Tech
The DX Commander Antenna
Callim, M0MCX the “DX Commander”
My Vertical Antenna & Common Mode Choke Build –
Part 2
Vertical Antenna:
In last month’s newsletter, I wrote about assembling my DX Commander vertical antenna for Field
Day at the ARC. It was something I threw together in the middle of the night, and managed to get
operational on just a couple of bands for Field Day Sunday. It was held together with bits of
electrical tape, and I only got it to tune on 20m out of sheer luck. It seemed to work well, but needed
a lot more work to finish the build.
I set my sights on the Ohio QSO Party in August. I wanted to finish the build and make it field-ready,
so it would just pop-up and be ready to go. This would mean finishing all the various band elements,
tune each band, and replace all the temporary bits of electrical tape with proper heat shrink and
fastening clips. I wanted it to be easy to assemble, disassemble, and store – making it my go-to
antenna for portable operations.
For those not familiar with the DX Commander, it is described by the inventor as a Fan Dipole turned
vertical. Think of a typical multi-band Fan Dipole antenna. Its feed point is in the middle, and there
are elements extending ¼ wavelength left and ¼ wavelength right of the feed point. Turn it vertical,
and bring the feed point down to ground level. Those elements that were extending right of the feed
point are now reaching up in the air. Those that were to the left of the feed point are now spread
out as ground radials. And just like the Fan Dipole, It uses ‘spreaders’ to keep the radiating elements
separated.
The antenna is built around a telescopic graphite mast that extends 10m tall (that’s 33 feet or
approx. ¼ wavelength for the 40m band), with plastic discs at key points acting as spreaders to keep
the radials in position. Each time you deploy the antenna, you need to attach the elements for the
bands you want to operate. It supports up to 6 elements at once.
When you first build the antenna, you cut bulk wire to the required lengths for each element,
including: 10m, 12m, 17m, 20m, 30m, 40m (which also supports 15m as a ¾ wavelength), and 80m.
The instructions say 30m and 80m are mutually exclusive – pick one or the other as you assemble
the antenna.
To make assembly quick and easy, I printed labels for the posts on the radiating base, the holes on
each spreader, and the end of each radiating wire element. I just didn’t like the paper labels on the
wire, and wanted to use something more durable. I decided to use numbered bracelet beads
instead (see Figure 1). I used heat shrink tubing to hold them in place (see Figure 2). This makes it
easy to attach the elements correctly (see Figure 3).
Figure 1
Figure 2
Figure 3
To hold each element in place, the kit comes with a number of short elastic cords and clips. To
prevent the fiberglass mast from collapsing due to tension or moisture, several hose clamps are
provided (with plastic tubing to protect the finish on the mast). Assembly would normally require
placing each of these components on the pole one-by-one in the correct order. But I found that I
could loosen the hose clamps, and leave everything in-place on the collapsed pole (see Figure 4).
That includes all the cords and clips as well. I purchased a dedicated nut driver for the hose clamps,
and keep it in the go-bag. To assemble, I just start extending each fiberglass element (smallest to
largest), twist into place, and tighten the hose clamps at each join. I then run the wire elements up
the pole where the clips are waiting to receive them.
Figure 4
Tuning was the last step. As with any Fan Dipole, the adjustment of one element tends to have an
effect on the others. So there is a lot of trial and error. Adding the 80m element has the most
significant impact to other bands, so it was critical that I include that during my tuning effort. If you
choose to attach it, the 80m element is strung up as an inverted L. You need a high support (tree or
line of some type) to hold up the far end. That makes raising and lowering the mast more effort, and
you have to do that several times during initial tuning.
I tend to cut elements long (you know, ‘just in case’), so I needed to shorten each one a bit. Using a
RigExpert AA-600 analyzer, I measured SWR across all the bands used in the Ohio QSO Party (see
Figure 5). I was surprised to find 80m under 3:1 across the entire band. That means I can do both
phone and digital modes down the road, which I really want. 40m, 20m, and 15m (the money bands)
all came in below 2:1. As expected, 10m doesn’t want to be under 3:1 across the entire band. I may
be able to get closer with more adjustment. But I stopped tinkering when all the target frequencies
for OH SQL Party were around 1.5 or lower.
Figure 5
Overall, I’m very happy with the result. Yes, it does take more time to raise the antenna when you
are dealing with the 80m inverted L. And yes, there are a lot of bits and pieces to deal with. But
having all bands 80-10 available in one go-bag is really nice to have. And having a vertical does give
you an option for low take-off angle and more potential for DX contacts.
