The New Spiderbeam @DL2LSM

The Taming of the Shrew

I’ve been able to operate the station of my dad (DL2LSM) on several occasions during major contests. The antenna is a 2-by-20m dipole about 20m agl. It works quite well on the low bands up to 40m. It can be used with good results on 20m too. However, it isn’t as great anymore on the higher bands. Therefore, we decided to get a beam up in order to improve the situation on the higher bands.

The most important features a good antenna needs are:

  • high gain and good front-to-back ratio
  • small footprint
  • durability
  • leight weight
  • low price

The perfect antenna is still to be developed. However, a good compromise seems to be the so called Spiderbeam. I have been using the portable version of this antenna during the WPX CW 2013 in Denmark. the three band version is in principle an interlaced 3-3-4 element three bander for 20m, 15m, and 10m. It should be noted that I’m absolutely not interested in the WARC bands and will mostly operate the antenna during contests. The antenna offers good gain for a relatively moderate price. The only weak point I see are too much mechanical compromises which will lower the long-time durability. Therefore, a few technical changes have been introduced in the system in order to have it up in the air for a long time.

Making Space

The Spiderbeam should be mounted at least 10m high in order to give a good performance. Therefore, the oldest mast located directly at the side of the house is a good choice for the antenna. It is about 15m high and can be turned from the inside of the shack by a crank located directly at the operators position. However, the mast needed to be lowered and the old antenna needed to e removed. The later was a 2-by-6 element vertical system for 2m mainly used for repeater work. However, repeaters are only sparsely used nowadays. So, it isn’t a huge sacrifice.

The work has been done on 2013/08/17 and took us (DL2LSM and me) almost a day. Everything went quite well when we took down the antenna and prepared the mast for it’s new load. A few pictures can be seen in the following gallery.

Assembling on the Ground

Due to its size antenna assembling is best done on ground level. It hasn’t been very easy to find a suitable spot where the required square of about 7.5m-by-7.5m is not obstructed by any bush, tree or other obstacle. Eventually, we set it up in the middle of several trees. There hasn’t been much space around.

The following changes have been done in order increase the mechanical stability and durability:

  • All guy lines have been connected to the spreaders by snap hooks. The latter are attached to guy rings fabricated from M44 standard washers.
  • Four guy lines in the horizontal plane have been mounted on the outside corner of the spreaders. So, there are two guy levels in the horizontal planes.

Getting it up

The only option to get it towards its final place on the roof was to tilt the antenna into a vertical position. In order to do so we had to cut quite a number of  branches from several trees. However, we managed the task and were able to slowly move the antenna to its mounting position. This process has been very time consuming and consisted of the following steps:

  • Moving it up to the roof top.
  • Moving it towards the mast along the roof top. DL2LSM crawled along the top of the roof slowly moving the antenna forward. DK3WE opened the front snap hook with all the guy lines and the driven element for 20m to allow to slip the antenna along the mast. During that procedure the 20m had been dislocated from the spreader and needed to be repaired.
  • Mounting the antenna to an extra prepared crane fixed at the lower mast segment and moving it upwards and settling it into the top mast segment.
  • Exchanging the guy wires for stainless steel ones.
  • Cutting a number of tree branches.
  • moving the top mast segment upwards.

During this process Murphy visited us a couple of times:

  • The 20m driven element got dislocated from the spreader when the antenna has been slipped horizontally along the mast. Has been repaired from the roof top by rotating the antenna 180 degrees and lowering it quite a bit.
  • When moving the antenna up the snap hooks caught the guy lines from another mast. To free the Spiderbeam took a couple of hours and included some additional tower climbing.
  • The coaxial cable got stuck and its insulation has been cut. Has been repairable with some insulation tape.
  • When checking the VSWR finally we have been realizing that the driven element for 20m is much too long. It resonates at about 13400kHz. Most likely I have been cutting 574cm instead of 547cm :-(. We decided to leave it that way and work with an antenna tuner on 20m.

