Is this homebrew worth it?

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cassidy1190

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I just read the post in the listener forum on Liveatc.net "Airband Yagi antenna designs" at Airband Yagi antenna designs | LiveATC.net.

I am very intrigued by this, and have made yagis before, but for 800-900MHz. I have yet to try one set up for airband VHF.

I am wondering if what I am trying to do will even be worth my efforts. I live on the jersey shore, very close to the ocean (1 block) and would like to try and pick up JFK tower, app and dep. Do you think I would be able to here the controllers from where I am located with this antenna pointed at JFK? Has anyone else had luck with it before? I really appreciate your input.

Attached is a NY sectional chart of where I am in relation to JFK, approx 30 miles southwest.
 

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ka3jjz

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Maybe, given sufficient height of the antenna, which is the one factor in your description you didn't mention. You may, in fact, find that your range extends further than that, depending on the terrain that surrounds you, but at 30 miles, and with that path - your chances would increase considerably if you were to build a yagi that you could put outside, rather than a printed circuit board one....73 Mike
 
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kb2vxa

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Receiving ground based VHF air comms has always been difficult at best because they're designed for ground to air, not ground to ground which is limited to aircraft movements at the field. It all comes down to 10W transmitters, simple ground plane or discone antennas and the control tower being only high enough to give a clear view of the field. You MAY receive the NY area towers with a BMF beam up really high but there is no guarantee shooting at Queens NY with the eastern slope of Telegraph Hill and Mount Mitchell in the way. (Look again at the map, the path barely skirts the highest point on the Eastern Seaboard.) Being on the shoreline and just a tad south of you I never had the best of luck hitting western Long Island while we have a pipeline farther to the east, reflections off the mountains causes multipath reception which plays hob with the signals close in while having no effect farther out.

I don't mean to discourage you, just telling it like it is. Rather I'm encouraging you and so many others to experiment thus furthering the hobby beyond the bounds of plug 'n play. Hey, what have you got to lose?
 
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Chances are the actual approach and departure radio sites are not located at the airport but they could be located several miles away. FAA usually uses remote separate transmitting and receiving sites, a common configuration is a site with 4 relatively short 4 leg towers (that remind you of an old windmill tower) in a square with an equipment building in the center of the square, they co locate the associated transmitters at one site and receivers at another.
 

cassidy1190

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I would think at least the tower transmitter is actually located at the tower. Other than that (app, dep, centrs) who knows. Yeah I hear ya kb2vxa, if anything I'll just have fun building it. Im using 1-1/2" X 1-1/2" wood boom and 1/2" copper pipe for the 3 elements.

EDIT: Attacthed are the actual designs of the antenna. I didn't realize you couldn't see them on liveatc if your not a member.
 

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nanZor

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Be sure to bring the coax straight past the reflector for minimal interaction. If you have to drop the coax down between the elements, drop it half-way between two of the elements, and not right next to one. As an additional precaution, I'd place about two or four RF chokes at the feedpoint - the Radio Shack type-43 #273-105's should do.

The article points out that the spacing used is optimum for 50 ohms. If you are using 75-ohm RG-6 for example, you may want to space the elements further away from the driven element ending up with a wide-spaced beam more suitable for 75 ohms.

Before drilling anything in stone, make sure you can move the elements back and forth to find the best point. If your radio has an S-meter, so much the better!
 

cassidy1190

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Right now I am using a homade dipole tuned for 120 mhz. I am in fact using RG-6, so I have the coax hooked up to the antenna feed point with a 4:1 balun. Could I use a 4:1 balun on the yagi too, instead of playing around with the spacing of the elements? All I have is 75 ohm RG-6, lots and lots of it.
 

Uplink

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Mine works, it's made out of 1/2" PVC, and steel welding rods from Home Depot. I made a 5 element version with 75 ohm spacing and 50' of RG6-quad satellite coax. I am getting Burbank Tower and Approach from 27 miles away. It's in the attic, on a PRO-136 (very good aircraft receiver) and I have about 400' of elevation higher than the airport, however I do have some terrain in the way. ATC Towers are very weak and difficult to get, usually the transmitters aren't even on the tower itself, they are down low or on a very small tower somewhere else on the field.

