Residence Antenna Plan

My wife and I live in Phoenix in a 1960 city-size lot. I mention the year because city lots have shrunk in the past couple of years and our 100’x105′ property seems large by comparison.

But with the sparsity of trees in Phoenix and keeping in mind that 80 meter wavelength I’d like to be able to use someday, our 1960 lot doesn’t seem that big or antenna friendly anymore.

On the plus side, the neighborhood has been here 50 years and the CC&Rs are pretty much ignored as long as violations aren’t too flagrant. Indeed, there are several modest antenna towers within a couple of blocks that were almost certainly erected with the current CC&Rs in place.

But I’m not a tower and beam kind of guy, or at least, not yet.

Instead, I like the flexibility and ease of putting up wire antennas, and then taking them down and putting them up in a new configuration a few months later, and then changing them yet again next year.

50′ Vertical



Tower-candidate at Left

(Click for larger)

To my distinct advantage, I have a 50′ palm tree about 1/3 of the way back from the street abutted to the neighbors property. The bottom of that tree is no more than 30′ of RG-8X from where I have my operating position and the large screw eye, pulley, black dacron rope and an extra $10 are just waiting for the next time we have someone climb and trim that tree and, while they’re up there, attaching that near the top and then securing the other end of the looped rope near the bottom.

That arrangement will then easily handle a 1/4 wave vertical for 40M that can be run up or down the tree as desired.

But the counterpoise, well, that’s a head scratcher. There are several obstacles to a permanent or even semi-permanent installation. First, there’s the neighbors concrete driveway right next to the tree. Second, there’s the grass in my yard that has to be cut every Saturday for eight months of the year. And third, there’s a concrete block fence from the house to the side of the yard that would be in the way of any ground radials headed back along the property line.

Consequently, the system of radials for that vertical antenna is probably going to receive a lot of experimenting. There’s a simple one in the ARRL’s Low Power Communication book (page 6-6, figure 6-2) made from a 50′ length of 5-conductor rotator control cable I’m considering. The text says its for an end-fed which is certainly what my vertical will be and although that one cable will only be going one-way, I’ll probably start with that. The antenna and counterpoise will be put up (and out) to operate but then packed up (down and in) at the end of the evening.

Kaboom!

“Put it up” and “take it down” sounds like a lot of bother but two years ago a trio of palms 75 feet away (and still in my yard) took a lightning strike. The top two feet of one was split and burnt and although the other two showed no damage, all three had their roots entwined and, a couple of weeks after the strike, it was apparent all three palm trees had been killed.

And while it’s also true that there’s a buried power cable belonging to the electric utility ten feet from where those trees stood and that the power cable may have had something to do with that particular strike — after the strike the ground was “puffy” between the trees and where the cable is buried — there’s no denying the fact that we do get lightning strikes in residential Phoenix.

Putting up and then taking down the 50′ vertical for each use seems prudent.

Portable Operation

That combination of antenna wire and counterpoise will also suffice for portable operation with the addition of something for height — a tree or sectioned fiberglass pole. Admittedly, I’m unlikely to find a sectioned fiberglass longer than 25-30 feet but, even so, that would be a good height for either one end or the middle of the antenna.

And with some batteries and my QRP (low power) radios, I want to put on my hiking boots and “activate” some peaks in SOTA (Summits On The Air). You’ll find some good videos at YouTube. (There’s no group for this call area — I’ll have to check into taking on that job. I could do that.)

For that as well as the front-yard vertical, I’ll also need a feed-point tuner. So my first purchase to be assembled was a ZM-2 ATU (Antenna Tuning Unit) kit, suitable for QRP power levels.

The vertical will be fun and afford lots of opportunity for experimentation but it’s not likely to be my first antenna. Scaling that palm is well beyond my ability (and guts) and hiring a “cherry picker” is too expensive. The tree trimmers can do it but the antenna will have to wait for “the little guy that goes up the tree” whenever that might be.

Over the Thanksgiving holidays, I’m going to go stealth.

