Inverted "V" Attic Antenna Using Mobile Whips

[Riverman]

My previous setup: A homemade horizontal dipole using two 4' Firestiks atop a 15' mast.

I am now using a similar antenna in an Inverted V orientation in my attic.

The advantages:

1. The attic allowed me to gain a few feet in height over my 15' mast.
2. The Inverted V is more omni-directional than the horizontal dipole I was using.
3. With the coax hanging straight down from the feedpoint, the impedance should be closer to 50 ohms than with the horizontal.
4. In the attic it's protected from weather.
5. It's STEALTHY!

Here's the build:

I began with a Simpson Strong Tie #LSTA12 from Home Depot. This version is very thin and lightweight.

And it bends easily!

For increased rigidity I added a small "L" bracket.

This strong tie comes with a couple of 1/2" diameter holes which I used for the stud mounts. Using nylon washers, I isolated both antennas from the bracket. I then snugged a small zip tie around the coax and through an existing hose for strain relief.

To suspend the antenna from the rafters, I used a piece of coat hanger and two other existing holes.

The finished product!

In place!

All that's left is to connect my 23 channel Cobra 85 Dynascan and check the SWR.

CH 12: A tad over 1.1

Channels 1 and 23 were both 1.2

The Firestiks I used have adjustable tips on top but no tuning was necessary!

The skip was rolling in from everywhere: Boston, Mobile, Honolulu and Barbados! After several minutes of trying without success, I finally connected with a fellow in Rhode Island. Not bad for a homemade antenna, a 40-year-old radio with a stock mic and 3.5 watts!

Is this a great hobby or what?

My thanks to John Reisenauer and Scott Wolfington whose articles started me down the path of using mobile antennas for my base station.

http://www.hamuniverse.com/cbstrongtie.html

 

[M0GVZ]

I don't understand why you didn't just make it from wire.

 

[w9cll]

Nice project but wire is simpler and easier.

 

[Riverman]

Guys, a wire dipole takes up a whole lot more room. This is much easier to hang and move around if needed. (Didn't need to.) And this antenna can be situated farther from my AC/Heating Unit than 17' of wire. Plus, it was just fun to make!

 

[M0GVZ]

Looking at that photo you've got a ton of room to fit in a wire dipole. The legs can be bent as required to fit.

 

[Riverman]

Looking at that photo you've got a ton of room to fit in a wire dipole. The legs can be bent as required to fit.

MOGVZ,
I'll probably try one someday to see how they compare. Will report back if I do.

 

[Riverman]

Okay, I put up a half wave wire dipole for comparison purposes. Made it out of a 10' electrical extension cord. An Inverted V Dipole calculator said each leg should be about 98 inches. That worked perfect. SWR is less than 1:1 on all channels without any adjustments.

Couldn't get all of it in the picture. Kinda hard to see the gray coax hanging straight down. I have egg insulators on the end of each wire.

Does it perform better than the Firestik model? Hard to tell. Don't know any locals to talk to and DX contacts are still rare. (Remember, I'm running barefoot.)

I'll likely leave this up for a while. It's already getting too darn hot in the attic to be fooling with antennas and the such.

 

[fourstringburn]

Nice project! You made the correct choice by going to 1/4 wavelength wires instead of loaded whips.

Loaded whips may have a 50 ohm impedance but has inherent losses in the coil itself.

Typically a wire dipole like this won't be 50 ohms on the CB band using wire but more like 75 ohms. This is where you will learn about impedance matching antennas if you want to make it near perfect.

A good investment if you like to make antennas and really know what your antenna is doing is to invest in a good antenna analyzer. SWR meters don't tell the whole story and their accuracy is questionable.

A good one will set you back a good $250.00 or so, but I hated trying to borrow one when I needed it so I bought my own and can't get by without one now.

 

[The DB]

Typically a wire dipole like this won't be 50 ohms on the CB band using wire but more like 75 ohms. This is where you will learn about impedance matching antennas if you want to make it near perfect.

I don't know if it would be a perfect SWR match or not, but it will be lower than if it were a flat horizontal dipole's natural feedpoint impedance of around 75 ohms simply due to the angle of the legs... Not that SWR means much to me either...


The DB

 

[Captain Kilowatt]

A dipole is 75 ohms in free space. The actual impedance will depend on it's height above ground as well as proximity to surrounding objects.

 

[Riverman]

I do need an analyzer. Maybe for Christmas!

First tried hanging it flat but couldn't get the SWR under 1.6
The SWR with it inverted varies with which way it is turned. Am guessing this has to do with nearby objects. The Firestick model acted the same way.

 

[Beetle]

Okay, I put up a half wave wire dipole for comparison purposes. Made it out of a 10' electrical extension cord. An Inverted V Dipole calculator said each leg should be about 98 inches. That worked perfect. SWR is less than 1:1 on all channels without any adjustments.

I'll likely leave this up for a while. It's already getting too darn hot in the attic to be fooling with antennas and the such.

By definition, your SWR cannot be "less than 1:1". Your reflected power may well show as zero, but the ratio won't. 1:1 is as low as a ratio goes.

 

[Riverman]

By definition, your SWR cannot be "less than 1:1". Your reflected power may well show as zero, but the ratio won't. 1:1 is as low as a ratio goes.

Oops! You are correct, sir. I meant less than 1.1 to 1.

 

[Riverman]

For the connection I soldered the wires and covered them with heat shrink wire wrap and electrical tape. I then pulled them into a short piece of graphite tubing (a piece of an old golf club shaft) and sealed both ends with epoxy. This provides excellent strain relief and 100% waterproofing should I ever want to move the antenna outside. (Or in the event my roof leaks.)

The coat hanger is attached via a small hose clamp.

 

[Stellasstillarat]

A $50 cobra, $20 antenna, $20 meter and $20 in coax (just guesstimating). Why would a $250 analyzer be considered a wise or nesessery investment? Assuming his swr is double the listed reading (doubt it) I'd say his contract to Japan on 3 1/2 watts is an excellent job and he definitely sounds like he's enjoying himself and the hobby. I know operators that who spent $500 on an amp $350 on a cobra 2000/madison/2510 ect. ect. a $130 on a imax 2000/antron and hardware to install it 30 ft in the air and have difficulty making 1500 mile skip contacts. I'd bet less than 2% of cb operator's own an analizer and 90% of those don't know what an analizer is or what it's for and, I'm one of them. My swr meter says 1.1:1 on channel one and tops out at 1.4 at 27.6955. Been making contacts all over the world for four months now with little station issues (none swr related). Excellent job on your station my friend. Keep up the good work. P.s. I will do some research on the aforementioned analizer because I wanna lear but doubt I'd ever make a purchase.

Nice project! You made the correct choice by going to 1/4 wavelength wires instead of loaded whips.

Loaded whips may have a 50 ohm impedance but has inherent losses in the coil itself.

Typically a wire dipole like this won't be 50 ohms on the CB band using wire but more like 75 ohms. This is where you will learn about impedance matching antennas if you want to make it near perfect.

A good investment if you like to make antennas and really know what your antenna is doing is to invest in a good antenna analyzer. SWR meters don't tell the whole story and their accuracy is questionable.

A good one will set you back a good $250.00 or so, but I hated trying to borrow one when I needed it so I bought my own and can't get by without one now.