Sunday, May 26, 2013

Low cost fishing pole vertical antennas

Low cost fishing pole vertical antennas 


Introduction
These antenna ideas are aimed at those who have limited space for antennas and want to make their own antenna using ordinary household tools, using parts that are easily obtained, and needing little in the way of test equipment.

The performance of these antennas can be every bit as good as a multi-band commercial vertical and at a fraction of the cost. In the case of the parallel wire version (without traps) the performance can exceed the commercial units.

These antennas are based on a 10 metre fibreglass fishing pole. It is important to use fibreglass poles, not carbon fibre. Fishing poles can be obtained from several sources, including eBay. They are also sold as flag poles of the type used to fly banners at camp sites. The more expensive "Spider Poles" can be used, however ordinary low cost poles are quite adequate.

Band Options
A ground mounted vertical will be less efficient than one mounted on a pole used with elevated radials. However, most of us will not want to clutter a small garden with radials at head height, so often opt to mount a vertical antenna at ground level. On 7 and 10 MHz the performance of a ground mounted vertical is good compared to a typical dipole at 10 Metres above ground and will generally out perform the dipole for DX, however on the higher frequency bands the performance compared to the above dipole drops off but may still work well when conditions are good.

Vertical antennas can also be made for use on 80m and 160m, however for better efficiency (and ease of adjustment) these are generally better used in an "inverted L" configuration with a horizontal top wire. A modest sized 160m vertical, as described below, will enable signal exchanges of 5 x 9 to be made with European stations from the UK on most evenings when running 100W or less.

There are several "easy" combinations which work well together for multi-band home made verticals, the examples shown here are a trap vertical for 7 and 10 MHz, a trap vertical for 7, 10, 18 and 24 MHz and a parallel wire vertical for 7, 10 and 14 MHz. Variations are of course possible, such as a parallel wire for 14 MHz added to the trap vertical. The four band vertical uses two parallel wires with a single trap in each wire, one trap is tuned for 10.1 MHz and the other for 24.9 MHz. Some bands are quite close in frequency and will limit the choice of frequencies used in an antenna, for example 24.9 MHz can clash with the 21 and 28 MHz bands. One possibility would be to use two antennas, one for 14/21/28 MHz and the other for the WARC bands of 10/18/24 MHz.

A 3 band elevated ground plane for 14/21/28 MHz can be easily made using a 21 MHz trap in a 14/21 wire with a parallel wire stood off by around 7 inches on fibreglass tubes for 28 MHz. I use this antenna for my station in Spain with the wires taped to a 7 metre fishing pole mounted on a roof balcony, with two radials per band. The fibreglass tubes are 6mm diameter and fixed with epoxy adhesive into 3 hole "modesty" plastic blocks of the type used to secure wooden panels, in turn these are securely fixed to the pole with Ty-raps.

Multiple traps can be used in a single wire with the vertical, however the performance will drop with every trap that is added. By limiting the number of traps to no more than one per wire, the performance is maximised.

Capacitors can be re-used and traps are easy and cheap to make, so feel free to experiment!

Materials, tools and test gear
The following items are needed depending on which version you make:
Fibreglass pole, wire (suggest 32/0.2 wire), roll of black PVC tape, 6 or 8mm fibreglass tube (or PVC 16mm oval electrical conduit and 12mm dowel), 40mm plastic waste pipe, 14 SWG (2.0mm), or 16 SWG (1.5mm) enamelled copper wire for trap construction or slightly thinner for loading coils, 25 pF 7.5 KV "door knob" capacitor, polypropylene garden twine or thin rope, fence post, guy stakes and cable ties.

14 SWG (2mm) wire is the largest practical diameter for winding coils on 40mm plastic tube, however the thinnest should not be much less than 16 SWG to keep trap loss to a minimum.

In addition to hand tools and a soldering iron, the following are also needed:
Hot melt glue gun (traps), dip oscillator (traps) and an antenna analyser or SWR bridge. Optionally, a low cost capacitance and inductance meter can be useful for checking capacitors and loading coils... The LC200A type of meter is easier to use for LC measurements than an antenna analyser.

You may also opt to make a feedline choke in a suitable box, the additional items needed are a coax socket (SO239), two terminal posts, ferrite ring (suggest FT240-31 or FT240-43 for higher bands, FT240-73 for 160m) and a short piece of RG58 coax (or the more expensive Teflon coax, RG142, for power levels up to 1.5 KW).

Door knob capacitors, fibreglass tubes, enamelled copper wire and ferrite rings can be obtained from eBay suppliers. Conduit and waste pipe came from local DIY stores. Spiderbeam supply 1 metre lengths of RG142.

