Stupid antenna question

[w3bny]

Ok you wheezles... Todays stupid antenna question.

Background data: Stupid bunnies at Lapin labs (of which, I am chief experimentalist :spin: ) are getting ready to launch a balloon lift antenna but one thing confuses me. To use radials or not.

My thought, its a vertical antenna and the performance is going to be poop if I dont use them. Research online that I have been doing shows them and kite lifted antennae as NOT using them at all. Yeah, I know the answer would be to pump it into EZNEC and see what the numbers say but alas...ahm too broke to pay for it!

So any of you guys that have used balloon/kite lifted antenna, your radial thoughts are welcome.

[NQ6U]

Make it a 1/2 wavelength antenna and you won't need radials, maybe just a short counterpoise. Shorter than 1/2 WL, though, and you'll need some sort of radial system.

[ab1ga]

I remember two articles about balloon lofted antennas in QST over the years.

The first was a club at Ohio State University; they used kitoons (blimps with fins) they got through military surplus to loft a 160m vertical antenna.
They did in fact use a "counterpoise" - "Big Ear" - the radio telescope at OSU, which was basically a sheet of copper the size of a footbal field.

The second article was in QST within the last five or six years. That Field Day group didn't use a vertical, but a loop antenna, I believe diamond shaped, fed at the bottom. This antenna obviously needed no ground plane, but the guying was more complicated because it had to retain at least a little bit of shape. I'm sure you'll be able to find an aging sailor who knows his way around rigging to take care of this for you. :-)

You could also look at variants of the end-fed Zepp antenna. Originally designed for use aboard, you guessed it, Zeppelins, it requires no set of radials, but since you want to feed it from the ground, you'll have to deploy it "upside down".

Regarding antenna modeling software, you may want to look at 4NEC2, which the last time I checked was free. Written by a Dutchman, so what could go wrong?

73,

[WØTKX]

Most use a vertical, but a circular polarized antenna would help. We have a very active balloon group here.

Rob the prez is a buddy of mine. http://www.eoss.org/

[kd8dey]

Curiosity, Hf Vhf Uhf??

[W5RB]

Do use a bleeder resistor at the base . The potential for static buildup is great .

[KG4CGC]

Do you have a groundable antenna tuner for a longwire?

[w3bny]

Curiosity, Hf Vhf Uhf??

HF of course. I could be stupid and try 6m but it would be the wrong polarity and if I am not mistaken would be looking at what...+/- 70db of loss right off the git-go?


Do use a bleeder resistor at the base . The potential for static buildup is great .

Good Gawd yes! I acquired another ICE Supressor (http://www.iceradioproducts.com/impulse1.htm) just for that purpose. Mr. Coulomb has a big potential for lulz with balloon and kite antennas...many thousands of lulz.... Seriously, I will be using snap hook on the wire as the balloon/kite pays tied directly to ground out then when I hook up to the radio it will go thru the ICE for the surge/bleed.



Do you have a groundable antenna tuner for a longwire?

Yeah, planning on using a remote MFJ auto-tuner that I acquired as payment for services rendered..(OY-OY!! clean thought you bastridges!)

I have enough, well, more than enough copperweld to take care of a full wave antenna on 160 (or more) but will keep it at or under a half just for the counterpoise/radial issues and to keep myself out of trouble with the FAA!

[ab1ga]

Mr. Coulomb has a big potential for lulz with balloon and kite antennas...many thousands of lulz....

You ain't kidding. Ben Franklin was chugging along like gangbusters until he did that experiment with the kite, and then he came up with the idea for Daylight Savings Time!

[w3bny]

Doing some more google crunching... It looks like I am going to shoot with a 5/8th wave. Best low angle, shouldnt need radials or a counterpoise like the 1/2 wave should (even though its like .05wl). But, will definitely have make a loading coil to help cancel some of the reactive component. And a nice air wound coil I gots.

More later!

[W5GA]

You need this to ensure success

[w3bny]

HAH!! Never saw the add before..funny

[WØTKX]

Yea, my EOSS buddies are into VHF/UHF.

Don't forget that a dipole can be vertical, and an OCF dipole with the shorter leg down might be practical. Tried it with a box kite a few years ago with some friends, and it worked well. Fed with ladder line attached to the kite string so as to not put strain on the feedline... and the 30% lower part of the OCF dipole had a separate line so you could pull the antenna more vertical, with the feedline arcing away at about a 70 degree angle.

Was setup to play QRP on 40 meters, and it kicked ass.

[w3bny]

Yeah I thought of that too... Multiple balloons/kites for larger configurations....but little hops for us here at Lapin Labs.

[W1GUH]

You'll want something for a counterpoise to work against the antenna. A ground, or one 1/4 lambda radial should do.

[WØTKX]

Unless it's a dipole.

