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Air Traffic Monitoring => Feed Setup Pictures => Topic started by: Chadan on June 26, 2011, 04:01:35 PM

Title: KAMW feed setup and home-built SO-239 antenna
Post by: Chadan on June 26, 2011, 04:01:35 PM
KAMW has been online for one month! Celebrating the anniversary with some pics.

The receiver is a LLOYD'S Solid State model 9N24B-37A
Both built-in antennas were slightly damaged when I received it but it is working ok after minor repairs. Most ground and air at 122.7 for KAMW's UNICOM come in pretty clear. Being an analog tuner it is less selective than your digital receiver and picks up a small range of frequencies. Sometimes included is overhead traffic for these neighboring airports:
KBNW - 123.0 (14 miles west)
KIKV - 122.9 (20 miles south)

The current feed uses the above scanner with its built-in 5' antenna. I also have a hand-held Radio Shack Pro-97 that I'll splice in when I'm performing surgery on the Lloyd's. Its 6.5" rubber whip-style antenna does a pretty comparable job to the 5-footer on the Lloyd's.

I got interested by a few ( links ( online ( and decided to try my hand at building a $20 SO-239 antenna. Well, I think I'm in over $60 now and am at a point where I'm wondering how I can tune the thing. I haven't trimmed either the antenna or the ground-planes yet. Just did a rough calculation using this calculator ( to make a 5/8 wave antenna which came out to about 4' 9 and 1/4". The ground-planes are just 36".

The main problem I face is that when I plug the antenna into the AM external antenna jack it doesn't make much difference in the reception. The 5' built-in telescoping antenna seems to work better than this custom-built one does. So all-in-all it's been a little disappointing.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Squawk 7700 on August 01, 2011, 12:54:11 AM
Chadan - Glad I inspired you to make a DIY antenna. :-D

I added a few more photos today showing the fiberglass rods used to cover the fragile brass rods.

On your reception issue I had a similar instance where my "tuned" aviation antenna performed worse than a random whip, until I used this filter:

If you live in a metropolitan area your scanner may be loosing it's sensitivity in the airband due to strong TV/FM broadcast stations? It was like night and day using this filter. It really made a difference.

Have fun on your antenna projects :-D

Ken (N6GOH)
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Chadan on August 15, 2011, 06:58:31 PM
Hi Ken! It's a great looking antenna and easy to build, but the 5' whip on my monstrous scanner is working pretty well. I live in rural Iowa so I don't suspect there is too much interference. I spent a lot more cash on this antenna than I planned to and was pretty discouraged with the results. Thanks for the link but I don't see myself spending much more on filters and the like until I am really convinced that it would be significantly better than the whip.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Tomskii on January 05, 2012, 10:12:02 AM
How far (mileage) do you reach with this antenna. My (non DIY) antenna goes aroudn 30km far but getting atc is still a now and then. (cellphone pic)

Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Chadan on January 05, 2012, 10:25:25 AM
Hi Tomskii. It's hard to say how many miles out I can hear. How do you measure that which you cannot see?  :-D

But I don't think I pick up anything further out than 10-15 miles. Their are several airports within 20-30 miles or so, but the chatter I hear is usually planes calling in their proximity to said airports when the planes are pretty much directly over my house  :|

And I usually cannot hear the local airport transmitting even though I am about a half mile from the FBO! I haven't messed with it in a while though.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Tomskii on January 05, 2012, 10:28:28 AM
Cheers for the reply, seems like my antenna performs better then, as I do get atc normally but depending on where I am of course it is less. I should be starting a feed soon on here as well if all goes well. :)
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Chadan on January 05, 2012, 12:05:44 PM
good luck to ya!
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Chadan on March 05, 2012, 04:43:38 PM
My reception has been boosted using a home-built Yagi antenna as described in this thread:
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: RonR on March 05, 2012, 07:12:04 PM
Hi everyone,

