Comms: Where are we now?

[Lightspeed]

(28 June 2013, 11:29)Tarrel Wrote:

(28 June 2013, 09:38)Highlander Wrote:

(27 June 2013, 23:16)Tarrel Wrote: Or, use a simple long wire, again mounted close to ground, and connect to radio via an antenna tuner. It is the closeness to the ground that makes it NVIS.

I was lead to believe that to have the antenna too close to the ground would not give good results, because of the fluctuation of the wetness in the ground

If that's a problem, you could bury a layer of chicken wire or similar in the ground beneath the antenna, to provide a more reliable earth. Opinions vary about how low to the ground an NVIS antenna needs to be. General view seems to be around 1/8 wavelength or less.

Agreed. The generally accepted concept is that NVIS Antennas must be horizontal, and around 1/8 wavelength or less above the ground. The NVIS technique uses the ground to reflect transmitted signal Nearly Vertical.

So:-
For 3.5Mhz band (80m) antenna should be less than 10m (30ft) from the ground
For 7Mhz band ( 40m) antenna should be less than 5m (15ft) from the ground

This means that for most ground conditions,3.5Mhz and 7Mhz antennas less than 3m (15ft) off the deck will perform well for NVIS

HL I agree with you that getting the antenna too close to the ground may introduce problems as well as making it a trip hazard. I've found that mounting an end fed wire along the top of 6ft to 8ft WOODEN fence posts works pretty well and is very inconspicuous. The wire can follow the fence line around boundaries, it does not have to be straight at all, as long as it is approximately horizontal.