DXE Catalog is the “Erector Set” for Antennas
DX Engineering makes it fun to prototype antenna ideas with their parts.
They deal with aluminum tubing in a big way. I love my 43 foot antenna from them. It was a natural
first place to go for a supply of antenna components.
Pleased with my experience using the Resin Support Blocks for my Hex Beam and TV Antenna, I
made sure to consider them for this project.
DX Engineering also sells rectangular plates for use in the junction points of beam antenna elements
and boom. Thinking their small version was 1/4 inch aluminum plate, I added that to my wish list.
After some time with simulations and with their web catalog handy, I came up with this design…
Figure 1 – Asymmetrical Hatted Dipole Antenna
KX4O-000049.pdf
Full size prints available.
Contact kx4o@hamradio.me for details.
Brand new parts for this antenna assembly, including the $50 speaker stand, will set you back about
$250… more than a little, less than a lot. Those with existing aluminum stock can likely reduce
cost.
Tripod for the Portable HF Antenna
One major premise of this design is the use of a commercial speaker stand from the music/sound
reinforcement industry. A tripod with its various angles, stress points, etc. is not an easy thing to
design and make. You don’t have to because the music industry offers quite an assortment of sturdy
models. Speakers are heavy things so these speaker stands already include engineering to make
them plenty strong enough for this lightweight aluminum antenna. A speaker stand was a
“nobrainer” for this project. Fortunately, I still have a couple stands from the “rock band” days.
With the prototype design more or less complete I made an order to DX Engineering and dug out
my speaker stand. This stand, by the way, is the same make and model used in the Hoverman
“Superbowl” TV Antenna.
Many speaker stands have 1-3/8 inch (~35mm) masts plus an optional plastic sleeve to
accommodate speakers with 1-1/2 inch (~38mm) sockets. The key feature of my stand is the unique
reversible upper section. This is 1-1/2 inches diameter for most of the length with one end narrowed
to 1-3/8 for about 6 inches. This allows the stand to interface with either size speaker socket simply
by flipping this upper shaft over. This is a big advantage for us because it provides a nice long 1.5
inch mast to interface with the rest of the antenna. Here is a link to the manufacturer of this stand…
Manufacturer information on SS7761B Speaker Stand
Other nice features of this stand are adjustable height, up to 80 inches, and a locking pin to secure
the mast. The antenna’s weight is much less than most speakers so you can rest assured the locking
pin isn’t really necessary, but is there for the cautious. The adjustable height is a great feature to
have for any antenna.
Shop around. Despite the news to the contrary, the economy is not in good shape and the various
music equipment suppliers are in savage competition for your dollar. Amazon reveals this quite
well…
On Stage SS7761B Music People SS7761B Tripod Speaker Stand
You should be able to get this stand for a very good price and with little to no shipping costs.
Note, the On Stage stand is made of aluminum and will resist corrosion. However, the small
hardware parts are steel and will quickly rust outside. You can replace the parts with stainless steel
or coat them with something like oil, WD40 or maybe paint. I am eager to hear how others handle
this.
Parts arrival day
When the DX Engineering order arrived I opened the package to find aluminum tubes, resin support
blocks and one rectangular plate. I was very interested in the plate so I picked it up first. Wow light.
Wait… this wasn’t aluminum. It’s a piece of black plastic.
Oops… in my haste I did not read the description on DX Engineering’s web site closely. Sure
enough I ordered a plastic plate. However, it was 1/4 inch thick and seems quite sturdy. After some
thought I decided to use it as the back bone of the antenna. Here is the drill drawing to convert this
piece for use with this antenna design…
Figure 2 – Vertical Dipole Antenna Support Plate
KX4O-000050.pdf
Thinking it was 1/4 inch aluminum I was prepared for quite a drilling task. I even purchased a
special bit.
It all turned out reasonably well. Let’s have a look…
Portable HF Antenna Prototype in Driveway
The driveway became my test area.
Figure 3 – Asymmetrical Hatted Dipole Protoype
Figure 4 – Tripod side of Asymmetrical Hatted Dipole Support Plate
Figure 4 shows the tripod side. The DX Engineering resin support blocks do a fantastic job of
holding on to the speaker 1.5 inch diameter stand.
Figure 5 shows the tube side of the support plate…
Figure 5 – Tube and feed side of portable hf antenna Support Plate.
Note the resin support blocks for the vertical aluminum share the 1/4-20 hardware with the tripod
blocks on the other side. In this way, the support plate does not carry the load of the vertical as it
transmits its load directly to the tripod mast.
Figure 5 also shows the absolutely essential balun. You need a good one as this design encourages
current flow on your feedline. Drawing KX4O-000049 has some suggestions. In this particular case
the RG316 balun is more than sufficient for my planned QRP operations. Note also, the lower two
bolts holding the tripod and vertical aluminum serve a third purpose of feed/balun mount points.
