If I am Tx'ing a VHF GrndWave of how much value is a Beam Antenna?
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| Jan 6th 2014, 16:54 | |
xof7foxTotal Topics: 0 Total Posts: 0 |
I am struggling to understand the value of a Beam Antenna for 2 Meters IF I am Transmitting an FM Vertically Polarized Groundwave. And, in advance, I thank you for taking the time to read this Post and, further, trying to advise me if you can. HERE IS MY QUESTION: Does a Beam/Directional help me push the FM Groundwave past the otherwise LOS limitation by some anticipate-able % greater amount? Meanwhile, with regard to all of the above I do understand that: 1. A Beam will help me Receive (this Q is exclusively about Transmitting). 2. If I am going after a bounce off of Meter/or 'equivalent' Scatter, or making it to a satellite or the space station then the Beam adds to my effective Transmit distance.(this Q is exclusively about Groundwave/LOS, not Skywave). MANY thanks, Fred k4xxk. |
| Jan 6th 2014, 19:43 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
Yes, a beam can help. NC1I has a 48x15 element array on 70 cm FM that can be used to get all the way into NYC from Massachusetts! The trick is that his huge 720 element array has polarity rotation, as well as azimuth and elevation control--very few hams have all three! As a rule of thumb, improvements are quite difficult until your station has a range of 100 miles--but once you get to that level, additional improvements can easily get you to 250 miles, where it gets hard again. Most FM stations aren't anywhere close to having 100 mile typical range--they can only hear the occasional repeater in which the other station is doing all the work. For many hams, getting a beam just isn't worthwhile since it has to be pointed accurately to get the theoretical benefit. Zack Lau W1VT ARRL Senior Lab Engineer |
| Jan 6th 2014, 23:18 | |
aa6eTotal Topics: 0 Total Posts: 0 |
Yes a beam is a good thing. Of course, there are downsides: they can be moderately expensive, they have to be pointed (fixed or rotatable), etc. And you want height, which helps for any antenna - up to 30 ft or so for 2 meters. A 4-element beam might give you 10 dB of gain. That's like increasing your transmitter power by 10 and increasing the other guy's power by 10. Naturally, you will get a greater communications range -- in the direction the antenna is pointing. In free space, doubling the distance cuts power by a factor of 4 -- about 6 dB. So your beam should more than double your range. Well, maybe not, once you consider the curvature of the earth and other complications. Still, it's generally a good thing. If you really want maximum range on VHF ground wave, you might check out SSB. It performs much better than FM for weak signals. (CW is even better!) With my not too fancy SSB setup (10 element beam, 50 watts), I can work out to 120 miles or more. With a simple antenna, you may find that you can use a bunch of repeaters, but people will say you signal is noisy -- not full quieting. With a beam, your signal should be boosted to full quieting, and everybody will be happier. For really long distance repeater-like communications -- well, you can try EchoLink or D-STAR. (Internet linked systems) 73 Martin AA6E |
| Jan 14th 2014, 23:56 | |
xof7foxTotal Topics: 0 Total Posts: 0 |
Thank you Zack. Thank you Martin. - Fred K4XXK. |
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