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Tech237
Moderator
Username: Tech237
Post Number: 515
Registered: 4-2004
| | Posted on Saturday, September 02, 2006 - 5:43 pm: | 
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A Practical
Long Wire Antenna for
CB ~ 11 Meter Use.
An Article Written
By
Tech237 ~ Simon
The most practical and simple to make Long Wire Antenna is the resonant variety. A resonant long wire only requires that the length of the wire is approximately resonant at the frequency of operation.
For CB this means the wire must be a multiple of 11.1m or 36ft 6.5 inches. Therefore, a three wave long wire would be 33.3 m (109 ft 9 inches) and four-wave long wire would be 44.4m or 146ft 3 inches in length.
The best wire to use in making a long wire antenna is a hard drawn copper or copper clad wire of around 12 or 14 gauge. These two wires will produce minimum stretch over long periods. The run for the antenna should be as straight and as high as possible, but some slight bending or change in height will not matter too much.
Now a long wire antenna cannot be attached directly to any modern CB without damaging the CB, so some form of coupling device is needed, along with an SWR meter. A simple coupling unit can consist of an inductor (coil) and a capacitor, as shown in the following diagram. For legal power (or close to) the capacitor can be one taken from an old tube receiver, but for higher powers a large unit capable of handling that power level will be needed. However the actual capacitance will need to be fairly close to that specified in the diagram.
Coil L1 consists of around 5 turns of 14 or 16 gauge tinned copper wire, wound around a broom handle. The inner conductor of a short length of coax is soldered to one end of the coil.
The opposite end of the coil connects to the end of your long wire – preferably by using some form of terminal such as those used on power supplies.
Solder the braid of the coax to the frame side of the tuning capacitor. If you solder the braid to the revolving part of the capacitor, you will create a short across the output of your CB and damage the finals the first time you transmit. Solder the other connection of the capacitor to the end of the coil where your long wire antenna will attach.
Initially the tapping connector, shown in the diagram, will be a short length of wire (a piece of braid works well) with an alligator clip at the free end. This is used to experimentally find the correct place for the tap to be connected. By the way, the original version was made in a large plastic box that was weatherproof. To prevent any problems that could occur due to movement, make sure that all the wiring is as rigid as possible.
No connect the antenna, coupler, SWR meter and radio so that you have CB> SWR Meter> Coupler> Antenna, making sure that where the wire comes into the shack it cannot make contact with any metal and that YOU cannot make contact with it.
As an aside, you can mount the coupler outside the shack and use a motor to tweak the capacitor once you have the right location for the tap.
Adjust the tuning capacitor so that the plates are about half meshed and connect the tap near the middle of the coil. Using AM check the VSWR and if the reading is high move the tap to an adjacent turn. Try nearer the antenna first and if that makes no difference or even makes it worse move the tap nearer the radio. Once you have found the best spot (minimum SWR), you can now adjust the capacitor to try and bring it even lower. By the way you may also try adjusting the tap around the turn you have it on in an effort to reduce the VSWR too. You may not ever get a 1:1 reading but in most cases the reading should be 1.3:1 or better, and any reading of 1.8 or less is acceptable. Once you have the lowest SWR you may solder the tap to the correct spot and close the box up. Recheck your VSWR and adjust the capacitor to compensate for any change closing the box created.
Try this antenna and you may just find it out performs that megabuck commercial antenna you have been using.
Respectfully Submitted,
Simon
Tech237 |
Bob_gipson
New member
Username: Bob_gipson
Post Number: 3
Registered: 8-2006
| | Posted on Sunday, January 28, 2007 - 8:13 pm: |
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Simon,
Just had a few questions reguarding the long wire antenna. You said that a 4 wavelength antenna would be 44.4 meters. Is that total or is that each leg of the dipole. If I'm reading it right each leg would consist of a wire 22.2 meters. I was also wondering if anyone had tried to run an antenna turer . I run a Kenwood TS-440SAT and was wondering if it would tune up. I've been wanting a horizontally polarized dx antenna and this sounds like it would make gain and suite my need.
Thanks,
American Kangaroo 511
Columbus Indiana
Personal Bob |
Bruce
Senior Member
Username: Bruce
Post Number: 4340
Registered: 9-2003
| | Posted on Monday, January 29, 2007 - 6:45 pm: |
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G5RV ..... |
Tech237
Moderator
Username: Tech237
Post Number: 804
Registered: 4-2004
| | Posted on Friday, June 08, 2007 - 9:33 am: |
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To answer Bobs, questions let's take annother look at the described antenna.
"You said that a 4 wavelength antenna would be 44.4 meters. Is that total or is that each leg of the dipole. If I'm reading it right each leg would consist of a wire 22.2 meters."
Firstly the antenna is a longwire antenna, which means all the wire is stretched out in one direction from the feed point. This in turn means that the antenna is fed at the end closest, or even inside the shack. So all 44m or wire is in one continuous piece.
" I was also wondering if anyone had tried to run an antenna turer . I run a Kenwood TS-440SAT and was wondering if it would tune up. "
Just about any piece of wqire will tune up using a tuner BUT may not be the most effective of antennas. For a longwire antenna to work effectively it needs to be at or near a natural resonance and not one produced by the use of a tuner. Don't forget that the tuner would replace the matching network shown in the original diagram otherwise that network will cause you all sorts of problems when it comes to tuning the antenna.
" I've been wanting a horizontally polarized dx antenna and this sounds like it would make gain and suite my need"
For a multiband HF DX antenna try either the G5RV as suggested by Bruce (my old one even worked up on 6m) or a fullwave 80m fed into your tuner. Both will work better on other bands better than a longwire antenna cut for one band.
Simon
Tech237
KD7IEB
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