Figure 6 – Portable HF Antenna in “tuning” position
Measurements confirm this portable hf antenna has enormous bandwidth
The antenna takes some fiddling to find the 50 ohm sweet spot, but it falls right in place once found.
Here are measurements for each band after experimentally adjusting the radial and vertical
lengths…
Figure 7 – SWR of Asymmetrical Hatted Dipole
Key points to know about Figure 7…
The x-axis is logarithmic.
The legend reveals the vertical height above the radial “H” and radial spoke length “R”
dimensions resulting in each SWR plot. These are also in the KX4O-000049 Drawing.
The dashed lines are the SWR values from simulation for comparison.
Other tests reveal the ground does have some effect and broadens the bandwidth from 7% to about
10%. That’s clearly loss in the soil and not a surprise. These measurements were made in haste as I
was marking the various tube settings with a sharpie. The good news is I could easily, very very
easily, achieve close to 1:1 if I spent more time. A Return Loss of 25 dB or more is well within
reach of this antenna topology.
As you can see, the bandwidth is amply wide enough to cover each band handily.
First Field Test at Field Day 2013
Where better to conduct initial field tests of a portable HF antenna than at Field Day. I was in
charge of the GOTA station and made this antenna the 20m aerial.
Figure 8 – Field Day test for the Portable HF Antenna
I did replace the RG316 balun with a larger one for piece of mind at 100 watts. I also guyed the
assembly with tent stakes and Dacron; The speaker stand has enough tie points to make this easy.
Did it work?
Yes it did and here are my sons making 20m contacts to the West from Virginia using only this 0
dBi antenna and about 100 watts…
GOTA, 20m and the Asymmetrical Hatted Dipole
Thank you boys. You helped test two new antennas this Field Day… the other being the mastless
40m dipole.
This Vertical HF antenna is portable – sort of
This picture shows how the nested aluminum tubes and the tripod extension collapse enough to fit
into one of my son’s old baseball bags.
This is a portable HF antenna.
The tripod of the speaker stand won’t fit into this bag. It is very light, however, so isn’t hard to haul
a great distance. Remember, the speaker stand is designed with the poor band roadie in mind.
The aluminum antenna element tubes take up less length if you don’t nest them, or by removing the
clamps and nest them fully. Your choice. I leave my clamps on to make setup and break down
quick. The longer vertical section is in the open end bat storage pocket.
I leave the speaker mast portion of the speaker stand on the plate, but with the mast slid up to be
parallel and opposite of the vertical aluminum…
Tripod mast in the “stowed” configuration
I should note the Bravo Antennas from Schiller are more compact and portable than this prototype.
Summary
So far this antenna is a keeper. Favorite points include:
Robust – The DX Engineering components and commercial speaker stand combine to form
a rock solid assembly that, other than potentially tipping over in the wind, you don’t have to
worry much about.
No Fuss Design – The lack of series or shunt reactive components keeps the bandwidth very
broad with predictable, achievable and reliable behavior. Yes, there are still interactions with
the soil beneath, yes the two radials are more easily electrically perturbed than, say, nine
radials, but nothing here demands critical dimensions or super tight tolerances.
No Loss Design – Additional loss from series or shunt reactive components, however small
they might be, are zero in this design.
Single band AND Multi band – This is a single-band-at-a-time antenna. You must change
element lengths to change bands. Clever multi-band feed designs are certainly possible with
this antenna assembly. Where I have a choice, I lean towards simpler designs… less to
break. I don’t mind the time it takes to change bands manually, but others might and that’s
perfectly fine.
Yagi Ready – Because the elements are continuously tunable from about 13 MHz to well
past 30 MHz, the prospect of arraying two or more of these assemblies, in Yagi-Uda
fashion, is exciting. A future article on simulations of this antenna will explore this.
Feedpoint where you need it – The bottom feedpoint is more convenient than traditional
center-fed half-wave vertical dipoles… such as the “I” styles.
Buy, Make and Take – This design’s strength is its simplicity, portability, availability and
modest cost.
Another choice for you – This portable realization of the Cebik, et al., asymmetric hatted
vertical dipole is a worthy alternative choice to many freestanding portable hf antennas
including the “I” shape symmetrical vertical dipole and the various Buddipoles.
Potential Uses of the Asymmetrical Hatted Vertical Dipole
This is a well behaved portable HF antenna for 20m – 10m with the following potential uses…
ARRL Field Day,
Portable field work including lighthouses, IOTA, parks, special events, etc.,
Camping,
HOA restriction avoiding “Lawn” antenna,
Summits on the Air (SOTA). Yes, this might be a stretch, but certainly possible.
Conclusion
If you need a freestanding 20-10m antenna that’s easy to build, easy to tune and relatively easy to
carry, this design is worth consideration.
The next posts report results of using it at the beach for some lighthouse and IOTA work.
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