Can you get the Hudson River VFR corridor traffic on 123.075 and 123.050?
There has been much speculation and reports about comms used or misued on those freqs, and the FAA made changes in rules after the recent crash, but unfortunately NOBODY is streaming those freqs on LIVEATC.NET! Every OTHER dang JFK freq is streamed except those. It's a busy area and you could fill an interesting niche if your in range. Just a thought. :D
 

Citywide173

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Looking at the pics, I have to ask....shouldn't the orientation be horizontal rather than vertical for AM?
 

kruser

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Looking at the pics, I have to ask....shouldn't the orientation be horizontal rather than vertical for AM?
No, the type of modulation (AM/FM) makes no difference. The polarization of the transmitting antenna is the determining factor. The receiving antenna should match the transmitting antenna and AFAIK, aircraft comms mostly use vertical polarization.
 

Citywide173

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No, the type of modulation (AM/FM) makes no difference. The polarization of the transmitting antenna is the determining factor. The receiving antenna should match the transmitting antenna and AFAIK, aircraft comms mostly use vertical polarization.
That makes sense.....I remember being told at one point vertical was for FM and Horizontal for AM (by a superior at the radio shop I worked at) and it stuck with me, but thinking about it, TV antennas are usually horizontally mounted, and that's FM.
 

prcguy

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If your dipole is a half wave and about 50" total in length then loose the 4:1 balun, the antenna will have a good match to TV coax.
prcguy

Right now I am using a homade dipole tuned for 120 mhz. I am in fact using RG-6, so I have the coax hooked up to the antenna feed point with a 4:1 balun. Could I use a 4:1 balun on the yagi too, instead of playing around with the spacing of the elements? All I have is 75 ohm RG-6, lots and lots of it.
 

cassidy1190

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Mine works, it's made out of 1/2" PVC, and steel welding rods from Home Depot. I made a 5 element version with 75 ohm spacing and 50' of RG6-quad satellite coax.
How do you figure out spacing for 75 ohm?

If your dipole is a half wave and about 50" total in length then loose the 4:1 balun, the antenna will have a good match to TV coax.
prcguy
Even if the coax is 75 ohm?
 

nanZor

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Programs like EZNEC can help figure out the spacing. However, when you do that you also have to take into account overall gain, front-to-back, swr bandwidth etc.

Problem is, you are drastically changing the gameplan by using 1/2 tubing, rather than thin wire stock.

Definitely drop the balun - not needed as a dipole is 73 ohms and the RG-6 is very close to that. The balun in this case is not helping. Who knows, you might not need the beam after all. :)

(The balun/transformer would only be necessary if your dipole was a folded-dipole built with twinlead)

Unless you have an outrageously lossy run of feedline, I'd build per the article and see if you can live with it - even with the mismatch.

If you use the thin wire, try the two-element version first as this gives you the most bang for your buck. Try moving the reflector away a few inches at a time, up to about double the dimension shown and see if there is any improvement. If you get that working, add the director.

Perhaps someone more skilled than me with EZnec could design a nice 7db or so 3-element beam made from 1/2 tubing. I tried, but quickly found out that designing beam antennas will never be my day-job. :)
 
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cassidy1190

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Well I am definitely excited to try out my dipole without the balun now, but I am a little confused about the beam. What is different about using 1/2" tubing?
 

cassidy1190

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my only issue with this is that copper tubing is the only material I know of thats easy to find that is sold in long lengths. The brasing rods which are common for yagi making, and much thiner, are usually sold in shorter lengths, so I would have to splice them in the middle. To me that just leaves extra room for error.
 

davidmc36

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The brasing rods are usually sold in shorter lengths, so I would have to splice them in the middle.
Do they come in four ft lengths? If not you should be able to get piano wire in 4ft. I cover it with heatshrink though to keep it from rusting. Stainless is more pricey. You would only have to splice the reflector etc at the boom. Should be easy to attach them solid there.

Edit: Second look I see the total length of the reflector is 48" so no splicing would be needed with 4ft wire.
 
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