Antenna Basics

A Personal Journey

 

Four years ago I decided to fulfill a childhood dream. I had been a Shortwave Listener at that time, and even though I knew no Hams personally I aspired to join their ranks. I devoured any ARRL book I could find in my neighborhood Library, and even scrimped and saved to buy some for myself as well as a subscription for QST as an associate (unlicensed) member of the American Radio Relay League.  Those dreams didn’t turn out well at the time and, as often as it does, the real world required that I put this particular dream on indefinite hold. Fast forward many years and I decided to finish what I started so many years ago. In a relatively short matter of time I was an Amateur Radio Operator, albeit one with no radio of any kind… But radios can be selected and easily purchased – what in the world would I do for an antenna!

 

ARRL publications should warn the unwary that this sounds simpler than it often is. Having read the Public Relations version of Amateur Radio from the pages of 1960’s QST articles I believed that we were all one big fraternity, that with my FCC ticket in hand all I had to do was  ask and a bunch of Hams would fall out of a little car like diminutive clowns do in circuses and we would have an almost “Amish” Barn Raising, albeit with an antenna instead. I had foolishly forgotten that I did not live in OZ, but good old Brooklyn, whose motto should be something along the lines of “What’s In It For Me?”. No, getting anything but the most compromising of antennas would be a journey over 3 ½ years and a heck of an education!

 

What I had to do, was learn antenna theory as well as I possibly could.

 

What I wanted was an antenna system capable of operating from 80 Meters to 70 centimeters. Something that was the least of a compromise as I could design. Something that would require little to no tweaking nor maintenance. Something with some decent elevation. Something durable, but not too heavy or requiring skilled installers. Something that didn’t require a bottomless wallet too would be nice! I got dubious offers of help, but they always seemed to come with the requirement that I use specific types of antennas that did not strike me as the best for my needs. One specific antenna was a full size G5RV antenna that is 102 feet long and a Hex Beam that is very nice for the upper HF bands but rubbish below 20 Meters.

 

One of my personal pluses and minuses is that I own a two family attached house, so I don’t have to ask anyone for permission to install anything on my own property.  That was the big plus – the minuses are the limited space of urban lots and being wary of scaring the neighbors. The entire lot for the house is 100 x 20 feet. The front 25 feet are taken up with a stairway and a driveway and a basement entrance, with not even a tree in the front of my property, proper, so the front of the house can’t be used. That leaves my flat roof approximately 25 feet above ground level, measuring  50 x 20 feet, as well as my backyard that’s 25 x 20 feet. So I have 75 x 20 feet  to play with – nothing more!

 

So, what did I come up with in the end?

 

For my UHF/VHF needs I decided upon a Comet GP-6 dual band antenna:

GP-6

And for the 80 Meters to 10 meters of the HF Band I chose an Alpha-Delta DX-CC fan dipole:

AD DX-CC

Alpha Delta DXX-CC

But where to put it exactly, how to get it up there and how to keep it up there – that’s the question!

The only place to plant the center of all this is on my flat 50 x 20 foot roof. First, consider a sturdy base – an Easy Up 5 foot heavy duty tripod.

EZ-48-5AW

Easy Up EZ-48-5AW

Screwed down with six long lag bolts to the roof (into the rafters, or the joists). Then stick a 34 foot Rohn Telescopic Antenna Mast and secure it a foot or so above the base of the tripod using the two sets of three set bolts of the tripod (the mast is small enough to be shippable by UPS at a MUCH lower cost than freight costs).

Rohn 9H50

Rohn 9H50

Clamp the Comet GP-6 at the top, with a coil of LMR400 as a strain relief so that the weight of the coaxial wire doesn’t pull the cable from its connector, and then consider how to mount the fan dipole…

 

The simplest solution would be just to bolt it to the top of the mast, but simple is almost never the best solution. I chose to hang the center support for my fan dipole on my guy rope (we’ll get to guy ropes shortly), using a maritime grade stainless steel pulley so that the fan dipole can be raised and lowered without bothering the Rohn collapsible mast. I anchored it near the base with a lead weight so that the wind could “bob” it a little, but past a certain point of loose rope it is securely tied to the base of the mast. You don’t want coax to just hang down from the connector – you’ll just be asking for it to work itself loose over time. So I found a strain relief bracket from DX Engineering to relieve the weight of coaxial cable. I also made my own RF Choke with 5 Mix 31 ferrite clamps in a row and covered the group with heat shrink tubing which has made them pretty much waterproof (these kits can be found many places, I found mine at Palomar Engineers).

 

One inch wide copper strapping was bolted to the tripod and dropped down in the rear of the house where it was grounded to the cold water pipe feeding the backyard water hose (these are good old copper pipes, no plastic segments here!). So, my grounding was covered (although if you get two Hams together, you will invariably hear three different theories regarding what proper RF grounding should be)!

 

So, that was the plan for the antennas themselves, but how was I going to make sure that they stayed where I wanted them to? Why guy rope and mountaineering rigging, of course!

 

First guy rope – wire would just be too difficult to get untrained people to work with. Thankfully rope technology has advanced thru the years. I chose an Italian manufacturer of very durable guy rope – Mastrant. Their 5 mm (3/16th of an inch) rope has a tensile strength of more than 1,100 pounds (they sell stronger stuff and thicker stuff, but you can only over engineer so much!). No matter how strong, UV resistant and generally durable rope can be made, abrasion is its enemy. By using stainless steel parts at any point that the rope might otherwise have abrasion damage this can be remedied!

aaaaabaacaad

The tools of the trade…

 

I designed two pairs of guy ropes – one towards the top of the mast, the other in the middle of the mast, connected to the four corners of the roof. The rope was calculated thanks to my old high school trigonometry lessons, measured thrice, cut once (with more than enough “extra” length if some problem occurred – it is far easier to decrease a rope’s length than to increase a rope’s length!).  Buckmaster Line Grip was utilized to keep the guy ropes reasonably taut and they were secured to the four corners of the roof with lag eye screws. The same method was used to secure the ends of the fan dipole, but only one end was secured to the front of the roof. The other end is secured at the backyard.

All the rope was folded to prevent kinking and cable ties kept them that way until the ropes were installed. All attachment points were clearly labeled and a short set of bullet points and diagrams were supplied to the roofers that were kind enough to do this after they installed my newest roof cover (some times it’s a good thing to be a bit overly focused on a design).

aae

aaf

 

 

 

 

 

 

So, what does it all look like? Well, I’m glad that you asked:

house

There she is! In all her beauty!

 

How does she work? Well, better than some and worse than others. As you would expect.

 

So, the next time you ask for help and get told to throw a random wire out your back window, give ‘em a Bronx cheer and dream for something finer!

 

Good luck with your dream!

– Your Editor – [Roy, AC2GS]