Parallel wire vertical
To minimise interaction between the wires in a parallel wire vertical it is necessary to space the wires well apart. To allow for the pole flexing in the wind, at least 300mm spacing is suggested. Spacers can be made from 16mm wide oval electrical conduit or small diameter fibreglass tubing - 6mm or 8mm diameter is strong enough. By itself plastic conduit is quite weak, to strengthen the point where the spacers are fixed to the pole it is necessary to add wooden dowels. These only need to be around 120 mm in length by 12 mm or so in diameter, and can either be used to join two lengths of conduit "back to back" or pushed into the conduit from one end. I used 480mm lengths of conduit joined "back to back" plus the single 480mm length for a top support. To lessen the visual impact of the antenna, I covered the white conduit with ordinary black PVC insulating tape. The spacers are fixed to the pole with a pair of cable ties.

The wire lengths are calculated from the formula L = 234/F, where F is the frequency in MHz and L is the wire length in feet. These lengths work out to around 33' 3", 23' 2" and 16' 7" for the 7, 10 and 14 MHz bands. The lengths are generally shorter in practice than the formula suggests which is just as well as otherwise the pole wouldn't be long enough! However probably due to interaction between the wires, the 14 MHz wire needed to be around 4" longer than calculated. Wire size is not critical, but it is probably better to avoid the thinnest "hookup" wire, I use 32/0.2 wire. Note, ground conductivity/loss and elevated/buried radials make a significant impact on both the performance and tuning of a ground mounted vertical.

Start with a single wire for the lowest band (longest wire), tape it to the fishing pole in a spiral fashion, ensuring each joint in the pole is taped to avoid it collapsing, then fold the end of the wire for minimum SWR, add the next band up and trim/fold, finally add the highest band and trim/fold. There will be some interaction, so it is better to fold the ends rather than cut and have to add an extra length of wire.

Trapped vertical
Instead of using parallel wires, home made traps can be used. Commercial trapped antennas are very popular, can be expensive and often perform poorly. While traps appear to offer the advantage of multi-band operation on a single vertical pole, the disadvantage is they shorten the antenna, which in turn lowers the feed impedance and reduces the bandwidth. There will also be some loss associated with each trap, however it should be less than 1 dB. The overall height of the 7 and 10 MHz trap vertical shown here is approx 26 feet, the top two sections of the fishing pole are not used (the open tip is taped to keep rain out).

Trap construction
The 7 and 10 MHz dual band trap vertical needs a 10.1 MHz trap. The trap shown below comprises 18 turns of 16 SWG enamelled copper wire wound on a 40mm diameter plastic pipe offcut which had been wound with black PVC tape to minimise the visual impact. A 25 pF 7.5 KV "door knob" capacitor is placed inside the coil and soldered in parallel with it. Start with 20 turns of wire and remove a turn at a time until the trap resonates at 10.1 MHz using a grid dip oscillator. Stretch or squeeze the coil until the dip oscillator shows a resonance in mid band, this is with the coil and capacitor on their own, i.e. without wires attached to the ends. Check the calibration of the dip oscillator against a receiver, when you are satisfied the trap is set where you want it, secure the coil with hot melt glue. A plastic disc was glued on the top of the trap to keep rain out. The exact value of the capacitor is not critical, as the capacitors are mostly surplus the choice can be limited to the value you can source. 50pF capacitors with fewer turns on the coil could be used. Avoid wire ended capacitors, even if they have the Voltage rating, as they will not handle the current. The type of capacitor I used is shown below.

If you want to make a 24.9 MHz trap, try 7 turns of 14 SWG on a 40mm former with a 25 pF capacitor. The trap shown below right, has been secured to a PVC stand-off arm with hot melt glue - which adheres well to this type of plastic.

Note: Various articles mention the need to avoid a trap being resonant on the band you are using it for. This is quoted as being necessary to reduce losses and to reduce the peak Voltage across the trap. When a trap is tuned "on it's own" the resonant frequency will be reduced when used in an antenna, for example the resonant frequency of a trap tuned for 24.9 MHz was reduced to 21.5 MHz in this antenna.

While it is possible to use traps made from coaxial cable, coil and capacitor traps have less loss and greater power handling. A previous trap made from RG58 coax exhibited SWR creep at power levels between 200 and 300 Watts.

There is no need for additional weather coating on the traps, rain doesn't alter the performance as far as my SWR indication shows.

Power handling
The above traps have been tested at the UK limit of 400 Watts with no sign of SWR change or any other unwanted issue. Traps made from 7.5 KV "door knob" capacitors should be good for 1 KW output and probably more. Higher Voltage capacitors are available, but tend to be large and heavy.

Wire cutting and antenna tuning (trap vertical)
Unlike the parallel wire vertical, with the trap vertical start with the highest band (shortest wire) and fold/ trim the wire for optimum match, then solder the trap onto the wire and add 5 or 6 foot of wire at the tip. Check the higher band still has a good match, then fold/trim the wire from the tip for the lower band.