I going to take a stab at building my own 3-element Yagi.  Just had a couple of questions that hopefully someone might be able to answer: in that PDF article the author states that he prefers wood over PVC pipe for the there a performance difference between the two?  I don't think there would be but I could be wrong.  And the other thing was regarding the elements: I scrounged around in my basement and found 1/2 inch copper pipe and some smaller diameter aluminum tubing (probably from an old antenna).  I was thinking of using the copper pipe for the driven element and the aluminum tubing for the other two elements.  I have just enough of the copper and aluminum for one antenna.   Does anyone see any issues with this plan?  If this antenna works as well as others have said, I would consider building two or three more and point them in different directions.  My wife will love me for that :) Any insight would be appreciated!  Thanks, Ron.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Chadan on March 05, 2012, 07:48:39 PM
Hi Ron. From the PDF referenced in the other thread:
The elements can be between 1/8 and 1/2 inch in diameter without changing performance. For the driven element you really want to use a material you can solder to.
Other than those paramaters, I don't think diameter or material is very important. And yes, wood and plastic work just as well for the support beam since they're basically inert to radio signals.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: RonR on March 06, 2012, 11:29:06 AM
Yes, that's what I thought.  Thanks for confirming.  There are a few ZBW frequencies where the ground signal is floating just around the noise level.  I'm hoping this antenna will improve that.  I'll let you know...
Regards, Ron
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: InterpreDemon on October 13, 2012, 03:13:45 PM
Ron, the main difference between wood and PVC for the boom is that the PVC will eventually droop and the wood, if you use a good grade hard wood and seal it, will not. Personally, I prefer neither and always use metal, applying a boom correction factor to the element lengths which, for your purposes, would be about half the diameter of the boom. There are some good, free design programs on the web, and for a three element one in particular, by VE3SQB, has an excellent algorithm for an enhanced three element yagi:

He has many other useful programs and links as well.

To test the model produced by his program you can use an on-line applet to re-create the dimensions and plot the gain pattern, SWR and such:

You can also download the demo version of EZnec to do the same, but that program, though it allows far more accurate modeling right down to elevation, ground quality, mast/tower effects and transmission lines, is also more difficult to use since you have to literally specify the 3D coordinates of the end points of every element rather than simply entering the length and distance of elements for a particular type of antenna:

Alternatively, if you want to have a gain of 8db or better and match below 1.5 from 119 through 131with enhanced performance between 129 and 130 for company channels you can just build a 4 element beam I designed and built for the purpose using 3/4 inch elements and a 1.25" OD boom, all aluminum. It has a good match for 50 ohm cable, so you can feed it directly even though I always use a 1/1 coax BALUN. It is an excellent performer for any off-field feed of an airport served by major airlines with ground traffic and such from a distance of up to fifteen or twenty miles depending of course upon the path and elevation. Element dimensions and performance plots attached.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Chadan on October 13, 2012, 03:20:32 PM
...Element dimensions and performance plots attached.
Phenomenal information ID! Maybe I can't see the design specs in the four attachments.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: InterpreDemon on October 13, 2012, 04:41:19 PM
The very first one, "elements.txt" gives length and distance from the rear (reflector) element, which is datum zero. Distances are center to center. The fractional values in parentheses represent the decimal values in case you need them. I also have the corrected lengths for the 1.25 aluminum boom, so if wood use the middle and aluminum use the far right. Also, keep in mind these elements are 3/4" OD aluminum, which is what enables the high bandwidth and I suggest you stick with same because the design is fairly critical and required a great deal of experienced tinkering to obtain the desired performance envelope. I use 3/4" aluminum tube bought at the hardware store, and for the split driven element center support I take a 6" length of 3/4" hardwood dowel and turn it in the lath to the ID of the tube, leaving the center 1.5" at 3/4" where it passes through the boom, then sealing it with lacquer or varnish. Don't forget to put a cap, wooden or epoxy plug on/in the top driven element so it does not fill up with water. A single SS sheet metal screw 1/4" from the driven end of the elements both attaches the feed lines and secures the element. Make sure you go to the marine store and buy marine grade, heat shrink ring terminals and SS star lock washers for those connections, followed by a liberal dose of spray lacquer over everything after final assembly.

