Small Lot antenna idea...

[Ed/KB1HYS]

The Station is off the air since we are rebuilding the laundry room where it used to be... 

So I was modeling some ANT ideas.  Here's one for a 20 meter yagi on a small lot.

Basically you lay the dipole on the end of the roof with the feed point at the peak and the wires running down the slope. (This could be very stealthy too if you need to avoid Covnenants).  Allow the ends to dangle or run them back up under the eaves.  Lay a second wire ~8ft back from the dipole parallel and about 5% longer this is a reflector.  ( you could add more

I modeled it based on my single story ranch with a shallow pitched roof. If I layed out 2 reflectors it showed ~7dBi gain.  Even if it's half that in reality, there should be some gain. 

You could lay the dipole in the middle of the roof, and add directors, reflectors and a few relays and you could switch direction 180.

Ok so ITS NOT rotatable, if your house happens to be pointed east-west or close you should still be able to get some gain in an interesting direction.

If you had a taller house that would surely help, I think you could also go lower in frequency as well.

A wire diagram from EZNEC and the Far Field Elevation plot.  Looks promising, what'cha Think?

[Pete, WA2CWA]

Is metal roof flashing used on your roof or aluminum/metal gutters? Is there insulation with aluminum backing used in the attic or area nearest the roof? All could have an effect on antenna performance. Put up a dipole and try it. What do you do when it's completely covered with snow?

[Ed/KB1HYS]

Good questions Pete,

I do have flashing on the edges of the roof, but I figured that since it crossed at right angles it wouldn't be to strongly coupled to it. (just a guess).

I hadn't thought of snow...    though since my roof is poosrly insulated, the snow doesn't last long anywya.

[WBear2GCR]

People I know who have put ANTs inside of the attic have never done well. Something like 20dB less than the identical ant outside and strung between two trees.

I say put up a flagpole.

No one will ever complain about a flagpole. Eh?

Your flagpole needs to have two pulley systems, of course.

This give you the options:

- shunt fed vertical
- J pole
- inverted L
- inverted V center support
- and a few others not as simple...

I think a 60+ft vertical, oops... I mean flagpole is VERY PATRIOTIC!!
Just be sure to fly a flag?

If you buy a fiberglass pole you maybe can get it with helical windings embedded??   

           _-_-bear

[Ed/KB1HYS]

Actually this was intended to be outside the attic, just laying on the roof.  Talk about an easy installation, and adding elements is just as easy.

A compromize antenna certainly, but with interesting possiblities.

[WU2D]

Dr. Evil's Ham Lair

First several ground radials are installed inside the attic space. Elevated drooping radials - very effective for a ground plane.

Cut a hole in the roof and install a remote controlled door. After dark, the door opens and a black helium balloon automatically reels out a quarter wave of wire. After ham activities the device retracts into the attic. 

MUUUUHHUUUUHHAAAHHAA

WU2D Mike

[flintstone mop]

The antenna performance is dramatic when inside an attic and outside. Electrical wiring, the nails used for the lumber and shingles, etc etc. 10M might not mind being inside, but nothing lower in freq.
And you shouldn't lay the antenna elements on the roof either. Two 25 masts supporting the antenna would be ok.
How long is your roof? Are you trying for 80M?

Fred

[Pete, WA2CWA]

And, if you have any florescent or neon lamps anywhere in your house, they will probably dance to your transmissions. Then, there might be the issue of RF coupling to other metallic things anywhere in the house. You'll have to put up signs on stuff that say "Don't touch this when I'm transmitting". Finding a willing tester might be difficult.

[Steve - WB3HUZ]

Looks interesting. You'll never know until you try. I think the major factor will be how much coupling occurs between the antenna elements and the roof. The dielectric of any of the roofing materials is obviously different than air, so some pattern change/distortion could occur. Will it just be straight absorption/attenuation, thus less gain or actual pattern skewing? Dunno. You may end up changing the length and spacing of the element to compensate. Some of these potential problems could be reduced by spacing the element even 6 inches above the roof.

If you try it, let us know how it works. G6XN writes about a similar setup in his book. I'll have to pull it out and see what he says.

[Ed/KB1HYS]

Well, I guess I could space it up off the roof with some fiberglass rod (driveway markers come to mind) that might help if it gets to live until winter.

Wonder what the XYL will say about THIS project???

[WBear2GCR]

I would definitely not lay the elements on top of anything.
It is a minimum a fire hazard.

It will not work properly since the roof looks something like a ground... it is a leaky insulator at best and when wet will get quite leaky in more ways than one.

Otoh, you could put up three or more center supports in the form of short "spikes", I'm talking 3-4 feet high. Sort of a lightning rod effect. Keep them thin, like a stainless steel whip antenna - you can buy the same alloy in 1/4" diameter or 3/16" diameter from a metals supplier, even shippable via UPS. They will be practically invisible to the eye from the street.

Now you hang ur wire off that. Ground the rods with serious ground wire, and you've also protected your house from lightning hits at the same time.

Use a short kevlar or nylon line with a transparent plastic or similar insulator at the ends and the ant will be more or less in the air.

Since you can use a matching method that works on grounded elements, you can ground the whole thing anyhow...

Now that would work.

Rotating the house, that's another matter...

         

                  _-_-WBear2GCR

[KB2WIG]

 " Wonder what the XYL will say about THIS project??? "


Throw up some Christmass lights.... ..


klc

[AMroo]

What if the XYL doesn't like it?



I know one guy who bought a small classic bit of 30's gear and really loves it, but his XYL wont let him bring it in the house.
Or any piece of equipment or even component in the house, Jeeezzz.........

What if the XYL doesn't like it?
I used to have one like that, new one says "as long as it makes you happy".

[WA1GFZ]

If XYL doesn't like your radio I hope she has something better for you...

[KX5JT]

What if the XYL doesn't like it?



I know one guy who bought a small classic bit of 30's gear and really loves it, but his XYL wont let him bring it in the house.
Or any piece of equipment or even component in the house, Jeeezzz.........

What if the XYL doesn't like it?
I used to have one like that, new one says "as long as it makes you happy".

"I used to have one like that,........"

Ya done good!

[N3DRB The Derb]

my wife drives me 900 miles to pick up transmitters. 

She's the bestest wifey EVAR. 

[WU2D]

Yeah when I got cancer at 45 and almost SK'd things loosened up a lot! Both of us say NO less often now. I can honestly say that nothing kills a midlife crisis faster than C.

I had the easy part - all I had to do was survive. I do not relish what was going through her mind 5 years ago with two kids and a husband at mid career about to go away.

Mike WU2D