If you want to try a dual wire, dual trap antenna, for 24/18 MHz (one wire) and 10/7 MHz (the other wire) the order of assembly is as follows:

Cut/trim the 10 MHz wire, add the 10 MHz trap, then add the tip wire and trim for 7 MHz. Then add and trim a parallel wire for 24.9 MHz, finally add the 24.9 MHz trap and trim the associated tip wire for 18 MHz. This combination works quite well, although my minimum SWR on 18 MHz is around 1.7:1.

Verticals for 80m and 160m
Loaded verticals for 160m and 80m have been popular for a number of years and are easily made. In order to give maximum efficiency the loading coil is usually mounted near the top of a vertical pole with a horizontal wire running from the coil. Several combinations of vertical and horizontal wires are possible, examples for 160m include a 25 foot vertical wire, 64 uH coil and 45 foot of horizontal wire or a 132 uH coil and 25 foot horizontal wire. While it makes calculating the length of wires difficult, using 3 or 4 wires in the form of "spokes" from the top of the coil will improve performance over a single wire. A 40 foot vertical with 4 x 50 foot wires from the top of the vertical will resonate on 160m without needing a loading coil, however that spread of wire is not practical in many modern garden sized plots.

As the bandwidth of loaded antennas is very narrow, especially one for 160m, any change to the value to the value of the coil or movement of the pole will impact on the resonant point. Try to use as large a diameter of enamelled copper wire in the coil as practical (to minimise heating) and also try to keep the antenna away from other antennas and metalwork.

Similar arrangements to the suggested dimensions for 160m can also be calculated for 80m, although a full quarter wave "L" (without needing a loading coil) is not too large to install in many gardens. Tip... use a long enough horizontal wire to allow it to be lowered to within your reach by using a cord and pulley, it is much easier than lowering the fishing pole each time you want to move to a different part of the band.

Calculating the dimensions for 80/160m
There are several "on line" calculators for short wire antenna dimensions and loading coils, one example being the University of Edinburgh one. On the page there is a link to a coil winding calculator too. I have an inductance meter which is handy for checking coils, but for all practical purposes a loading coil need not be an exact value as the antenna will be tuned by adjusting the top wire.

Matching a 160m (or 80m) loaded vertical
Unlike the case of the higher frequency verticals, where the feed impedance is usually not far removed from 50 Ohms and a reasonable match easily obtained, when you use a loaded vertical for 160m the feed impedance should be much lower than 50 Ohms, how much lower depends on how many radials are used. In my case, with less than ideal radials, the feed impedance of a 25 foot + 25 foot "inverted L" 160m antenna was 21 Ohms.

In order to match the 21 Ohm feed to 50 Ohm coax a choke of approximately 3 uH was added across the feed point (lower end of the vertical wire to the radial connection point). The method of tuning is fairly straightforward if you use an antenna analyser. The 3 uH choke was made by wrapping 7 turns of 2mm enamelled copper wire around an aerosol can to form an open coil of roughly 80mm diameter that could be compressed/tuned with Ty-raps (the can is not used as a coil former only as a means of winding an air cored coil...), the value varied between approximately 1.5 uH and 4 uH depending on how compressed the coil was. There is an image of the coil lower down the page. For 80m a matching coil of half that size should suffice.

To adjust the matching coil, firstly you will need to adjust the top section of the loaded antenna without the matching coil in place. Connect the antenna analyser directly at the feed point, using as short a coax cable as possible, then adjust the antenna top wire until the reactance (X) is as near zero as you can manage at the frequency you want the antenna to operate on. Note X = 0 is the resonant point, which may not be where minimum SWR occurs. At this stage the SWR will be quite high, around 2.5:1 being typical. The resistive component (R) displayed on the analyser will probably be around 20.

Leaving the analyser set to the resonant frequency add the coil across the feed point and squeeze the coil until the resistive component equals 50, the SWR should drop significantly as you reach R=50. Tighten the Ty-raps to secure the coil at that matching point.

Note, the bandwidth of a short vertical on 160m will be very narrow, as narrow as +/- 10 KHz for a 2:1 SWR is likely with a 25 foot plus 25 foot antenna.

Mounting
The pole is fixed to a square section wooden post with re-usable cable ties (Ty-Raps) and will self support. Beware that most of the DIY grade cable ties may not be strong enough to use for this purpose. For windy locations guy lines can be added. These need not be elaborate, polypropylene garden twine secured to plastic tent pegs is good enough in all but the strongest of wind. Check the guy lines are strong enough, some plastic garden twine is so weak it can be easily broken by hand.