[W3WN]

Ren, it's actually quite simple.

If you're loading the antenna as a 1/4 wavelength vertical, or variation thereof (3/4, 5/4, etc. depending on the band) then you need radials or an equivalent counterpoise. If you're loading it as an end fed 1/2 wave, or an Off Center Fed (OCF) dipole, then you don't.

You can, with a decent tuner, load a 1/4 wave without radials, but I don't recomend it. Getting a good SWR match is one thing, but radiated signal (if any) is something else. A 1:1 SWR on a poor antenna installation may mean that you're warming the wire, but not radiating.

Also, the radials (counterpoise) do have an effect on the radiation pattern. NVIS verticals have advantages for local communication, but if you want your signals to travel beyond the horizon, you need the radials.

Remember that essentially, the 1/4 wave vertical represents the "hot" half of a dipole. The radials represent the other half. No radials, then you're relying on the reactance or conductance of the actual earth beneath the antenna. If the earth under the antenna is a poor conductor, the antenna won't work well.

I speak from long and hard learned experience on this one!

73

[NQ6U]

A 1:1 SWR on a poor antenna installation may mean that you're warming the wire, but not radiating.


In other words, you're transmitting into a dummy load. Even notice how you get a perfect 1:1 SWR on a dummy load?

Think of the 1/4 wave vertical section as half of a dipole. The radials work much like a mirror and take over the function of the missing half.

[W3WN]

In other words, you're transmitting into a dummy load. Even notice how you get a perfect 1:1 SWR on a dummy load?

Think of the 1/4 wave vertical section as half of a dipole. The radials work much like a mirror and take over the function of the missing half.Exactly!

I never really understood how this works until I took a Physics class in college. Sadly, I lost the textbook in the aftermath of a heavy post-hurricane rainstorm a few years back, so I can't quote from it. Regardless, seeing the physics behind the theory was most illuminating. And the calculus backs up the common theory... a few radials are better than none, and after about 30 -40 radials (evenly scattered around the vertical section) are usually more tha sufficient... beyond that, you're achieving minimal gain for a lot of effort. After about 60, the gain is virtually negligible.

That, and the lovely calculus of the impedance vs. wavelength. Good old f(x) as x->0. As you get closer to a half-wavelength, you approach infinite impedance. But the impedance doesn't go sky-high until you get close, and that's why a 5/8 wave antenna will work... it's close, but not close enough.

[W1GUH]

'WN said:


You can, with a decent tuner, load a 1/4 wave without radials, but I don't recomend it. Getting a good SWR match is one thing, but radiated signal (if any) is something else. A 1:1 SWR on a poor antenna installation may mean that you're warming the wire, but not radiating.

Had a great practical demonstration of that here. Back when I could actually hear signals here, I was working on getting a random wire out the window going -- I used #26 magnet wire hung out the window. It tuned OK without a ground. But then when I hooked up a ground, things got exciting. Seems the wire was laying on some metal. Without a ground, there was so little power in the antenna that it didn't arc. Soon's I hooked up the ground (radiator) I realized that I had to get the wire away from the building.

But never did -- by that time the hi-rise next door had wiped out any chance of ever hearing anyone...sigh.

[NQ6U]

a few radials are better than none, and after about 30 -40 radials (evenly scattered around the vertical section) are usually more tha sufficient... beyond that, you're achieving minimal gain for a lot of effort. After about 60, the gain is virtually negligible.

You're right. There was an article in QST about that last year some time; the authors erected a quarter-wave vertical and played with various numbers and positions of radials. 32 flat on the ground was indeed the sweet spot but they found that 16 was probably adequate in most cases. Interestingly, they found that if you elevate the radials to about five feet (1.5m) off the ground, you could get by with a lot fewer of them. I can't remember the exact numbers but it was a significant difference.

[W1GUH]

"...but they found that 16 was probably adequate in most cases. "

Sounds about right. But in those situations where that number is not possible, fewer will work OK. If ya can't to what's optimum....do what you can do to get on the air. I once had a Hustler 4BTV & the only possible number for me to use was 1. Count it. 1. Worked OK...had lots of good contacts.

Another time on a field-day setup I had the vertical mounted on a dock in a lake. Again, 1 radial, but made lots of contacts. I'm going to have to go through my QST's. I may have that issue and would really like to read it. Did it quantify the differences between different numbers of radials?

[NQ6U]

Did it quantify the differences between different numbers of radials?

Yes, they had it all laid out nicely with tables and charts. I just checked the ARRL Web site (their search function really, really sucks, BTW) and the article is in the March 2010 issue: An Experimental Look at Ground Systems for HF Verticals, by Rudy Severns.

[W1GUH]

Thanks...I probably have it around here somewhere.

Yes...the ARRL site does leave a lot to be desired.