With that in mind let me introduce you to the hardware at Radio Arcala in Finland.
That tower is topped with two antennas (which are constructed of towers themselves): the bottom one is a three element yagi (directional antenna with gain) for 160 meters while the top is a four element yagi for 80 meters. Now, remember, the length in feet for a half wave dipole is 468/f with f in MHz. That says the elements of the antenna need to be 134 feet tip to tip for the bottom end of 80 meters and 260 feet for the bottom of 160 meters. And they need to be spread out with about 2/10 wavelengths between the elements (that number varies with the antenna design; it's very approximate to give an idea of size).
According to their website, the vital stats
- Tower height: 100 meters or 330 feet
- 80 m beam 90 m (300 ft) long
- 160 m beam 80 m (270 ft) long
- Total weight 39,600 kg (80,000 lbs)
To give you an idea of the scale up close, here's a section of the 160m antenna where one of the elements meets the boom that holds the three elements. With a prop for scale.
This is tower number 7 of 7 at Radio Arcala. All privately funded, lots of volunteer work, designed and built by a group of hams who wanted the best signal in the world on those two bands.
In the comments to that video, one says, "now collapsed due strong gust wind" dated six years ago. I guess that means it stayed up a few winters.
One of the projects Martti Laine, OH2BH, was/is involved with. I've worked him half a dozen times in contests, but never on 160 or 80. I was quite pleased when I worked him on 40 Meters from SoCal.
ReplyDeleteFor those who don't know, Martti is a Nokia Engineer, and is almost revered in the Amateur Radio world for doing things like this, along with going on, and helping to finance, DXpeditions around the world.
If you ever had a Nokia phone, and received a text message on it, you've seen his handiwork. The correct technical name for texting is "SMS", for "Short Message System", and the phone beeps three short, two long, and three short when the text comes in.
That pattern is Morse Code for the letters "SMS". The first time I heard it on a friends phone, I thought it was sending an SOS (three short, THREE long, and three short), and when I heard it beep again, I realized what it was, and asked him if he had a Nokia phone. He asked how I knew it was a Nokia, so I explained it to him.
Hams are everywhere!
All my antennas have stayed up through the Winter here in Colorado, absolute proof they're not big enough.....
This radio infrastructure is the kind of thing that would be straightforward if you weren't submissively surrendering two thirds of the wealth you produce to the District of Columbia, to be reapplied to oppress you.
ReplyDeleteI know. The brain behaviors programmed by your chimpanzee genetics say you had better obey the monkey with the best dominance display, or the sky will fall. I know, you don't have a rational counter-argument to this. You only have jumping and screaming and throwing forest litter, as expressed in text in the New York Times and the Atlantic.
DRJIM (my mentor) is guiding me in setting up a 40' long antenna at the White Wolf Mine that should stay up all winter as it is designed to be suspended between two power poles. But this...this antenna, raises the bar considerably.
ReplyDeleteI remember the day that nobody told me about the windstorm. Reception dropped to almost nothing, no matter which way I pointed the antenna. I saw the problem when I went out for lunch, as that antenna tower was next to the chow hall. The antenna was twisted and pointed at the ground. It took (some amount of time) to get that position operational again.
ReplyDeleteSuch was life in Field Station Berlin. Good times.
Do I correctly deduce that the top and bottom arrays radiate at 90* to each other?
ReplyDeleteI don't know of a way to do that with a Yagi. I'm all but sure they both radiate in the same direction.
DeleteIf you're thinking that because of those small sections at right angles to the elements at the ends (on the lower one), I believe that's an end loading fix for an antenna that's a bit short, like a capacitive hat, except those tend to be larger.
http://www.arrl.org/news/storm-takes-down-amateur-radio-contest-club-towers-in-northern-europe
ReplyDelete"about 2/10 wavelengths" Dumb question..If the wavelength was 10' then separation would be 2'? I'm confused by the fraction you used, thinking it should be 1/2 wavelength. Keith.
ReplyDeleteNo, you're right the first time - if the wavelength was 10', it would be 2' between elements. This antenna (the bottom one) is for a wavelength of 160 meters. 0.2 * 160 is 32 meters. The boom is 80 meters long and 32 is about 4/10 of 80 meters, and it looks like it's approximately 40% of the length of the boom away.
DeleteBut like I said, that's a crude approximation. How a Yagi works is the middle element is driven. Some of the signal radiates backwards and is reflected back forward by the rear element (which is called the reflector). If it's 1/4 wave (0.25) back to the reflector, then when it gets back to the driven element, it has shifted 1/2 wave in time (1/4 wave to what's called the reflector and 1/4 wave back). Here, it adds constructively to the part of the signal going forward. The element in front of the driven element is called the director and it does something similar, bouncing some signal back toward the driven element and reflector and that signal combines, too.
Edit to add:
DeleteThere's lots of descriptions of how yagis work; some are better than others. I first learned about them from an ARRL publication. This treatment seems pretty good. It's important to know that designs vary depending on what they're optimized for: gain, bandwidth, front to back, or front to side ratios. There are some standard designs, from the National Bureau of Standards and every company that makes them has their own ideas of the best design trades. There are open source software packages you can use to design one.
Thank you. The link helps. I'll study it...Keith GBY
ReplyDeleteEver been to an "Elephant Cage"? I put three 9M dishes in right down the road from the one in Guam.
ReplyDeleteNo, I haven't seen those. Interesting rabbit hole to go down!
DeleteI gather one or two are still operational, but are mostly gone.