On the funny bands it works just like Tube Shortwave said, in fact I have not been able
to hear anything above 5 megs on it aside from local CW
.
So ... numerical result data wasn't convincing?
(copied from the first response - data from chart on W8JI website at the link found in the first post)
http://www.w8ji.com/receiving.htm )
Antenna Type RDF (dB) 20-degree forward gain (dBi)
--------------- ----------- ----------------------------
1/2wl Beverage 4.52 -20.28
Vertical Omni, 60
1/4wl radials 5.05 1.9
Gee, willya look at the "forward gain" at the 20 degree incoming angle ... much signal at 20 dB down *?
Prior to seeing W8JI's chart I had not realized such a big difference existed (btw a beverage and 'sensitivity' related to elevation angle), and tend to be 'skeptical' of off-handed claims unless I can see some numerical data since there are so many old-wives -er-
ham tales out there ...
Nice to see some confirmation of what W8JI saw too
* Relative to a 0 or 1 degree elevation angleA couple of issues here.
The W8JI data quoted does not really explain why Beam Tetrode is not getting better performance, and, a pet peeve of mine, when is a Beverage a Beverage?
First, the W8JI data does not explain why Beam Tetrode is not getting the performance he should from the Beverage. The quoted numbers, for a half wave Beverage, are not applicable to the areas he is having problems with.
Beam Tetrode has a Beverage that is 80 meters long. He specifically states it works with better signal to noise than his G5RV on 160 and 80 meters but is not working well above 5 MHz. At 5 MHz the antenna is near 2 wavelengths and the 20 degree gain performance from the W8JI chart should be within 6 dB of the vertical. 6 dB is 1 or 2 S units, depending on how your radio is calibrated. 1 or 2 S units are important, don’t get me wrong, but should not equal “I have not been able to hear anything above 5 megs on it aside from local CW”.
The next section is a minor rant from me, feel free to ignore it, but I am agonna say it
A half wave Beverage just is not a Beverage, I tell ya! By the way, it is presented here for discussions sake, not arguments sake, if it comes off confrontational that is accidental.
What makes a Beverage a Beverage? The original patent (1381089, filed June 7 1921) claims that the operational affects of the Beverage start at “over” 1/2 wavelength and increases in performance from that point. More recent definitions of the length of a Beverage (and all known real-world applications of the Beverage by it’s inventor, Harold Beverage) are “more than one wavelength”. While this does not mean a Beverage or Beverage like antenna cannot be only half a wavelength it would be a strong indicator that if you want one to work, as a Beverage instead of as a random low wire, they should be “long” in relationship to the wavelength, ie, a full wave or longer.
With this in mind it becomes pretty clear why the W8JI data shows such a high main lobe for a 1/2 WL “Beverage”. A 1/2 wave antenna that is unterminated will display a main lobe somewhat perpendicular to the wire axis in free space. In close proximity to the ground the primary lobe energy towards the ground will be reflected up, adding to and remaining in plane with the perpendicular to wire axis lobe, OK, it can become somewhat more pronouncedly double lobed at this point. Terminating the wire at the far end will “bend” the lobe towards the termination. The velocity of the signal in the conductor is slower than the velocity of the signal in free space, so the longer the wire, the more the lobe will be “bent” towards the termination end.
So, a halfwave Beverage will have a high angle cone in the direction of the termination. The longer the length of the Beverage the lower the included angle of this cone, and the greater the gain in the primary lobe. At a half wave the main beam is pointed up so the gain towards the horizon, relative to a “no gain” (some verticals do have gain, lets assume none for this) omni directional vertical, is down significantly, just over 20 dB if the W8JI data is correct (and there is no reason to believe it is not). The main lobe itself of the Beverage may have more gain than the vertical (probably around 3 dB if the vertical is 1/4 wave), but it is pointed more up in relationship to the vertical.
As I said above, the longer the Beverage the more this main lobe comes down towards the horizon and, at the same time, the more gain the main lobe has. And thus the gain delta at 20 degrees between the vertical and Beverage is down to about –6 dB by the time the Beverage is 2 wavelengths long. However, the gain in the main lobe is now up around +4 dBi or more. So, the longer the better, but also the more directional.
But all of this is plotted along the wire axis. The main lobe at the horizon and some angle (angle depends on antenna length and other factors) off the axis of the wire in the horizontal plane will be many dB up from the vertical omni performance. These main lobes on the horizon still will not have as much gain as the main lobe up does, but it is closer to the theoretical.
Placement of a Beverage, or any other fixed directional antenna, is important because once placed they are going to work well in a specific direction and, by design, not so well in others. With a Beverage think about where you are placing the lobes, not just the wire axis, a long enough Beverage (say over 3 Lambda) should start to blur the lobes with the wire axis. With a Rhombic the central axis is the lobe axis.
