SteppIR Antennas 40m - 30m Dipole Kit
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40m - 30m Dipole Overview
The 40m - 30m dipole is simply a driven element that functions as a dipole from 6.8 MHz to
13.8 MHz and as the driven element for the yagi array from 13.8 MHz to 54 MHz. It has no
effect on the performance of the yagi. The yagi works the same with or without this option.
A dipole for 40m would normally be about 64 feet long but we have shortened it to 39 feet
by looping the element tip back towards the boom. This is a form of linear loading and is
very efficient, however, nothing comes for free and with this dipole you lose about .37 db on
40m over a full size dipole. This is hardly measurable at the receiving station end so it is a
very reasonable trade off. On 30m since the copper tape barely turns the corner back toward
the boom it essentially performs like a full sized dipole.
On 40m folding the element back nearly double (the tape comes within about 3.5 feet of the
boom on each side) very conveniently makes the impedance 25 ohms, a 1.0:1 match for our
yagi Balun/Unun. On the 30m, however, we have a full sized dipole whose impedance is
very much dependant on the height above ground so there is a varying degree of mismatch.
Below 40 feet or so you will find the SWR as high as 2.6:1 but at greater heights it can drop
to as low as 1.6:1 SWR.
This small amount of mismatch can easily be handled by the internal tuners on most trans-
ceivers. At 10 MHz SWR values in this range result in insignificant loss, so the antenna will
perform very well on 30m. You will find that on 40m even at heights below 40 feet you will
get a very good match with this type of shortened dipole. If the SWR seems to be too high
try adjusting the driven element length using the “Create Modify” function.
Note: By using the “Create Modify” function to fully extend either the reflector or director 1
on 30m you can create a very short director for the dipole resulting in .5 db gain and
lowering the SWR by about .2. You can then save it and it will be permanent. You
could also save it in both directions (180° and normal), lengthen the reflector in the
180° and the director 1 in the normal direction and now have it reversible. If SWR is
the biggest concern try
lengthening both the re-
flector and director 1 to
get the lowest SWR.
Warm Regards,
Mike Mertel
Michael (Mike) Mertel - K7IR
President
First Prototype Sweep