Michael, You have several factors with a dipole vs. vertical: 1. Noise tends to be vertically polarized. Thus a vertical antenna is in the incident wave of noise sources and couples more readily. 2. People tend to think of the dirt and ³ground² as if the soil were the bottom of a metal box. We drive a ground rod into the earth and proclaim that we are GROUNDED as if this was some virtuous experience. Soil is, at best, like a big, spongy resistor. We do our best to provide a reference for the radiator in a vertical to work against and we do this with ground rods and radials. The desired effect is to only reduce the RF impedance of whatever ground we got. 3. The dipole works against itself. The E-field (electric) flows along the wire and is 180 degrees out of phase at the center where we put our feed point (in most cases). At 90 degrees is the M-field (magnetic). These loop through the air back to each-other as a big bubble of energy. The vertical has a more difficult time of doing this because of variations in the counterpoise. 4. The dipole is further aided by very high Q or ³quality² by virtue of the wires. The ratio of the wire diameter to the wavelength is very, very small especially on 80 meters. Because of this, the antenna is not as broad-banded as most verticals tend to be. So, you¹ve set up a much better antenna with higher Q and put it 90 degrees out of the plane of the (most) noise sources :)
73! Bill Crowell, N4HPG Pearland, TX Text messaging one-handed since 1982 From: BVARC <[email protected]> on behalf of BVARC <[email protected]> Reply-To: BVARC <[email protected]> Date: Monday, January 11, 2016 at 9:51 AM To: BVARC <[email protected]> Cc: Michael Rapp <[email protected]> Subject: [BVARC] Why is my dipole quieter than my vertical? Hey all, Now that I have multiple antennas up, it is interesting to compare them. For nearly four years now, my wire vertical (30 radials) has been my workhorse antenna. This past July I also put up an inverted-V multi-band dipole, cut for 80 meters and fed with 450 ohm line. The apex is about 20 feet up. One thing that I've noticed is that, especially on 20 meters, my dipole is quieter than my vertical (which is cut for that band). When I say quieter I mean that when using an A-B switch the volume of the background noise is quieter on the dipole. I began to wonder is it just the noise or is it the noise and the signals being attenuated on the dipole? With the little equipment and knowledge that I have, doing an objective test is challenging. I've been using JT65 as it gives fairly objective signal reports. Being very careful to keep the net sound card level input the same between antennas, it appears that for domestic signals on the dipole I can consistently decode down to about -27 dB whereas on the vertical I seem to be only able to consistently decode down to -22 dB. This seems to suggest that the signal-to-noise ratio of the dipole is better than that of the vertical, which suggests that the dipole is less sensitive to noise -- unwanted signals -- than the vertical. Why would this be? What I've been able to research/Google has been confusing. Some suggest that it is because most noise sources are vertical polarized. (Are they?) Others suggest that because half of my vertical antenna is in the ground (the radials) this does...something... to make it more susceptible to noise. And others point to the dipole having a little bit of directivity contributing to its nulling out, probably by coincidence, some of my noise sources. 73, -- /*/-=[Michael / KT5MR]-=/*/ _______________________________________________ BVARC mailing list [email protected] http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org
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