(c) 2020 DX Commander Limited - Page 4
Now, completely by accident, I happened to create a new set of elements as part of writing an updated user-
guide to achieve very accurate element lengths and to determine what impact (if any) the amount of fold-
back had on the tune.
I cut a random element length, slightly too long for 40m (actually 11.06m) and folded the spare amount of
wire for this long element back down the top section of the DX Commander pole. I considered this would be
too long at the time.
It turns out that I did achieve a perfect tune for 40m,
but this “top loading” meant I also found a perfect match
for 15m band. Actually, the tune ended up at under 21.1 MHz. It also turns out that you can cut this fold-over
shorter and move the 15m up and down as you wish. It now starts behaving similar to a 5/8
th
wave.
Both 40m and 15m are benefiting from this long fold-over but to different effect. 40m is probably hardly
seeing this fold-back since I can cut this back quite a lot and almost nothing happens to the tune.
On 15m, this foldback seems to be a superb accident. And although the 2:1 bandwidth is still over 400 KHz,
it allows the keen operator the ability to tune the element to the portion of the band you want your lowest
SWR (CW, Digital or SSB). Pruning this foldover has negligible effect on the 40m band tuning. One DX
Commander user called this
foldover method a “boomerang” match which seemed to have stuck!
The added benefit is that the physical length of this 15m element becomes close to 5/8
th
wave. I believe this
is why I achieved such a great result on 15m band during the IOTA contest.
ADDING 80m
I successfully changed out the 30m element for a 19.5m long element as an Inverted L on the All-Band-
Vertical Classic in 2017. I
’ve not tried on this Expedition pole. But I see no reason why it wouldn’t work. On
my own Classic antenna, it tuned very well from 3.65 through 3.8, under 1.5:1 SWR for the IOTA contest.
The vertical component was originally around 6.7m high
– however on the Expedition pole, I suggest you
start your
“inversion” at the 5m Upper-Spreader point. Start with 19.5m of wire here. Note, you will get a lot of
bend on the pole in this configuration. It might not look pretty, it
’ll still work :)
GLUE LINED SHRINK WRAP
Find some lengths of this in your kit. You only need a small amount per element to make loops at the top of
each element so that the carabiner can to clip to it. Only fit once elements are correct (start with electrical
tape) because once fitted, they are a nightmare to get off. Further, remember to only fit the lower carabiner
to your shock-cord once your element lengths are confirmed. Until then, make your paracord a little longer
and just tie a loop (carabiners are difficult to remove too!). Alternatives to a genuine hot-air gun are:
plumbers blow torch, low gas flame on kitchen hob, steam from a kettle or a lighter (watch for carbon
deposits).
HOSE CLAMPS
You will certainly need 2 x hose clamps. One keeps your radiating plate from creeping up the pole, one
between the driven plate and the guy plate and also one just under the guy plate. I have found this pole very
“sticky” so for true /P operations, I wouldn’t bother trying to make up a ton of hose-clamps. If your system is
destined to be installed for more than a day, I found self-amalgamating tape to be perfect in securing the
joints, although a pain to remove!
REPEATABILLITY
In practice, I have discovered that you will need to extend the tube out the same amount as you did when
you built the antenna in the first place. This makes sure that the distance between the bottom of the element
and the upper-spreader remains constant. Otherwise, you may find that the shock cord can either be over-
stretched
– or not enough. A firm twist and pull will be required to friction fit.
RADIALS
The wire in your starter kit will give you around 80m of spare wire after you have built your elements. Use
this to build at least 20 x 3.5m radials in 5 bunches of 4 radials. Effectively, this is almost 2-wavelengths of
radials at 40m band and 4-wavelengths for 20m band. Plenty. For 80m, I used very light-weight
“equipment
wire
” for the element.
To give you more confidence, you may also enjoy my video here:
