An Idea from my wife.

flyingwolf · #1 (**permalink**) 08-08-2005, 05:54 PM

As I was annoying her with antenna properties and what a 1/4 wave 1/2 wave was and how it worked. She came up with a pretty good idea.
Rather then using single pieces is wire for each element how about using a few old radio telescopic antennas.

I thought about it for a second and thought to myself its a great idea.
We know that the metal is very receptive. We know that they work great as antennas. And it would be perfect to use 3 of them mounted to a small copper rod and able to be resized quickly and easily for different bands.

So any reason why this isn't a good idea and why I should go to the storage bin and start looking for all my old radios and harvesting the antennas?

Thanks for any and all advice.

kb2vxa · #2 (**permalink**) 08-08-2005, 07:17 PM

High Flying and readers,

It all depends on the length of the telescopic rods and how many bands you're scanning at once. Scratching my noodle I come up with "How FEW elements can I get away with?" if you know what I mean. Then again it depends on whether you're building a groundplane or fan dipole, the groundplane requires half the elements and a set of fixed length radials 1/4 wave at the lowest operating frequency. In either case fan the elements to minimize interaction. What you plan on using for an insulator and other mechanical considerations I'll leave up to you and the ideas you get from exising antenna designs. Hint, pictures don't tell the whole story, look at a few commercially built ones up close and personal.

Oh, tell your wife she's a smart cookie, I like that in a woman.

xusmarine1979 · #3 (**permalink**) 08-08-2005, 07:21 PM

Does anyone have a link he that could help him out with?

flyingwolf · #4 (**permalink**) 08-08-2005, 09:43 PM

Her main idea was that since they are teloscopic antennas then you would be able to easily set them to the correct size. I am sure her main reasoning is so I am not making a mess in the house.
Bassicly I could take 3 antenna elements. Fabricate a small mounting base for them all fed into a single board-mount PL-259 connector. I would still of course be using copper rod for the ground plane elements. But the other elements would be esy to adjust for different frequencies quickly without having to make any major changes to the antena other then a simple lenght adjustment on the telescoping element for the band you want.

This would of course be for receive only.

Dang her. She got me thinking now lol.

And yes I am very lucky. When we are working well together we can come up with very good ideas.

Al42 · #5 (**permalink**) 08-08-2005, 10:45 PM

Quote:

Originally Posted by flyingwolf

So any reason why this isn't a good idea

The resistance between the telescoping pieces (the only thing connecting them is the phosphor-bronze springs) makes a telescoping antenna less than ideal.

That's no reason to not make a little telescoping ground plane and see how well it works.

flyingwolf · #6 (**permalink**) 08-09-2005, 09:06 AM

I may just toss one together for grins and giggles and see how well it works. I have no testing equipment to say if it made any improvement, but I wil llet you know what my ears think.

Of course anything wil lbe better then my rubber duckies.

MarkEagleUSA · #7 (**permalink**) 08-09-2005, 09:53 AM

This idea sounds interesting...

Quote:

Originally Posted by kb2vxa

the groundplane requires half the elements

What is meant by "half the elements"?

Quote:

a set of fixed length radials 1/4 wave at the lowest operating frequency

Is there a magic number of how many radials to use, or would it be 1 radial per vertical?

Quote:

fan the elements to minimize interaction

Does this mean the verticals should be on a small angle away from the centerline? i.e. this || vs this \ /.

kf4lne · #8 (**permalink**) 08-09-2005, 04:26 PM

Use at least 2 radials, but 4 would be better. I have used brass plate like what they have at hobbie shops to mount several elements to a SO239. If you harvest antennas get the whole antenna, mounting base and all. get a peice of copper or brass plate large enough to solder your elements to and solder the elements to it and leave a hole in the middle to attach the SO239. Use ground radials for the lowest frequency you have an element for. SOlder the radials to the mounting holes in the SO239 and solder the plate with the antennas on it to the center pin of the SO239. set the 2 short elements out at an angle from the long element so they wont interfere with each other and you should be all set.

MarkEagleUSA · #9 (**permalink**) 08-09-2005, 04:32 PM

Regarding the elements, does it matter what wavelength they're sized to? Do they all need to be the for same wavelength?

kf4lne · #10 (**permalink**) 08-09-2005, 06:04 PM

each element should be sized to the frequency range you want to hear. Example - VHF-LOW about 60 inches, VHF-HI about 20 inches and you can use teh UHF element for 800/800MHz too at about 7 inches

MarkEagleUSA · #11 (**permalink**) 08-12-2005, 06:56 AM

Quote:

Originally Posted by kf4lne

Example - VHF-LOW about 60 inches, VHF-HI about 20 inches and you can use teh UHF element for 800/800MHz too at about 7 inches

If my lowest target frequency is 35 mHz, and the radials must be 1/4-wave of that, then they would need to be 84", correct? If so, that makes for a pretty unwieldy setup.

Giving up VHF-Lo and going with VHF-Hi, the radials would only need to be about 19"... much more manageable.

Now I see why multi-band antennas are one big compromise!