Short Wave Antenna4/26/2021
Normally, a passive counterpoise is a quarter wavelength of insulated copper wire connected, in your case, to the receivers ground post.The description he gave of his installation revealed several shortcomings that could easily be remedied by.Here are the possible solutions for each shortcoming that his attic shortwave antenna installation presents, along with the recommendations I made to him.Bare copper antenna wire stapled directly on wood rafters causes loss of RF signal energy.
With time, bare copper oxidizes.The wood, where the wire is tightly stapled to, absorbs some of this oxidization and forms a loose yet lossy bond with the wire. The staples themselves dig into the wood and further increase the bond. Remove staples. Instead, staple a closed tie wrap (forming a loop) at each stapling point. Run the wire through the loops and let it hang slightly away from the wooden rafters. Insulate the wire with electrical insulating tape where the bare wire might come in contact with wood or any other foreign object. Or. replace the oxidized bare copper wire with insulated copper wire. Then, run the wire through tie wrap loops as above, slightly away from the rafters. It can potentially capture and contaminate the valid RF energy - coming in from your attic shortwave antenna - with undesirable electromagnetic and electrostatic interference. This interference is not being dissipated into a proper load because the coax shield is not terminated at both ends As a result, the unwanted interference causes the background noise to increase in the receiver, thus reducing the signal to noise ratio. ![]() It might prove to be enough to prevent the floating coax shield from acting as an antenna. On the other hand, you will never know if you are shortchanging yourself. That would make your end-fed antenna 150 feet long which is not a problem in itself. ![]() The near vertical portion of wire (20 ft) from the attic shortwave antenna to the receiver could pick up vertically polarized electrostatic interference. Install a 9:1 UNUN at the antenna end of the coax. UNUN stands for unbalanced coaxial line to unbalanced antenna). You should then make the coax shield connect properly to the PL-259 connectors at each end. The coax shield would then be properly terminated at both ends and stop being a rogue antenna. You could opt for a commercially made 9:1 UNUN or build a homemade one like I did. A L-network is the best impedance transforming configuration for end-fed antennas. Stay away from lossy T-network configurations). This is a length of wire that is added to simulate the presence of a good RF ground right at the receiver - when no good ground is available (like a water pipe) which is generally the case for those who live in an apartment building.
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