40 Thru 10 Meter
David's original design included the use of graduated tubing sizes for easy storage while transporting it for QRP operations in the field and it required guy wires.
We have taken his ideas one or two steps "backward" by presenting a "modified" design here for fixed (permanent) station use as suggested in his article by using wire instead of tubing.
This antenna was designed to cover 40 meters thru 10 meters.
It is nothing more
than a 1/4 wave length (at lowest frequency of operation) wire going
straight up from an insulator attached to the ground, suspended from above
and fed using a transmatch (tuner) feed to the unbalanced output of
the tuner, but......
It is allowed to
"float" and ungrounded at the antenna, unattached to anything, to act
as a sort of "tunable" counterpoise for the antenna apparently acting as
an RF ground using modest power levels.
Since the antenna is
cut for 1/4 wave length at 40 meters on the lowest band of operation, you
start by using the formula:
Using 7.1mhz plugged into the formula:
234/7.1mhz = 32.957
feet (round to 33 feet)
One end of the wire is
attached (soldered) to the end of your coax center conductor only and sealed to keep out water
making sure the shield is not shorted to it. The shield is not connected except on the opposite end of
the feedline at the tuner. The antenna feed point is attached to an
insulator isolating it from the ground. A simple wooden stake, pvc pipe,
etc can be driven into the ground to provide an insulator and attachment
point at the base. The attachment point at the coax should not be
"grounded" in any way. You mounting (insulating) from the ground method
will depend on what you use.
After you have
installed the antenna and it is supported properly and connected to
the tuner output, turn on the receiver on the CW portion of 40
meters. Make sure your tuner is in line and connected to your
Now using only enough
AM or CW output from your transmitter, (assuming you have an unused
frequency), to get a calibration level on your SWR meter, transmit a short
carrier and look at the SWR quickly and then fine tune the controls on the
tuner for lowest SWR. This may take a bit of practice if it is your first
time. Here again, you will reach a point where you can no longer get a
lower SWR than what you see. Stop transmitting and ID! Transmit only long
enough to adjust the SWR to it's lowest reading. If you get a high SWR and
nothing seems to get it down with the tuner adjustments...Stop transmitting and check EVERYTHING. You may find
in your excitement to "get on the air" that you forgot to tighten a
connector or have a poor solder joint at the antenna or on the jumpers
between the transmitter/SWR meter may be the culprit. Don't damage
the tuner or your transceiver. Try again remembering to use very low
If everything is successful, make a note of the tuner settings where you got the lowest SWR for this band, 40 meters, at the frequency of your transmitter for later use. Keep it for reference.
Now do the same procedure for 15, and 10 meters and remember to make a note of the tuner and frequency settings for each band. You can then quickly change the settings for each band of operation, retune quickly using the reference points and get on the air faster. These reference readings also are very useful to monitor so you can note any changes in the antenna "system" before major trouble.
If you are a Tech class ham you are authorized a 200khz portion of 10 meters from 28.300 to 28.500mhz, for voice (SSB) operation, it is advisable to set your tuner's lowest SWR reading to the center of this portion, 28.400. Just remember to always check your SWR using lowest power before attempting to operate on any frequency of your "New" bands using the tuner. You can check the "center" , upper and lower frequencies of the voice portion to see if the SWR is over 2:1 to 1. If it is, then just use the tuner to find the best settings for each end and the center and mark them down in your notes.
Although this antenna design is like most antennas...not perfect ...and is a compromise antenna.....it will enable you to make contacts. It was originally designed for QRP....low power....5 watts or less...and under adverse conditions, so if you use the stock power level of most HF radios...100 watts....you should have lots of fun. Just remember to use only enough power to establish and maintain communications!
If you don't have the
vertical space to build the 40 - 10 meter version of this antenna, then
just simply utilize the space you have and let the tuner do the "work". If
you can't "tune" the swr lower than about 2:1 then it is not advisable to
use this antenna. Most Hf rigs will start to shut down at 2:1 or higher.
This design can be difficult to tune at some locations.
Give us your feedback about your experience with it! Email us.