Chicken wire
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Yes, I've heard it being done: used as a ground-plane on either the attic floor (with an attic-mounted antenna) or under the roof itself with a roof-mounted antenna. I've heard that it works, but since I haven't done it myself I don't have any first-hand experience with it.
I’ve used chicken wire, steel window screen, and more for ground plane on the underside of fiberglass and plastic roofs on various vehicles.
You just need to ensure that the antenna mount has a good contact with the material.
You just need to ensure that the antenna mount has a good contact with the material.
prcguy
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Chicken wire in general makes an excellent ground plane and it can be much more effective than wires. I have not specifically used it under an NVIS antenna but there are some things to know about what you put under an NVIS antenna.
How high will your NVIS antenna be above the roof and chicken wire? A horizontal antenna, dipole, end fed, OCFD, etc, will have the most gain and performance at around 1/4 wavelength above ground or a good reflector and thats about 32ft on 40m. Put it lower and it will reject more low angle stuff coming in but it will also degrade performance and reducing the effectiveness of your transmitted signal. Every roof is different where some are fairly RF transparent and others are sheet metal and a perfect reflector. An RF transparent roof would rely on things below it to reflect the wave upwards for NVIS like wiring, air conditioning ducts, foil backed insulation, etc. Without any of that it might have to rely on the actual earth beneath the building to reflect the wave upward for NVIS. You should probably have something reflective on the roof under the antenna to make sure it has the NVIS propagation you are looking for.
I've done lots of NVIS testing using a 5w radio on 40 and 80m with a modified military AS-2279 cut for 40 and 80m. Starting at the stock height of 15ft and lowering in, my transmit signal takes a dive on both bands. Going from 15ft to 30ft, which is a new standard for this antenna, raised my signal about 6dB average over the 15ft height. This is with the antenna above ground an no metal under the antenna but a roof mounted antenna with a reflector under it would have similar results using the same heights.
To finally sort of answer your question, in my opinion, placing a long length of chicken wire like 4ft wide and longer than the antenna on the ground or roof under the antenna, should work better than a single wire as a reflector. I have not tried this and its just my opinion. But I do know if you completely cover the area under the antenna with chicken wire like 1/2 wavelength or more wide at your lowest frequency and way beyond the ends of the antenna you will make a reflector that should work consistent and with better NVIS performance under all conditions because its not resonant and just a pure reflector surface or ground plane.
How high will your NVIS antenna be above the roof and chicken wire? A horizontal antenna, dipole, end fed, OCFD, etc, will have the most gain and performance at around 1/4 wavelength above ground or a good reflector and thats about 32ft on 40m. Put it lower and it will reject more low angle stuff coming in but it will also degrade performance and reducing the effectiveness of your transmitted signal. Every roof is different where some are fairly RF transparent and others are sheet metal and a perfect reflector. An RF transparent roof would rely on things below it to reflect the wave upwards for NVIS like wiring, air conditioning ducts, foil backed insulation, etc. Without any of that it might have to rely on the actual earth beneath the building to reflect the wave upward for NVIS. You should probably have something reflective on the roof under the antenna to make sure it has the NVIS propagation you are looking for.
I've done lots of NVIS testing using a 5w radio on 40 and 80m with a modified military AS-2279 cut for 40 and 80m. Starting at the stock height of 15ft and lowering in, my transmit signal takes a dive on both bands. Going from 15ft to 30ft, which is a new standard for this antenna, raised my signal about 6dB average over the 15ft height. This is with the antenna above ground an no metal under the antenna but a roof mounted antenna with a reflector under it would have similar results using the same heights.
To finally sort of answer your question, in my opinion, placing a long length of chicken wire like 4ft wide and longer than the antenna on the ground or roof under the antenna, should work better than a single wire as a reflector. I have not tried this and its just my opinion. But I do know if you completely cover the area under the antenna with chicken wire like 1/2 wavelength or more wide at your lowest frequency and way beyond the ends of the antenna you will make a reflector that should work consistent and with better NVIS performance under all conditions because its not resonant and just a pure reflector surface or ground plane.
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