Radials
Like all ground mounted quarter wave verticals this one needs radials, the more the better. I currently have 16 random length radials cut into the lawn which return to an earth rod set into an old plant pot. The pot has a sandstone paving slab covering it. Buried radials can use any low cost wire, some of the less popular colours can sometimes be obtained at bargain prices. My radials use PVC insulated 32/0.2 wire soldered to a wire ring made from the same wire. The insulation isn't of course needed for buried radials. Buried radials do not need to be a 1/4 wavelength long as the soil de-tunes them, radials two thirds of the length of an elevated radial are optimum when buried 2 or 3 inches down in soil (22 feet as opposed to 33 feet on 7 MHz), however if you can't install radials of that length, put as many down as you can manage at whatever length fits.

Feedline
The antenna is fed with RG213 coax via a plastic junction box. The junction box includes a ferrite ring choke to minimise currents on the outer braid of the coax. The choke is made using 8 turns of RG58 (or RG142 for QRO) coax on an FT240-43 ferrite ring (or FT240-73 for the lower bands).

Frequently asked questions - Click here, opens in a new window

Results
The parallel wire vertical has a good SWR on all three bands with a minimum around 1.2:1. The dual band trapped vertical has a minimum SWR of approx 1.3:1 rising to 1.6:1 at the band edges. The four band (two parallel wires, one trap in each) gives similar results except the 18 MHz band has a minimum SWR around 1.7:1, the 160m antenna gives a perfect match at resonance, but is very narrow bandwidth.

On air results are much as you would expect from a ground mounted vertical. On 7 MHz the vertical is generally 2 or 3 S-units better than a dipole with it's apex at 30 feet for DX stations and often stronger into Europe as well. On 10 MHz the difference is less but the above generally applies. On 14 MHz the antenna is worse by 2 or 3 S-units on many EU signals however DX is usually better with the vertical. A 25ft vertical with 25ft horizontal wire and 132 uH loading coil gives S9 signals across Europe after dark while running up to 100 Watts.

DX worked in March 2006, running 60 Watts of CW, include:

7 MHz 4X4, 3B8, 5R8, 5H1, 9M2, 9M6, FS, A45, VR2, VY2, VK, ZL, BV4, J88 and SU 
10 MHz 6W6, XU7, P40 and ZF2 
Parallel wire vertical

10 MHz trap in 7/10 MHz vertical

24.9 MHz trap in 24/18 MHz parallel wire

160m loading coil



10 MHz trap using 16 SWG wire
"Door knob" capacitor

Feed arrangement showing 160m matching coil (remove the coil for use on 40m and higher bands)

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Multiband wire vertical


Multiband wire vertical


The first antenna everybody probably makes is a dipole and the second a quarter wave vertical. The third antenna will probably be a multiband version of these antennas (or yagi). This is the third antenna..

Below a small description of an easy to make and cheap multiband wire vertical. The antenna has like the fan dipole parallel wires for the bands for the bands it has to work on. All antenna wires are all attached to one side of the balun and attached to the center pin of the coax cable. All radials are all attached together to the other side of the balun and attached to the shield of the coax cable. Some distance is needed between the wires to make the antenna easy to adjust.See the picture of the first version for 10, 15 and 20 meters.

The antenna is:

Easy to make
Cheap
No traps
Light in weight
An easy antenna project
Great for field day use and as ‘extra’ antenna at home for additional bands (or contests).

Needed materials are:

Fishing rod (of better) with length equal to lowest band ¼ wavelength
Bread cutting board (broodplank) (from Hema, IKEA etc.)
Some 5/8 or ¾ inch electricity plastic
Some tyraps
Feed point with 1:1 balun
Some cheap wire as antenna and radial wire
Some gear for cutting and drilling

The pictures give an idea how I made the first example. It took me about 2 hours to make it.

Mast and wire support
There are several supports used for the wires on the sides of the mast. The center wire for the lowest band is attached alongside to the center mast. The other wires are supported using PVC electricity tubing. I like the gray ‘heavy duty’ tubing.

The PVC tubes are attached with tyraps to a strip of plastic cut from a bread cutting board. This board is again attached with tyraps to the mast. See the pictures below.

The distance from the center mast to the end of the side wires is 25 cm (10 inch). Not very critical but it was the total amount of tubing I had available which gave me this length. Don’t make the distance to the center mast very short (like 5 to 10 cm). Of course this can be done (like the Cushcraft R8 or Hy-Gain AV-620 / AV-640) but will make adjusting the lengths very critical.

When 3 bands are used a center pole and 2 wires on the sides are used. The center wire will always be the lowest band and to the sides the other two or four bands. When 5 bands in total are used the 4 wires will be around the center wire each on 90 degrees. When more than 3 bands are used the 2nd and 3rdband are on the same spreaders and also the last two bands to use a minimum of spreaders.