As for the Ohio QSO Party, we ran into more issues with multi-station interference at the ARC. We
were also limited to one station/mode per band at a time. As such, I didn’t get to put the DX
Commander to a full test. I’ll leave that for a nice fall day, when I get the urge to go play radio at a
park or open field.
Super-Choke
Here is a quick update on the Common Mode Choke I built in last month’s newsletter.
If you recall, I had created a form to make the choke, and managed to get 8 passes of LMR-400
(equivalent) coax through 2 sets of 3 toroids (see Figure 6). I stopped the build when I struggled with
soldering on the PL connectors. The solder kept balling up on the iron’s tip, and wouldn’t flow into
the connector.
Figure 6
The Messi and Paoloni Evolution PL259 connectors I’m using are not typical
(https://messi.it/en/catalogue/rf-coax-connectors/uhf-pl259-male/10mm/solder.htm). The tip is
soldered inside the body of the connector, not at the actual tip. The hole is very tiny, and the solder I
was trying to use was oversized for the job. The same is true for the female SO-239 connector. So, I
purchased some solder flux and small diameter solder. My soldering skills are still terrible, but I did
manage to get the job done. I went with male and female connectors on the choke, so I wouldn’t
need to use a barrel connector to insert it between a radio and the feed line.
Has it made a difference? Well, no – not yet. I used it at the Ohio QSO Party, but the issue there
wasn’t caused by common mode current on my feedline. I have a lot of QRM at home, but haven’t
seen any improvement with this choke alone. I still need to place chokes on the power and
computer connections to the radio, add a common mode choke out at the antenna feed point, and
ground the coax at entry of my house. Then I need to add chokes to all the problem devices
throughout the house. In other words, I wouldn’t expect one piece of the puzzle to solve everything.
I have a lot of work ahead of me.
If you want to read more on Common Mode Chokes, here is the guide I followed from Chuck
Counselman W1HIS.
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
- Mike W8MDC
Tech
The DX Commander Antenna
Callim, M0MCX the “DX Commander”
My Vertical Antenna & Common
Mode Choke Build – Part 2
Vertical Antenna:
In last month’s newsletter, I wrote about assembling
my DX Commander vertical antenna for Field Day at
the ARC. It was something I threw together in the
middle of the night, and managed to get operational
on just a couple of bands for Field Day Sunday. It
was held together with bits of electrical tape, and I
only got it to tune on 20m out of sheer luck. It
seemed to work well, but needed a lot more work to
finish the build.
I set my sights on the Ohio QSO Party in August. I
wanted to finish the build and make it field-ready, so
it would just pop-up and be ready to go. This would
mean finishing all the various band elements, tune
each band, and replace all the temporary bits of
electrical tape with proper heat shrink and fastening
clips. I wanted it to be easy to assemble,
disassemble, and store – making it my go-to
antenna for portable operations.
For those not familiar with the DX Commander, it is
described by the inventor as a Fan Dipole turned
vertical. Think of a typical multi-band Fan Dipole
antenna. Its feed point is in the middle, and there
are elements extending ¼ wavelength left and ¼
wavelength right of the feed point. Turn it vertical,
and bring the feed point down to ground level.
Those elements that were extending right of the
feed point are now reaching up in the air. Those
that were to the left of the feed point are now
spread out as ground radials. And just like the Fan
Dipole, It uses ‘spreaders’ to keep the radiating
elements separated.
The antenna is built around a telescopic graphite
mast that extends 10m tall (that’s 33 feet or approx.
¼ wavelength for the 40m band), with plastic discs
at key points acting as spreaders to keep the radials
in position. Each time you deploy the antenna, you
need to attach the elements for the bands you want
to operate. It supports up to 6 elements at once.
When you first build the antenna, you cut bulk wire
to the required lengths for each element, including:
10m, 12m, 17m, 20m, 30m, 40m (which also
supports 15m as a ¾ wavelength), and 80m. The
instructions say 30m and 80m are mutually
exclusive – pick one or the other as you assemble
the antenna.
To make assembly quick and easy, I printed labels
for the posts on the radiating base, the holes on
each spreader, and the end of each radiating wire
element. I just didn’t like the paper labels on the
wire, and wanted to use something more durable. I
decided to use numbered bracelet beads instead
(see Figure 1). I used heat shrink tubing to hold
them in place (see Figure 2). This makes it easy to
attach the elements correctly (see Figure 3).
