhip and other active whip antennas
https://www.pa3fwm.nl/technotes/tn09d.html
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[Note it is critical to properly ground the E-Field antenna at the antenna and to isolate the coaxial cable feedline from EMI generated within your home!]
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Simple and better circuit for MiniWhip antennas
https://www.pa3fwm.nl/projects/miniwhip/
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Martin G8JNJ had a very informative web page on active antennas. His use of high inductance RF chokes in the feedline is an extremely useful technique to isolate the ative antenna from EMI generated in the home. Sadly his webpage has vanished but a PDF capture of the webpage can be found at
https://qsl.net/l/lw7dfm/Antenas/Antena%20Mini%20Whip/MARTIN%20-%20G8JNJ%20-%20Active%20antennas.pdf
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His webpage is archived on the "wayback machine" but it won't always load.
https://web.archive.org/web/20230722120107/https://www.g8jnj.net/activeantennas.htm
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I use quad shielded 75 ohm flooded coaxial cable to connect to my E-Field antennas. Assuming my Kenwood R-2000 receiver has an actual antenna input impedance of 50 ohms, exceptionally unlikely, the worst case VSWR would be 1.5:1.
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The SDRplay RSP-dx has a claimed input impedance of 50 ohms over it's entire operational range. I have no reason to doubt this but no way to verify it either. Reception was so similar with the 75 ohm and 50 ohm coaxial cable I couldn't tell any difference and 75 ohm flooded (rated for direct burial) cable is a lot easier for me to obtain here in central Kentucky. The son of a member of our shortwave listening club is an engineer for the local cable TV company and can divert reasonable lengths of coax. I also have 7/8 hardline for the two antennas located the farthest from our home.
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I just connected a Radio Shack Disk Cone antenna (at least 40 years old now) to my RSP-dx and I can receive all of the NOAA VHF WX stations within 150 miles. There are more commercial FM BCB stations then I can count and I can receive a 2M amateur repeater that I know runs 50W that is located just over 100 miles from my home. Constructing a decent disk cone isn't that challenging but Diamond and others offer them for reasonable prices, so it becomes, do I want to trade money for time.
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