In the spreader tubes holes are drilled to pass the wires through. The wire will only be fixed on the bottom spreader tube and the top spreader tube. The wire is allowed to slip through the holes of all additional support spreaders in between. To not have slipping the wires through the holes in the spreader tubes I bent the wires a bit. See pictures below. A probably better way is to use a kind of thickening of the wire (using a luster or screw terminal over the wire). The top spreader tube will be about 10 cm under the end of the wire. The top of the wire can be fixed the same way on the top spreader as on the bottom spreader. When the center tube is very flexible it is probably wise to use some king of flexible material so the wires can slide through the holes in the spreader tubes and only fixed to the spreaders at one point. In this case the wire should have a flexible connection to the top or bottom spreader tube and fixed to the other top or bottom spreader tube.

Front side

Back
side


As PVC is used no additional insulators are needed with low to medium power. The top of the wires will have the highest voltage and might need better insulation with high power.

Feed point and Balun
This was the first test and no balun was available… Of course the antenna needs a real 1:1 balun/choke to isolate the antenna from the coax cable. The antenna wires going up are all attached to one side of the balun which has to be the middle pin of the coax cable. All radials are attached together to the other side of the balun and attached to the shield of the coax cable.

The balun used is of the type W1JR using RG303 Teflon coax on a RK4 ferrite core bought from the DARC Verlag. This ferrite core is cheap and has good specs. Below two versions of the baluns I use.



First try feed point.. 


Balun with connectors on the sides. 


Balun with N-connector in and out.


Wire length
The length of the wires can be easily calculated using the formula for a quarter wave dipole which is 75 / frequency. Most ften we can take of 5 percent making the formaula (75 * .95) / frequency = 71.25/freq (per side of the antenna. Starting a bit longer will never hurt. Always start with the longest wire (lowest frequency) and then go back (from lowest frequency to the highest frequency). The wires are closely spaced and will interact. So some tweaking is needed to get it working for all bands. The wire I use is 0.8 mm aluminum wire without insulation (cheap buy).

The mast length used has to be at least half to one meter longer than the longest wire length as a minimum but longer is always OK.

Radials
The radials have (about) the same length of the radiator wire for that band. Each band uses one radial (as a minimum). The easiest is to place the mast on a pole and slope the radials to all sides to ground poles/pins (of course isolated to ground). Also the radials need one or two spreaders.

Guying
The mast should not be to flexible. As it bends, the centre mast will not change length much. The wires on the sides sticking out of the centre mast will become longer or shorter when the mast bends. So guy the mast or make it rigid.

Alternative antenna using double height.
An alternative is to double the mast length and also use spreaders for the radials below the feed point. Using this setup the coax cable has to be directed away from the feed point at a 90 degree angle. An extra PVC pipe could be used to have the coax extended out of the mast for 50 cm (or more) and then slope the coax to ground at a 45 degree angle.

Example Antennas




For 20 and 15 meter at 4.95 and 3.28 for the ends of the wires and at 20 cm. For 10 and 6 meter at 2.43 and 1.32 for the ends of the wires and at 20 cm. Plus two radial spreaders.

The 17 and 15 meter wires are using the same spreaders. The 12 and 10 meter spreaders also use the same spreaders.









For 40 and 20 meter at 10.0 and 4.95 for the ends of the wires and at 20 cm. For 15 and 10 meter at 3.28 and 2.43 for the ends of the wires and at 20 cm. Plus two radial spreaders.


The 80 meter wire will be used as inverted L and will extend from the top of the mast at around 11 meters away from the mast for the additional length of the wire. An insulator at the end should be used. As the mast now will probably bend to the direction of the 80 meter wire 1 (or better 2) wires could be used to keep the mast straight. With a length of 11 meters for the mast one or more additional guy wire could be used.

Many more antenna configurations are of course possible.

Below a picture of the antenna on the back of our barn. It’s on a pipe and the radials are spread out over the flat roof.


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C-POLE Calculator


C-POLE Calculator



Most amateur radio operators who are involved in portable operation spend a fair amount of time looking for antenna systems that are light and portable, easy to set up and take down and that demonstrate high performance. Based on the original design (QST Magazine, April 2004, p.37) by Brian Cake, KF2YN, here’s a vertical that’s small, light and portable, needs no counterpoise and performs as well as many home antennas. Visithttp://www.qsl.net/hb9mtn/hb9mtn-c-pole.html to see construction details for this antenna. 

The HB9MTN web site shows an antenna that is designed for use on the 20 meter band, however this can be scaled for use on other bands. This page contains a calculator that will give you the appropriate length of each segment in the drawing. It uses the base reference frequency of 14.24 MHz and directly scales the length of each segment based upon your desired operating frequency. 

To use the following calculator, enter your desired operating frequency in the “Target Frequency” box and click the “Calculate Lengths” button. Then use the resulting calculated lengths with the corresponding lettered segments on the diagram to cut your antenna to the right length. Always check your antenna with a reliable SWR meter to avoid damage to your transceiver. 