First Impressions

The first QSO has been on 15m CW with Oliver, V44KAO on 2013-Aug-29 at 21:27 still with the antenna at about 11m agl.

vswr_spiderbeamAs mentioned above the VSWR is about 1Mhz too low on 20m. It is a bit too low on both on 15m and 10m, respectively. This is due to the effect that the driven elements have not been optimized after the beam has been put in place. This is simply due to the fact that there hasn’t been any possibility to get to the appropriate places to do the job.

In general, the signals of the beam are about one to two S-units stronger on the high bands compared to our 2-by-20m dipole. Additionally, it picks up much less noise, i.e. the signal-to-noise ratio is even better. The antenna shows a clear directional pattern even when using it on 20m with an antenna tuner connected. Exact values of the front-to-back ratio are a bit hard to determine because of the lack of reasonable measurement equipment.

Finishing the Installation

There has been a good opportunity end of October 2013 to fix all the flaws induced during the initial setup of the antenna when a number of dead trees needed to be cut down on the property. A platform lift has been rented in order to do that job. Additionally, it has been high enough to reach the antenna and do the following improvements:

  • The 20m driven element has been cut to the length specified.
  • The horizontal guy lines have been replaced by 2mm PVDF Monofil.
  • The direction of the snap hooks have switched in order to avoid further line and rope catching of adjacent antenna installations. The hooks of the upper guy lines havn’t been changed. They have been secured by heat shrinking tube instead.
  • The GFK tubes have been cut by about 10cm in order to gain some more room around the beam. 
  • The mechanical tension of 15m driven element has been checked. So it is not to tight and allows for some tube movement. However, if the upper guy lines stretch or the connection looses they might be at risk.
  • The VSWR on all bands has been optimized.
  • The cut in the coaxial cable has been sealed with a few additional layers of self-vulcanizing tape.
  • The rubber cap at the upper guy position of the mast has been repositioned for better movement.
  • Some more tree branches have been cut to allow free movement when lowering the antenna at a later point in time.

The weather has been extraordinary sunny and absolutely calm. Therefore, the work could been done in less than a day. Nevertheless, working on a free standing platform in a height of about 16m is not for everyone.  it took quite some courage to overcome the fear of height.

vswr_spiderbeam_repairedThe VSWR plots shown have been determined with a following the optimization of the driven elements. The VSWR on 20m and 15m stays now below 1.5 across the entire band, respectively. So, this is absolutely perfect in my opinion. It looks a bit different on 28MHz. The VSWR increases over a value of 2 for frequencies above 29 MHz. The reason for this behavior is not known. The curves given in the data sheet give a much flatter characteristics. Therefore, a antenna tuner will be needed on these frequencies. Nevertheless, there won’t be any limitations with the CW and SSB operations planned with the antenna.

Technical Details

There have been some technical improvements to the original Spiderbeam design (hopefully) in order to improve the lifetime and duration of the antenna. They are described here briefly.

