Dipole Antenna

This is a dipole antenna some one came up with for a ultralight .

Looks like a very good article and neat project. Might be kind of tough to find a mounting spot on a gyro. The article is available as .pdf from this link:

PDF Copy of Article

I have a book known as the antenna bible if anyone needs it. Packed away somewhere. Joe Carr is author ?? something like that.

I'm pretty sure Rocky Me Lad has one like this on his Desrt Bee.

A couple of more thoughts about dipoles.

The radio waves radiate perpendicular to the transmitting element (the one attached to the center of your coax). Ideally you want this element oriented as vertically as possible so you are radiating in a pattern (think of it as a donut around your antenna element) 360 degrees before, behind and to the sides. If the antenna is oriented horizontally, you are radiating mostly up, down and to the sides.

The orientation of the counter-poise relative to the transmitting element also adds a directional component to your signal. Basically, the signal is strongest in the direction of the mass of the metal counter-poise. So if you install a V-shaped dipole as pictured, your signal will be strongest at the center of the V.

RF antenna design is more an art than a science. Lots of books and lots of competing theories. In the real world, especially in the DoD, design is empirical and then justified by developing a theory to fit them!

Someone mentioned an expensive cap helped their system. Was this used to clean up the power supply to the radio?

gyromike said:

I'm pretty sure Rocky Me Lad has one like this on his Desrt Bee.

Click to expand...

Very close. Mine is bent away from the coax and turned 90 degrees (ie. vertical). Works great, but piano wire will collect iron oxide with time, so periodically clean and coat with a light oil. And did I mention CHEAP.

Very nice, RockyMeLad.
Several things to point out in this simple installation.
An insulator. Even a section of gallon milk carton works well.
Probably 1/4 wave (24") transmitting element and counterpoise.
And a very tidy loop on the end to serve as an eyeball protector.
Be sure to inspect your coax-to-element junctions occasionally to be sure they are mechanically and electrically secure.

Yo Penguin,

It's an old scrap of 1/8" nylon sheet found lying about at the hangar, but you're right... any insulator would work. Cheap plastic cutting boards are also readily available.
The "periodic check" is usually the annual on the bird, and I use an electrical anti-oxident at the connection. Seems to work well.

I bought one of those Mobile One antenna with the ground independant. Unscrew the ground independant part and throw that bit away. Make up a piece of stainless rod the same length as the top aerial and attatch it where the ground independant part was. It works great.
Colin

Colin I was about to purchase one of these MobileOne AIRKIT Aerials $125 plus GST and $15 delivery.

They come highly recommended by some Oz gyro gurus.

If you throw away the bottom section and then added a piece of stainless, wouldn't it be cheaper to make the PDF file dipole 1/2 wave aerial in the first instance?

I mean I dont know I am looking for advice and had thought this home made job might improve my lot....then I got told about the Mobile One AIRKIT and how damn good it is.

It looks a lot classier but is it worth the extra bucks straight up especially if the home made system produces the goods.

Still deliberating

Mitch.

G'Day Scott,

Thanks mate for posting this thread. I have been plagued with radio and headset probs for to long now.

Cheers Todd for posting the PDF file link.

RockyMeLad, pictures tell the story and yours apparently is a successfull one.

Went to town today for an MRI and did some shopping. Launceston, Tasmania is not a big place really and I have always struggled to get even basic stuff for the gyro. Didn't have high expectations.

Hit the local UHF CB Radio Tech Shop and came home with:-

2.5 meters of PEI RG58 C/U Mil-C-17F
1 BNC Panel Mount Connector (Bloke said he wouldn't have one,came back with the unit, said we don't normally stock these)
2 BNC Coax End Fittings
1 BNC Aerial Adaptor (Screw type)

Bloke in the shop fitted up 6 feet for me. Rigged/crimped the whole RG58 coax, connected it to my radio via the BNC aerial adaptor. Had him give me a couple extra feet for working up the Balun.

Cost $33.50 that included the GST (all taxes)

He was 'keen as mustard' to hear how the project comes along. Told him I would mount it up front initially and see how I fare.

Joy of Joys, he has a SWR unit and will let me park the gyro up and do the job on it to find the optimum spot. This will work, as he is in a large industrial area, so the noise of the gyro wont bring to much attention, whilst testing.

I will advise when I have the aerial ready for testing.

Thanks to all.

Mitch.

Sounds like you are sorted.
I bought the mobile one aerial because a friend recomended it but found it lacking. On investigation I was informed the Ground Independant part let it down. As I had already purchased it, the option I came up with was to throw that part away and improve it my own way. Looks tidy and works very well.
Colin

Colin - as I recall, the 'ground independent' part of the MobilOne aerial consist of a coil of wire wound around a spool. If you took a 1/4 wave (or more) of copper wire and wound it around a wood dowel it would electrically satisfy the requirement for a ground. But in practice, it would be sorely lacking. The more metal in a straight shot you have, the more effective the ground plane will be.

Correct Larry.
That's pretty much what I did. Tricky part was making up the fitting to attatch it as they had cut an unusual thread on the mount.
Colin

Works a Treat

Works a Treat

Made the dipole aerial up and set/tuned it for midrange of my local stations.

All test so far ground static tests with new dipole aerial attached to the Vertex radio.

George Town 127.3 (Main station)
Cranbourne 126.7
Devonport 126.9

Tuned at 127 MHz

Launceston ATC 118.7 I read loud and clear all traffic.


I am picking up what I believe is Melbourne ATC on 125.5, not sure which airport. It to sounds like its comming from the bloke next door.

I wasn't getting so many channels nor such good reception previously.

I made a brief call to Att traffic GeorgeTown and got a good well read response from their base station. Ground to ground opps over 6 or 7 miles as the crow flys.

The testing we did clearly indicates the omi-directional qualities of this aerial.

Looking forward to testing on the gyro, mounted as per pic posted above or similar. Hopefully this coming Monday.

I sprayed the elements and board etc. I also added some tiny plastic ties to lock the elements in place.

Mitch

Hello Mitch,
So how did the antenna work on the gyro and in the air ?

Scott

G'Day Scott,

Had a nice flight yesterday before I mounted the aerial, as a storm front was approaching.

Then I mounted the aerial.

I'm getting incomming from 400 kms away ATC Melbourne, 65 kms ATC Launceston and ground test have proved comms is excellent over good distances. For example I called GeorgeTown 5 miles from as a ground test. Base station read me loud and clear and vice versa.

Have mounted it up front as a proof of concept and will likely end up mounting it, partially imbedded perhaps, in the front section of the instrument pod.

I have not had this capability with the little ducky aerial.

Will advise after further testing.

I'll be interstate for 10 days so I'll get back to you after aerial testing.

Cheers Scott,

Mitch.

Mitch,

Has someone pointed out that your gyro has grown some whiskers?

Looks like a World War 2 night fighter.

Jordan

Hey Mitch,
This is how I mounted my antenna . I'm not sure if it takes away from its performance . I have no meter to test it . But to me it work really good. With the pod you don't have as many options .

Scott

Well I'll be dipped....I thought that type of antenna would only work well if it were mounted vertically; the horizontal reception "dead holes" would seem to be to the left and right sides instead of up and down....