Figure 1
Figure 2
Figure 3
To hold each element in place, the kit comes with a
number of short elastic cords and clips. To prevent
the fiberglass mast from collapsing due to tension
or moisture, several hose clamps are provided (with
plastic tubing to protect the finish on the mast).
Assembly would normally require placing each of
these components on the pole one-by-one in the
correct order. But I found that I could loosen the
hose clamps, and leave everything in-place on the
collapsed pole (see Figure 4). That includes all the
cords and clips as well. I purchased a dedicated nut
driver for the hose clamps, and keep it in the go-
bag. To assemble, I just start extending each
fiberglass element (smallest to largest), twist into
place, and tighten the hose clamps at each join. I
then run the wire elements up the pole where the
clips are waiting to receive them.
Figure 4
Tuning was the last step. As with any Fan Dipole,
the adjustment of one element tends to have an
effect on the others. So there is a lot of trial and
error. Adding the 80m element has the most
significant impact to other bands, so it was critical
that I include that during my tuning effort. If you
choose to attach it, the 80m element is strung up as
an inverted L. You need a high support (tree or line
of some type) to hold up the far end. That makes
raising and lowering the mast more effort, and you
have to do that several times during initial tuning.
I tend to cut elements long (you know, ‘just in case’),
so I needed to shorten each one a bit. Using a
RigExpert AA-600 analyzer, I measured SWR across
all the bands used in the Ohio QSO Party (see Figure
5). I was surprised to find 80m under 3:1 across the
entire band. That means I can do both phone and
digital modes down the road, which I really want.
40m, 20m, and 15m (the money bands) all came in
below 2:1. As expected, 10m doesn’t want to be
under 3:1 across the entire band. I may be able to
get closer with more adjustment. But I stopped
tinkering when all the target frequencies for OH SQL
Party were around 1.5 or lower.
Figure 5
Overall, I’m very happy with the result. Yes, it does
take more time to raise the antenna when you are
dealing with the 80m inverted L. And yes, there are
a lot of bits and pieces to deal with. But having all
bands 80-10 available in one go-bag is really nice to
have. And having a vertical does give you an option
for low take-off angle and more potential for DX
contacts.
As for the Ohio QSO Party, we ran into more issues
with multi-station interference at the ARC. We were
also limited to one station/mode per band at a time.
As such, I didn’t get to put the DX Commander to a
full test. I’ll leave that for a nice fall day, when I get
the urge to go play radio at a park or open field.
Super-Choke
Here is a quick update on the Common Mode Choke
I built in last month’s newsletter.
If you recall, I had created a form to make the choke,
and managed to get 8 passes of LMR-400
(equivalent) coax through 2 sets of 3 toroids (see
Figure 6). I stopped the build when I struggled with
soldering on the PL connectors. The solder kept
balling up on the iron’s tip, and wouldn’t flow into
the connector.
Figure 6
The Messi and Paoloni Evolution PL259 connectors
I’m using are not typical
(https://messi.it/en/catalogue/rf-coax-
connectors/uhf-pl259-male/10mm/solder.htm). The
tip is soldered inside the body of the connector, not
at the actual tip. The hole is very tiny, and the
solder I was trying to use was oversized for the job.
The same is true for the female SO-239 connector.
So, I purchased some solder flux and small diameter
solder. My soldering skills are still terrible, but I did
manage to get the job done. I went with male and
female connectors on the choke, so I wouldn’t need
to use a barrel connector to insert it between a
radio and the feed line.
Has it made a difference? Well, no – not yet. I used
it at the Ohio QSO Party, but the issue there wasn’t
caused by common mode current on my feedline. I
have a lot of QRM at home, but haven’t seen any
improvement with this choke alone. I still need to
place chokes on the power and computer
connections to the radio, add a common mode
choke out at the antenna feed point, and ground
the coax at entry of my house. Then I need to add
chokes to all the problem devices throughout the
house. In other words, I wouldn’t expect one piece
of the puzzle to solve everything. I have a lot of
work ahead of me.
If you want to read more on Common Mode Chokes,
here is the guide I followed from Chuck Counselman
W1HIS.
http://www.yccc.org/Articles/W1HIS/CommonMode
ChokesW1HIS2006Apr06.pdf
- Mike W8MDC