  1. The heat shrinking tube has been exchanged for a type with internal glue. This should give a much better mechanical stability of the driven elements.
  2. Two 1.5mm holes have been drilled in the bottom of the common mode choke housing in order to allow any water condensing inside to escape.
  3. The PL/UHF type socket of the common mode choke housing has been exchanged by a N-type one for better shield and mechanical connection, respectively. Additionally, the mechanical joint has been sealed against water by a heat shrinking tube with internal glue.
  4. The ground connection of the common mode choke has been made by soldering the braid of the coaxial cable to the N socket via a thick silver coated copper wire. This should give a better and longer lasting connection than the one via solder lug suggested.
  5. The clamps holding the center plate to the mounting tube have secured against turning with an additionally 6mm screw.  The mounting tube is only 1″ in diameter and I have been afraid that the clamps do not provide enough friction to prevent the antenna from slipping.
  6. img_2174_smallThe 1mm PVDF Monofil used for the horizontal guying of the antenna has been replaced by 2mm ones. The material is normally used as leader line for game fishing. It is horribly expensive. However,  I have much more confidence in the mechanical stability of the material. Tying knots wouldn’t be an easy task. Therefore, the line has been crimped at the snap hooks. The principle is shown in the picture. Please note that the sleeve isn’t crimped yet. (Proper sleeves and a professional crimping tool is needed. Additionally, the recommended crimping process should be followed. Ask if you need any details.)
  7. p1130193_smallWe haven’t found any method to tie all guy lines as well as the elements to the end of the boom tubes in a way that they might last for long time. Therefore, we decided to use M42 washers with additional holes and snap hooks. Additionally, tying knots with stronger PVDF monofil material is not an easy task. So, we used crimping sleeves to do those connections. It has been another major investment into a professional crimping tool. However, the connections done are look really pretty and will hopefully last.
  8. img_2172_smallThe following method has been used to connect the PVDF monofil to the insulators (black plastic pieces). It needs two crimping sleeves. The line is run twice through the hole and then through the first sleeve. The loose end gets a knot and runs through a second sleeve. This connection can’t open itself except the crimping sleeves (or the line) break.
  9. p1130191_smallA knot in the middle of an elements prevents it from sliding out of the clamp fixing it to the boom tube. It should be taken into account that this will shorten the element slightly when cutting these elements.
  10. The outside boom tubes made of fiberglass have been shortened by 10cm. This gives a slightly smaller turning radius which could be important when lowering the antenna again.

Additional Pictures of Antenna Details:

The following is just a Gedankenexperiment and not been proven experimentally. However, we think it might be a good idea: For best mechanically stability and least tension in the system just let all the boom tubes follow gravity and let them bent slightly down when assembling. Then fasten the lower guy lines just a bit and secure with the upper ones. The sag shouldn’t be to much and the system tension will be greatly reduced. This is especially true for the upper guy lines which have to hold quite a lot when the boom tubes are straight.

Final Thoughts

I would like to thank my family for their great support when setting up this monster antenna. A special thanks goes to my dad, DL2LSM, who helped a lot with this installation. There wouldn’t be this antenna without him.  Additionally, I would like to thank Rick, DJ0IP, of Spiderbeam for his technical advice.

The setup time of  such an antenna should not be underestimated. In my opinion the system is not optimized for permanent installation when setup as directed and used with the materials originally delivered. It has a few weak points we tried to overcome. So, we hope that the antenna stays up for a long long time and doesn’t need maintenance soon. The first real test will be the CQWW DX CW 2013 when I will start in the QRP Single Operator Assisted Category.

If you plan to built such a system yourself and need some advice or want to use some tools we have been using please do not hesitate to contact us. We will gladly help you if our time permits.

This entry was posted on Tuesday, August 20th, 2013 at 10:51 am and is filed under Technical Article. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

5 Responses to “The New Spiderbeam @DL2LSM”

  1. DK3WE » Blog Archive » Winter Impression @DL2LSM Says:

    […] picture of the spiderbeam has been taken December, 29 […]

  2. DK3WE » Blog Archive » Spiderbeam Repair Says:

    […] storm ‘Niklas‘ caused some minor damage on the spiderbeam. One of the lower guy lines got disconnected when a carabiner […]

  3. DK3WE » Blog Archive » CQ WWDX CW 2013 Says:

    […] all weekend long. Unfortunately, the bands down to 20m died right after sunset on both days. The new spider beam works excellent. I got through almost on all pile-ups except on 10m where the hell was loose. So, […]

  4. DK3WE » Blog Archive » VA6AM Triplexer Says:

    […] order to use the spiderbeam @DL2LSM in parallel on several bands I’ve been looking for a triplexer. Looking at several approaches […]

  5. DK3WE » Blog Archive » Antenna Survey @DL2LSM Says:

    […] three band spider beam at a height of about 13m, […]

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