W7KF
Whitefish, Montana, USA
There are lots of designs for quarter wavelength vertical antenna systems. But, a quarter wavelength antenna on say 40 meters is a half wavelength antenna on 20 meters. So, while the antenna is easy to feed on 40, it's a more difficult proposition on 20.
For a multi-band vertical I find non-resonance to be a real asset. A coupler mounted at the antenna (where it belongs) will have an easier time matching the antenna to coax on multiple bands when the antenna is not resonant on any of them.
At my last QTH I ran a 27.5' vertical for many years. Why 27.5 feet? That works out to being a 5/8 wavelength on 15 meters and just a bit short of a ¼ wavelength on 40 meters. So, with a decent coupler and ground system, the antenna should radiate like a blowtorch on 40 through 15. It should also work on 60 and, to a much lesser extent, on 80 as well. (Note: A vertical that is longer than about 5/8 wavelength radiates a good deal of it's applied RF upward at a high angle. And, since NVIS propagation doesn't work much above 10 MHz that means a lot of the RF is wasted.)
So, when I started seeing a lot of excitement about the 43' verticals I decided I'd look into the matter. I assumed that the goal was non-resonance and sure enough 43' isn't resonant particularly close to any of the major ham bands. (It is close to resonant on the 60 meter band.) And, it turns out that 43' is just a bit longer than 5/8 wavelength on 20 meters. So, it should make for a good vertical on 80 through 20 while still producing contacts on 15 and even 10 meters.
Since I had moved to a new QTH and needed new antennas and since I spend most of my time on 80, 40 and 20 meters, I thought something in the 43' range might make for a good antenna for me.
But, first a bit of time with EZNEC and a spreadsheet was in order. Using these tools, I pondered the situation and ultimately came to the conclusion that what I really wanted was a 40' foot vertical. It seemed to me that the longer 43' verticals offered somewhat better performance on 80 meters but the vertical pattern suffered on 20 meters. And, I'm on 20 more than I'm on 80.
Now, I live in an area where there are a kadzillion deer. And, deer (especially bucks with their big antlers) can be a real problem for verticals that need guy ropes. The deer can easily get tangled in lightweight guy ropes and bring an aluminum antenna down to ground level. It's bad for the deer and it's not so good for the antenna. Thus, I felt I needed a non-guyed solution.
The other enemy is wind. I live in Montana and we sometimes get arctic winds that can really howl. But, those winds are not like the hurricane winds that plague the east and gulf coasts. I judge the deer, which are here every day, to be more of a threat than wind. A free-standing antenna is my choice.
My 27.5' antenna was just such a thing. Non-guyed, simply mounted to a 4" x 4" x 8' post which, in turn, was planted in concrete. And, that thing withstood some vicious Montana winter wind storms. But, a 40' tall antenna is another matter entirely. The search began.
While looking at options for aluminum I stumbled upon an antenna (DX Engineering MBVE-5 SAF-T-TILT™ HF Multi-Band Vertical Antenna) that was about the right size, had a nice mount system that allowed for easy access to the antenna element, and was specified to handle up to 92 MPH wind speeds in a free-standing configuration. Seemed like just the thing!
The DX Engineering antenna has two major innovations. First is the "SAF-T-TILT" mount system. They really thought this one through and it's a cool system. There is a video that shows how the thing works.
The second innovation is that they used 3 foot long sections of aluminum rather than the more conventional 6 foot sections. This causes the antenna to taper faster. Thus, the top element is 3/8" diameter where the top element of my 27.5' vertical was 1-5/8". This makes for lower wind load and seems like an idea worth testing. I ordered the bare bones sytem, just the mount and the antenna for a bit less than $200.
Next up was to figure out how to mount an antenna coupler at the base of the antenna. The DX Engineering system shows the coupler mounted horizontally, near the ground with at least two feet of feed wire from the coupler to the antenna itself. They also showed a radial plate mounted underneath the coupler, on the ground. It all seemed too complicated and I didn't like the idea of the long feed wire from the coupler to the antenna.
After some thought I came up with a different design. The basic idea was to mount a remote antenna coupler (a Harris RF-382A) to an aluminum plate that was, in turn, mounted to the antenna mount plate. That way, the coupler would be mounted with the coax and the control cable on the bottom near ground level and the RF lead from the top of the coupler to the antenna element would be only six inches long and horizontal. Plus, I decided that the coupler mount plate could also act as a radial plate. Of course, the whole thing would be controlled from the shack with a KF-382 coupler controller.
