Comparing my past hand calculated numbers vs. those obtained via EZNEC shows that the two numbers closely agree in improvement difference when comparing real antennas. There is a bit of a difference when comparing to an isotropic antenna due to my compromising on the number of high elevation angles used in my manual calculations. The numbers below are those obtained via EZNEC software. The figures obtained this way agree very closely with what I have observed with actual antenna use comparisons.
The numbers below were trying to show three things:
The noise reduction due to using different Beverage antenna lengths.
The noise reduction due to using a different number of phased Beverages.
The noise reduction improvement by using a loaded uni-directional Beverage vs. and unloaded
First the obvious: Noise (static) rarely if ever comes equally from all azimuths and elevations. If the noise is coming from something close to a point source then designing an antenna with a null in the appropriate direction will be a much better solution. But, in places like this one the noise comes from a wide azimuth range with a changing heading. Finding an antenna with the greatest average relative noise reduction provides a better overall benefit here in the long term as compared to reducing the noise from only one direction.
Comparing some common 160M antennas and ones which I have personally built and used produces the following results:
RELATIVE ANTENNA NOISE COMMENTS Isotropic ant 0 dB 2 ele vert -8.12 Classic 90ºspace/90ºphase array for comparison My xmit ant -10.61 537.5 Bev -10.57 280 ohm load 537.5 Bev -7.41 Not loaded 580' Bev -10.60 360 ohm Load 580' Bev -7.50 Not loaded 881' Bev -12.20 390 ohm load 780' Bev -11.85 330 ohm load 2 x 780' Bev -11.96 6' spacing, no stagger 2 x 780' Bev -13.56 6' spacing, 1/4 wave stagger feed/phase 2 x 780' Bev -13.84 350' spacing, no stagger 3 x 881' Bev -15.36The single Beverage loads above were chosen for the best relative noise, not front to back. A compromise load value choice is often the best. The 3 phased Beverage figure is based on an example which I have actually built and used where minimum relative noise was not the only factor used in antenna design. My personal tests and use experience confirm the relative validity of these numbers. The calculations and personal use has shown that the high ground conductivity here decreases Beverage dBi signal levels a significant amount. The relative receive noise figures go down just a bit with the higher conductivity as well. And, I have tried unloaded Beverages and have always found them to be of almost no value (compared to other antennas available). Besides the above figures, on days when the noise (or QRM) is towards the back of the antenna, the relative noise improvement of a loaded Beverage as compared to a loaded one is more like 20 dB. A reversable two wire Beverage is a better choice if both directions are desired.
The figures below I thought might be a handy reference for some. They were calculated some time ago (before EZNEC) when I was designing a phased almost-parallel Beverage array. They were adjusted to match the above EZNEC numbers. This was the first time that I was using a relative noise figure to help design such an array. While heavy on the numbers, I think that observing the progression of changing one parameter (the phase of one Beverage) is useful in that it shows a variety of things happening with my Beverage array:
RELATIVE PHASE NOISE AZ dBi BW F/B EL ELBW COMMENTS 0 -14.08 40 -8.16 54.3 24.97 24 41.6 Prior listed # 25 -14.21 46 -8.47 52.8 26.86 22 40.5 50 -14.35 49 -9.07 50.7 28.25 21 39.5 75 -14.51 52 -9.99 48.2 29.60 20 38.2 90 -14.60 53 -10.59 46.8 28.35 19 37.3 Chosen design 100 -14.62 55 -11.26 45.5 28.70 18 36.0 125 -14.45 58 -13.03 43.1 26.06 17 34.7 150 -13.43 60 -15.29 44.9 22.21 16 32.9AZ = Center of azimuth lobe
Note that while the Beverages all stay with a 40 degree azimuth, the main lobe shifts clockwise by increasing the phase delay to one Beverage. Being able to adjust the phase of that Beverage (via a MFJ-1026) can be very useful! Looking at the pattern, as my receive noise figure improved, I wasn't expecting a "less clean" looking pattern. However, the decrease in the main lobe width obviously made up for that. Also apparent was the lack of validity in only being concerned with the main lobe width figure. Using this and later phased Beverage arrays has shown that it takes some time to familiarize yourself with the action caused by MFJ-1026 control adjustment. However, once that's done, I've been able to note propagation path changes when there's a different control setting required for best reception.
For more information on this "relative receive noise" figure, see W8JI's site covering Receiving Basics and Receiving Antenna Design: W8JI RDF
If your are interested in the origination of the "relative receive noise" parameter/RDF, please review the following:
W8JI had nothing to do with its first use. First, see Tom's comment below from the following message: http://lists.contesting.com/archives//html/Topband/2000-10/msg00108.html
I previously addressed this over a year earlier, initially: http://lists.contesting.com/archives//html/Topband/1999-09/msg00123.html
I responded to W8JI's email quoting part of that second message: http://lists.contesting.com/archives//html/Topband/2000-10/msg00117.html
The K6SE reaction to my information is at: http://lists.contesting.com/archives//html/Topband/2000-10/msg00134.html
I had been quietly using my receive antenna figure of merit in the analysis of my three almost parallel Beverage array and my three element parasitic vertical array for over a year while confirming its validity before I mentioned it on the Topband reflector.
I commented about my prior email to W7EL suggesting that he included my figure in his next revision of EZNEC in the following: http://lists.contesting.com/archives//html/Topband/2000-10/msg00137.html
The above shows that I documented the RDF figure using both true root-sum-square "average" gain and the average gain outside of the antenna's main lobe way before W8JI started experimenting with it. He might be able to claim coming up with a nice name for my parameter.
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