Speaking of feeds, as I said you can probably do fine attaching RG-58 directly to the elements, but if pattern consistency is important across the band you really should feed it balance by use of a BALUN, which for this antenna can be nothing more than a "Y" made from a quarter wave (15.6") and a three-quarter wave (46.8") section(s) of RG-58 with the two center conductors driving the elements and the shields grounded together at the boom/dowel cross bolt. The whole thing can be enclosed within the boom if you want since there is plenty of room to pass RG-58 past the reflector element inside, just pop the two ends out a hole just short of the driven element, attach and seal everything up. The way I do it is a bit exotic due to a marine environment and preserving the option of having alternate BALUN tuning or repairing lightning damage without removing the entire antenna. That assembly is a 3/4" copper tube with an "N" male bulkhead connector on the input side where the hardline connects, an internal "N" male connector forming the center of the "Y" and the opposite end capped with with two through-holes for the two coax lines, shield folded back and soldered to the outside of the cap and the center conductors and the entire top of the cap encased in epoxy.

One other important thing about feeds... the dimensions for the driven element are the total length, which includes the length of the feed pigtails from the point they leave the coax shield, so it is very important that you make these leads identical and as short as possible, going directly to the element, and final-trim the elements to specification. There is no boom correction factor for the driven element because it does not pass through the boom.

Regarding the boom, it is 1.25" OD aluminum thin wall tubing. After drilling pilot holes at the proper locations and enlarging them to 3/8" I use a two-piece Greenlee punch to punch them out from the inside out... shoving the punch down the inside of the boom with a rod, lining it up with a philips screwdriver and threading the punch draw bolt in from the outside. A single SS 10-24 screw through the boom and element holds things in place, you square it up and then use a center-punch to ding around the boom holes to tighten up the fit, or you could put a fillet around the joints with some PC-7 epoxy or get a buddy to drop a couple spot TIG welds.

It's a very nice antenna, and if you build it... the signals will come.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: Chadan on October 13, 2012, 04:53:31 PM
Not sure how I missed the first attachment. Thanks for explaining! Sounds like a really nice antenna. How much are you charging to make them?  :-D

This is good stuff and very detailed, but it'd be nice to have a simpler instruction set. I think most folks want to make just a couple trips to the hardware store and make a day out of it. The level of specifics are a little intimidating to me.
Title: Re: KAMW feed setup and home-built SO-239 antenna
Post by: InterpreDemon on October 13, 2012, 05:22:34 PM
Well, I've been doing this for a long time and approach it from commercial experience, but if you do it with a wooden or fiberglass boom it really can be an afternoon project as simple as using  and eight foot length of 1x3 (edge "up") for the boom, attaching the elements across it with a couple screws on one side and stapling your feed line to the opposite side of the boom. Toughest challenge there is a good way to attach the boom to your mast or tower since it is heavier and the torque greater, both in holding it up and dealing with the wind, but you can certainly run a brace up to the back of the reflector element from below, and the further the reflector is from the mast the better. IF you're really lucky you have a tree or a properly oriented second floor corner of the house you can screw it to.

If you do use wood AND don't want to bother with a BALUN I would recommend wrapping a coil of about ten to fifteen turns of your coax around a 3/4" dowel right before the feed.

I could build you a kit I suppose, but it would probably be too expensive in light of all the cheap "ham consumer" alternatives out there. Maybe if there was a need for a dozen or so it might be worth considering since scaling would definitely bring the costs and time down significantly. I put that design out there for the benefit of our little community and wasn't really thinking about it as a commercial opportunity... but if anybody else does that's fine with me, I'll sue them if they are successful :-)