Thanks to Brian V. Cake, KF2YN, for the original antenna design, to Ed Bosshard, HB9MTN, for the graphics, photos and construction details, and to Tim McDonough, N9PUZ, for providing the spreadsheet that the calculations are based upon.





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MAGNETIC LOOP FOR 80m - 40m

MAGNETIC LOOP FOR 80m - 40m

EVOLUTION OF A PROJECT ...

December 2002:
Two turn CELLFLEX 1/2"-CABLE-LOOP for 80m - 40m, Diameter 1.6m, 
Spacing 0.1m, Capacitor 150pF max.

June 2003:
Same loop at final place in attic

Detail of coupling loop and experimental capacitor
(theoretically 128 pF/3.2 kV for 80m, 14 pF/5.6 kV for 40m at 50 W)

October 2003:
Planned Hinge-Capacitor, Remote Control via Motor-driven Excenter
(Plates 25x25cm, Spacing at 80m = 625 cm2/128pF = 4.88mm, 
Spacing at 40m = 625cm2/14pF = 44.64mm)

December 2003:
Stepper Motor Remote Control Experimental Hookup
(saia-burgess Unipolar Stepper motor Driver SAMOtronic 101, 4 Series Resistors,
Excenter Disk, attached to Stepper Motor and Worm Drive Gear from dismanteled HP DeskJet-Printer.
Full Step Mode: 2 R/min, Half Step Mode: 1 R/min, adjustable)


S1 = FORWARD/REVERSE, S2 = FAST/SLOW

June 2005:
Remote-controlled 68pF variable Capacitor + parallel 80pF fix
(For 80m only, I dropped the Hinge-Capacitor-Idea and added 40m to my Indoor Multiband Diple!)

Read more...

Saturday, May 25, 2013

MULTIBAND H-POLE


MULTIBAND H-POLE
VERTICAL WIRE ANTENNA FOR 160m - 10m

After several attempts to build a multiband C-Pole I finally ended up with the Multiband H-Pole. C-Poles for different frequencies on one pole must be fed with separate feedlines over separate current baluns.

In a first attempt I fed the H-pole in the center with a ladder line. It was electrically no longer an "off-center-fed-dipole" as the C-Pole was, but a vertical, folded "doublet".

The C-Pole is a resonant antenna, whereas the H-Pole is non resonant and must be matched with a tuner.
Construction and materials used for the H-Pole are similar to the C-Pole. I use non conductive glass fibre fishing rods, beware of conductive carbon fibre!

The first results are very promising. I had contacts with excellent signal reports within a few minutes on all bands except 80m at @ 12:00 UTC in July 2008.
I used the SG-239 Automatic Tuner (asymmetric !). So far, the sound of the automatic tuner, was "healthy", only a few "clicks" and down was the SWR! I connected the lower half of the H-Pole to the ground connector, the upper half to the "hot" side of the tuner output.

Dimensions [metric, in cm] and appearance of center fed H-Pole with ladder line, feedpoint 520cm,
lowest spreader 50cm over ground. [Wires accentuated for better visibility]


Elevation Diagrams H-Pole [black] Versus C-Pole [blue], 0.5m over MININEC-Ground, 20m-Band
The Azimut Diagrams for both antennas are omnidirectional



Elevation Diagrams H-Pole 3.7MHz [blue], 7.06MHz [green], 14.24MHz [black], 21.24MHz [violett], 28.5MHz [light blue],
0.5m over MININEC-Ground



See EZNEC-File: multi-h-pole-tl.ez

Only after Peter (HB9CET) asked: "Why don't you feed at the bottom?" I checked for the best feedpoint around the lower part of the antenna and found an optimum, both electrically and mechanically: the lower horizontal wire (#6 in the EZNEC-File).

Dimensions [metric, in cm] and appearance of 25% / 75% off-center fed H-Pole with ladder line, feedpoint 250cm,
lowest spreader 50cm over ground. [Wires accentuated for better visibility]




Elevation Diagrams off-center fed H-Pole [black] versus center fed H-Pole [blue]
20m Band, 0.5m over MININEC-Ground

Azimut Diagrams off-center fed H-Pole [black] versus center fed H-Pole [blue]
20m Band, 0.5m over MININEC-Ground

See EZNEC-File: multi-h-polecet.ez

So far the EZNEC simulation. Field tests will follow. The anttenna has a slight directivity, the F/B ratio is 0.97dB. 


This final version of the multiband-H-Pole Antenna is no longer a vertical folded doublet, 
but again an off-center-fed-dipole, as the monoband-C-Pole was, with no noticable difference in performance.

