[Fwd: Snake Antenna]
Sun, 30 May 1999 11:15:07 -0400
Keith Ballinger wrote:
> In the RSGB book "Practical Wire Antennas" by John Heys G3BDQ there
> is reference to underground antennas laid in a ceramic conduit. The article
> refers to an entry in "ARRL Antenna Compendium Vol. 1" and work done by
> W0YBF on receiving WWV at 5MHz. Furthermore G6PG installed a 60ft wire
> suspended between "pan tiles" about 2.5ft below ground and with 8 watts on
> HF worked 1000 miles.
> The article continues: "At 5MHz a radio wave penetrating average
> soil is attenuated about 1.87dB per meter of depth; however there is
> relection and refraction loss. W0YBF's antenna, about 8 inches below ground,
> had an average signal loss of 16dB when compared with a half-wave dipole at
> 0.3 wavelength above ground.
> "The length of a resonant wire when buried is much shorter than a
> similar wire suspended in air. The 5MHz antenna by W0YBF had to be shortened
> from 93.6ft to only 46.6ft. The earth's dielectric properties affected
> velocity factor which was measured at 47.4% at 8 inches depth, and 25% has
> been recorded at greater depths."
> The article goes on to comment on a practical installation for "no
> antennas" restrictions and does say that receive noise would be very low.
> On the subject of radiating coax, there is indeed much work done on
> this for communications within buildings, tunnels etc. The technique is to
> use hardline coax (similar to Radiax) with one face of the corrugations
> milled off to provide a series of slots. Alternatively, two concentric
> semi-circles of screening can be used; see the Web-site
> http://www.timesmicrowave.com/products/commercial/nutrac for info. The
> advantage of radiating cable is that it can handle multiple frequencies
> through a multicoupler (eg, VHF, cellular, PCS) where several different
> services require coverage in difficult areas - underground parking, subways
> (eg TTC) etc.
> Keith VA3QF