40M/20M Dipoles

I’m almost done with assembly of the JUMA RX-1 DDS receiver and need a “sky hook” by which I can start listening.

In particular, I want to listen to the 40M band on that radio to practice my CW copy so I need antennas for those bands “real soon.” But, walking around the house and looking, there just aren’t any convenient trees for dipoles in my yard. And the power lines across the back of the lot and the drop from there to the house are an important safety consideration, too.

Outside dipoles just don’t seem to be a viable option.

But what about inside, inside the attic?

Yes, I know, that’s not a very good place for an antenna. The radiation pattern is going to be nearly straight up with those wires barely 15′ off the “ground” at the feedpoint. And because it will be strung diagonally inside the attic in order to get the needed 66′ for 40M, the ends will be even lower.

But dipoles are “stock and trade” in this hobby and I’ve put them up and taken them down many, many times. They are easy to construct and install, easy to tune, and just as easy to take down when a better solution comes to mind.

In my initial thinking about this, I planned to build 20M resonant traps and install a 40/20M trapped dipole. But at a recent meeting of the AZScQRPions, another ham suggested simply attaching the 20M and 40M dipoles to the same feedpoint but skewing them out in an “X” shape. And while it is true that the pattern might be a bit odd, well, all the energy is going to go pretty much straight up so who cares about “pattern”? Up is up.

So, that’s now the plan. I’m collecting parts for my 40M and 20M in-attic X-dipoles connected to a common feed point. I’ll feed with the RG-8X pulled up from the operating position through the attic and connecting to a coax balun at the feedpoint. And after tuning for both bands, hopefully I’ll see a survivable SWR and have a no-switch-needed dual band antenna.

Hmmm, tuning. I’ll need the ZM-2 ATU, a transmitter and wire cutters for that but the JUMA TX-1 won’t be finished for a while. I’ll be listening before the antenna is tuned. Guess I’ll have to live with that.

Maybe someone in the AZScQRPions will have an antenna tuner I can borrow. Note to self: Check calendar and mark the next meeting of that group.

That’ll cover my initial forays on 40M with the RX-1 and, when the PSK-20 rig is assembled, I’ll have something to use on 20M, too.

But 80M, well, that’s a tougher challenge still.

80M Horizontal Loop



Final Plan

Helicopter View

(Click for larger)

[Google-Earth image]

Or that’s what I thought until, at that same AZscQRPions meeting, someone commented they had a long loop strung around the edge of their property on top of the concrete block fence.

Hey, I’ve got one of those!

The fence encircles slightly more than half of our property. Measuring the linear length, I paced off 125 yards around the top of the fence which, even if I’m off by 10%, is more than 80 meters and, with a few adjustments, I might have the right distance for a full-wave. To anyone who walks up and looks, it’ll look like an electric fence, a single wire standing off from the concrete block on insulators. (I’ll position it so it’s out of sight from the street to keep the wife happy.)

But I need to figure out, even running QRP with no more than 5 watts, are there likely to be any voltages that could be hazardous to someone touching it? If so, the loop in that finger-touchable location would be a “no go”.

I know Ohm’s Law, of course, and can easily convert 5 watts into volts and amps if I know the impedance, but that latter value isn’t a constant across the length of an antenna. Indeed, in a dipole, it’s extremely high at the ends and, on a loop, it’s going to have hi-Z and low-Z nodes — but how high is high because that’s where the voltage is going to be developed? That’s where it could be significant.

Well, that’s part of the fun of this hobby, learning things and then finding solutions to problems.

Okay, so where’s my book on antenna theory?

And who put away my slide rule?

Addendum

As an afterthought, I paced off an “under the eaves” horizontal loop — 100 yards, much closer to the desired 80 meter length. And an antenna there would be out of reach where I wouldn’t need to worry about people’s fingers and voltages along the antenna (at QRP levels)…

And it’d be a lot easier to attach the antenna wire to the wood than to concrete.

Hmmm.

(This is fun!)

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