Feedpoint at 2.5m over ground

7.5 m homebrew ladder-line, 6 cm spacing, 
spreaders from Nylon sheet material

40cm Isolator from Lawn Trimmer String

Smartuner SG-239 with battery

H-Pole Set, ready to go for portable operation


And finally a report from Antonio, CU8AS: 

Dear Eduard

The Multiband H-Pole Vertical Wire Antenna article was forwarded to me by my good friend Hermann Stein, HB9CRV, who is also my QSL Manager.

That was the used antenna, exclusively, at the Helvetia Contest 2012 a couple of days ago and I am very pleased with its versatility, all 9 bands, (160m to 10m).
On 160m I had a contact with HB9CA, super station!

As for the lack of proper 12m tall pole, it was slight sloped towards true orth. With exception of the 10M Band, the Log shows contacts in all Contest Bands. Power used, sometimes, was 1.2 K from an OM2500 Amplifier.

For the 250cm feeding, I used the 24.5m long 450 Ohm ladder line and a 4:1 HP Balun that I took from a factory Original Cobra antenna that was previously at that 10m tall pole. RG-213 was used from the balun to the shack.

The H-Pole needed very light tuner assistance (Ten-Tec 238C).

As annexed files are a few photos of the H-Pole antenna, in Albarnaz, next to the Light House, of Flores Island, Azores

Thank you for the outstanding design.

Vy 73

Antonio - CU8AS




Many thanks, Antonio, for your report and the pics!

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BUDDIPOLE VERTICAL DIPOLE FOR 40 METERS

BUDDIPOLE VERTICAL DIPOLE FOR 40 METERS

SAME ANTENNA AS BEFORE, BUT WITH BUDDIPOLE PARTS


Vertical dipole with capacities on both ends


Parts list and schematic setup


What a beauty!


Coax should be routed as far away from the antenna as possible
an angle of about 45° is disirable


Rotating guy plate
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A C-Pole Antenna for QRPxpeditions


A C-Pole Antenna for QRPxpeditions

I've finished yet one more version of my Crappie Pole antenna, this one based on KF2YN's ground 


independent vertical antenna (or C-Pole). See here and April 2004 QST, page 37, for more information. After trimming it a little it measures 1:1 at 14.060 MHz rising to 2.5:1 at 14.35MHz and 1.2:1 at 14.0MHz.

I found the choke balun to be key to making this antenna work. With no choke the SWR was over 14:1 at 14.060MHz and with a 10 ferrite bead choke the SWR was still 2.8:1 at 14.060MHz. What I'm using now is 15 turns of RG8X single layer wound on a 4" plastic coffee can.

 

This antenna is about 18' tall, self supporting without guys and has only a 4' x 5' footprint. It breaks down to a bundle 5' long. Physically it looks like a tall skinny goal post. Add a birdie and two racquets and it should fit well into a typical camping weekend.

View a video of me setting up this antenna athttp://www.youtube.com/watch?v=nYn-GnwcSoE



Today I made several nice contacts using my K1 at 5 watts and this antenna including W8CQU in Ohio (599), WA3SLN in Pennsylvania (449), W0WCA in Colorado (449), KI0II in Colorado (549) and N4ESS in Florida (579).

This antenna is going with us when we go camping this summer. Thank you KF2YN.

Update: On June 23 I worked EA6UN on the Balearic Islands off the coast of Spain in the western Mediterranean Sea. That's over 4600 miles on my five watts and this antenna. I found Jurek calling CQ on 14.050 MHz with no responses. He came right back to me and gave a 579 report.


A Two C-Pole Steerable Array

Yesterday I finally got my two C-Pole phased array up and on the air. In fact, after tuning it a little I easily made two QRP contacts, one with N2UGB in NY and the other with CT4RL/1 in Portugal.

My journey from idea to an antenna was based on Chapter 13.3, "A Steerable C-Pole Array" in Brian Cake's book, "Antenna Designer's Notebook". Here Brian presented a design based on phased array theory and modeling. Brian was not aware of anyone that had actually built one.

The C-Poles themselves are made from Radio Shack 18 gauge stranded hookup wire. 1/2" PVC pipe is used for the top and bottom 40" spreaders. For easy supporting, the two C-Poles are in the same plane and aligned with the rope joining the two antennas. The upper inside corners of the antennas are connected by a 33.5' length of rope. This insures correct spacing. Support ropes are tied to the two top outside corners. Instead of a relay I used a coax T connector. L3 was added/removed as needed to change the radiation pattern.

Without L3 the array is endfire and, according to Brian's modeling, good for 1.18dBi gain. By adding L3 into the short/L2 side both sides become 3/4 wavelength long and the array has 3.5 dBi gain broadside.

I learned a little along the way about...