The only issue with this design was that the DX Engineering antenna mount plate is 3/8" thick and it would be somewhat challenging to mount the coupler plate to it. I'd need to use some angle brackets or come up with something. A quick trip to the Junque Box (which I will admit is somewhat unique) yielded a 1" thick piece of aluminum plate that was very nearly perfect in size being only an inch or two taller than the mount plate from DX Engineering. A quick look at the parts from DX Engineering confirmed that everything would still fit. A thicker antenna mount plate would allow mounting a 1/4" thick aluminum plate upon which I could hang the RF-382A and attach the radials. So, it was off to the shop to start cutting metal!
I used the DX Engineering antenna mount plate as a template, marked up the 1" thick plate and started making chips. In this picture I'm machining the slots for the antenna mount bolts.
And, here I'm maching a long slot that will help maintain a proper relationship between the mount plate and the 2" O.D. pipe that will be planted in a large batch of concrete out in the yard.
Here are the two new parts, the antenna mount plate and the coupler mount plate. I'm going to use electrical system ground buss bars to attach radials.
It's time to see if the parts will all fit together!
It looks like it will all fit together. Here it is, assembled on the bench complete with the RF-382A antenna coupler.
Next stop? The paint booth! OK, so I don't have a paint booth. I just haul stuff out into the driveway and use rattle can spray paints.
Shown above are the major parts of the antenna mount setup. Left to right are the antenna mount plate, two pieces from the DX Engineering system that I'll use and, on the right, the coupler mount plate. I've pre-drilled the coupler mount plate to accomodate either the Harris RF-382A or the Harris RF-351 coupler. I have one of each and would like to be able to use either -- that way I have a spare.
Now, it's time to plant the 2" O.D. pipe in a hole in the ground and mix concrete. 200 pounds of concrete ought to do. Then, the pipe gets a paint job to match the mount system. Here's a picture of the planted pipe, the assembled coupler mount system and the LMR-600 coax and the 10-conductor control cable for the antenna coupler.
Hmmm.. Perhaps a word about the conduit and related matters.
The conduit is 1" I.D. irrigation pipe that I picked up at Home Depot. It was a 300' long roll as the run from under the operating desk in the shack to this antenna site is 225'. Which is, incidentally, why I chose Times Microwave LMR-600 for the coax run. It's beefy and has very low loss even for such a long run.
Of course, the conduit must remain water tight and the only way water can get in is at the very end where the cables exit. I obtained plastic end caps and drilled them to just barely fit the LMR-600 and control cable. The two cables are a tight fit through the drilled openings. I also placed a rubber grommet or two inside the conduit (probably overkill). Here's a close-up shot just before assembly.
Once the grommets and plastic end cap are pushed (hammered actually) into the conduit a few coats of liquid electrical tape are applied. This should keep moisture from getting into the conduit. Later I'll place split loom tubing over the entire assembly to protect the conduit end and both cables from the elements.
With the cables in place, the 2" post planted and painted and the mount system finished it's time to put the whole thing together! Here's what it looks like without the radials, the coupler and the actual antenna element:
The next step was to install radials. Ugh. Laying radials isn't a lot of fun but it needs to be done. I've read an incredible series of articles by Rudy Severns (K6LF) and he has convinced me that 32 radials is enough at HF UNLESS your antenna is shorter than 1/4 wavelength. Then, more is better. Since I'll use this antenna on 80 meters where it is short, I'm planning on 64 radials. And, the extra radials won't hurt on the higher bands so why not?
I like to use 18 AWG magnet wire for radials. It's fully annealed rather than stiff and springy so it's easy to manage. 2500 feet ought to do.. [Fast forward a few days; the radials are in place and stapled down.]
Above you can see the 64 radials. Oh, and the split loom covering over the coax and control cables.
Next, there was the small matter of painting and assembling the 40' antenna. Did I mention that the DXE-MBVE-5 is actually just a little over 40' tall? I guess the normal length plus the two foot antenna lead normally required makes it a 43' antenna. But, since I decided that I wanted a 40' antenna I just didn't use all of the top 3/8" diameter section and didn't use a two foot antenna lead wire.
Anyway, I sanded, primed and then painted each antenna element. (Except, of course, for the four inches at the bottom of each element that telescopes into the lower section.) I like to paint my verticals so as to reduce the visual impact on the neighborhood.
Once painted the antenna was installed onto the system and walked up into place. The easiest part of the entire project! Here's what the final assembly looks like, looking toward Asia. (Are you a downhill skier? On the right side of this picture you can just see Whitefish Mountain Resort. That's why we live here!)
Here's the view toward Europe. By the way, this thing shouldn't work very well on 15 meters since it's taller than a 5/8 wavelength. But, it seems like I have a pipeline into EU on 15 meters! So much for all my fancy modelling and spreadsheet analysis..
And, here's the view toward South America. It's a close-up shot so you can see the various components. South America is not quite visible from here in Montana.
All in all, it makes for a tidy installation. Oh, and I finished it up JUST IN TIME! Here's what it looked like a few days after the final installation.
