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40 Thru 10 Meter
 RANDOM WIRE VERTICAL


This simple 40 thru 10 meter wire vertical should enable you to get on all the "New" HF bands
(40, 15, and 10meters) using your new Technician class privileges.
It is adapted from an idea by NF0R, David Gauding, entitled;
"THE PORTABLE RANDOM WIRE VERTICAL"
by
David F. Gauding, NF0R

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......
here is where he uses standard RG58 or RG59 coax to feed the antenna at it's base with a difference.....the end of the coax shield at the antenna is not connected!

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.

Building it!


Note in drawing above that center conductor of coax attaches
to vertical radiator and there is NO connection to the shield of coax.
(The tuner is actually in the shack, not outside)


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:
234 / Freqmhz = length in feet:

Using 7.1mhz plugged into the formula:

234/7.1mhz = 32.957 feet (round to 33 feet)

Use #12 or #14 wire for strength of the vertical length of 33 feet and note that the exact length is not critical. A few inches either way should not matter.

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.

Now all you have to do is get it up in the air in a vertical position supported and insulated on the top end using any construction method needed to support it. It's not 100% critical that it is in the vertical position just do the best you can. (The tuner will "take up the slack").

If you have trees, buildings or other supports handy within reach of your station, just string a support rope between them and attach the antenna in the center...pull it up to the length of the antenna leaving a bit of slack if you want. See drawing above.

The length of coax to the tuner from the bottom end of it is not critical acording to the article, so use only enough coax to run to your tuner and just lay the coax down into the grass at ground level and let it grow over it. It is probably not wise to bury the coax as this may upset the counterpoise characteristics but is certainly worth the effort to experiment with. The feedline can also be supported up above the ground several inches without any major effect on the performance.

Tune up!

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 transceiver!
Set all the controls on your tuner for maximum noise in the receiver by alternately adjusting each control. They will interact with each other.
At some point using the tuner controls, you will no longer be able to increase the noise in the receiver. This is very close to the point where the tuner has done it's "job" in the matching process.

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 power.
If you need help or are not sure of yourself using a tuner....get another ham who has experience with tuners to help you!

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.

Editor's notes:

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.
An alternate method would be to use 3 or 4 radials the length of the vertical attached to the shield of the coax at the end at the antenna location and then feed to the tuner. Or you can always us an alternate antenna type. Have fun with your new HF privileges and experiment with antennas! 73

Give us your feedback about your experience with it! Email us.







  


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