Baluns and phasing lines...The phasing lengths include the phase delay introduced by the required choke baluns. I had planned to use air core baluns consisting of RG-8X wound around 4" plastic coffee "cans". What I found was that each balun takes about 1/4 wavelength (electrically) of coax. By the time I added the baluns to L1 and L2 in the accompanying diagram I couldn't separate the antenna by a physical half wave. I was forced to use more expensive ferrite toroid baluns that require less coax.
Adding/removing L3...The switch/relay proposed by Brian in his design introduced its own challenges. The relay/switch is part of the phasing network. I found that my DPDT toggle switch with the needed connectors introduced more phase delay to the point that I was again in trouble with the physical separation of the two antennas. I eventually used a T connector instead.
Supports...Finding trees with the right separation, orientation, height and limb placement can be a problem...especially for a temporary installation in the park.
Measuring the electrical length of coax...My MFJ Antenna Analyzer gave a broad X=0 reading. My grip dip meter gave a sharp dip but not on the same frequency as the MFJ (The ARRL Antenna Book recommends against using a dip meter). Eventually I averaged the two MFJ endpoint/X=0 readings to get a center/single frequency and then calculated the coax electrical length based on that frequency.
Gain...1 to 3.5 dBi of gain is hard to notice when asking for signal strength comparisons under real band conditions.
This antenna array may be a good alternative for someone with properly located supports but my typical picnic table operating style doesn't always allow that. This was as interesting exercise but I'll probably keep using my single C-Pole when I'm at the park.


More C-Pole Vertical Array

After building/using my two C-Pole array I'm starting to rethink my plan.

KF2YN's C-Pole vertical array design calls for dedicated C-Poles (each pruned to have a 25 ohm input impedance) and phasing lines that both transform the antenna impedance to 100 ohms and set the phase delay between the two antennas. On the surface this looks doable but I've a lot of concern about getting the phasing lines right. W8WWV's measurements showed about a 4% delta as he measured the electrical length of a 17.1' long piece of coax. Also, I don't want to dedicate two C-Poles to an antenna that I won't be using much.

A local friend of mine wants to build a self supporting C-Pole antenna like mine. I can feed two verticals with arbitrary (but equal) lengths of coax and a simple Tee connector at the antenna tuner to make up for the 25 ohm combined feed impedance...no need to worry about electrical lengths. In addition, self supporting antennas can be positioned anywhere to point my signal where I want it to go that day. I can even boost the gain a little (up to 4.8 dB) by separating the antennas 5/8 wavelength.

It's still August, I should have another couple of months of outside weather here in Minnesota.


Phased C-Pole Antennas for some Gain

How many times have we seen 18 wheelers with CB verticals mounted on their mirrors? Doing this, truckers add a little gain on 11 mtrs. With proper spacing this works even better on 20 meters.

Today was a sunny day here in SE MN. The temperature was in the low 70s and there was no sign of rain. It was a great day to meet Rodney, KD0EBT, and Steve, KD0ORM, for a little KX3 time at Rochester's Essex Park. My August 23, 2010 blog post proposing that two C-Poles be fed in phase is based on information in the ARRL Antenna Handbook. Information there states that two verticals fed in phase and spaced 5/8 wavelengths apart exhibit almost 5dB gain over a single vertical. My experiments today seem to confirm this information.

I already have one self supporting 20 mtr C-Pole antenna. I built a second 20 mtr C-Pole. This one hangs from a tree limb like W5USJ 's. A little searching around Essex Pack identified a tree with some open space to the south. I merely hung one C-Pole in that tree and set my self supporting C-Pole about 44' (5/8 wavelength on 14.1 MHz) to the south. This put the two broadside to the east/west. I fed each of the antennas with 50' lengths of LMR-400 low loss coax. At the rig I had a short coax jumper to a tee, connecting my KX3 to both antennas. I let the KX3 internal turner take care of any mismatch caused by driving the two 50 ohm C-Poles in parallel. Measurements using the Reverse Beacon Network showed that these two C-Poles fed in phase and spaced 5/8 wavelength apart really can have 5 dB gain over a single C-Pole.

Now I've another portable antenna option for those days in the park.


A Choke Balun for Phased C-Poles


It is important that the baluns used in a phased verticals match, otherwise the phasing, beam pattern and gain won't be as planned. They also must handle the high common mode potential at the feedpoint. KF2YN shows two different balun designs in his April 2004 article. One is just multiple turns of
coax wound around a piece of PVC pipe while the second uses a ferrite core. The ferrite core design, while more expensive, also has much less power loss. For my phased verticals I chose Brian's toroid design. It 
uses 19 turns of RG-174/U coax wound on a FT-240-67 core. I mounted mine in plastic electrical boxes with an eye-bolt to allow hanging from the bottom C-Pole 40" spacer. This balun does no impedance transformation. The balun coax is simply in series with the antenna feedline.

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