ON7RU의 자작 HEXBEAM

[HL2UOK]

History	Baseplate	Centerpost	Spreaders	Wires & cords
Building	SWR & tuning	Do's & Don'ts	Installation	Reference

History

Lately I moved to another QTH. Because I can't install a big tower right now, I picked up a used 9m tower. An iron tube
will give me another 3m. My goal was to install an antenna with a small footprint, with some gain and directivity. If possible 5
bands and the antenna should be able to handle QRO (800w).
Because it's temporary I wouldn't spend to much money, so the hexbeam seems to be the ideal solution.
I did some research on the internet and found several websites that helped with designnotes, hardware tips, ....
The word got spread in the clubstation and there was a very positive drive to help and to review the ideas.
Serveral chatsessions with co-builder, ON3TD en Patrick, ON4CLQ (hardware expert) resulted in a "let's go" early
November. The goal is to build it First Time Right. It should be broadband and able to survive 90km/h wind.

Baseplate

I had lot's of ideas, but there's a point where you have to start building. One day I received a mail from Patrick, ON4CLQ, he
build the baseplate, wow what a surprise. The baseplate is aluminium, the flence is Inox. Strong, light and well built. Thanks
again Pat. Don't forget to drill a hole in the baseplate for the coaxcable.

Baseplate (under)	Baseplate (support centerpost)

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Centerpost

For building the centerpost you need a PVC tube of 120 cm and 4cm in diameter. drill 10 holes to install the srews which have to
support the dipoles. The angle should be around 60degr. but is not critical.
Here comes some math in placee. If your PVC tube is 40mm diameter, the perimeter is 40mm x π (3,1415) = 125,66mm
60degr means 1/6th of a circle. So pulle a straight line on your PVC tube. The other 2 lines (+30° & -30°) should be at
125,66/12 = 10,5mm. I used M4 20mm inox screws. Here you find the distances from the screws to the baseplate.
Here begins the serious part. Before you start (trying) to insert the screws make sure there are no woman, children or guns around.
I made a usefull tool from an iron coathanger which helped me a lot and saved me from some extra grey hairs.
After stumbeling for another 10 minutes I putted a mark on the coathanger to have an idea of the distance. When this trick was
applied, all screws where fixed within 5 minutes.
When the screws are in place you can start to built the coax feeder. Foresee at least 2 hours to accomplisch this job. You need
1,2m 50ohm coax, 16 cable shoes, a good cutter, and a solderstation.
Because I want to run QRO I used RG213. If you plan to stick with 100W, RG58 will do just fine.

Holes are drilled, the "easy" 10m screws ones are fixed	Tool to fix the screws
Finished...yes....	Foresee about 2 to 2.5 cm for easy installation
Coax connections in detail	Centerpost finished

Adding PVC for a perfect fit	Top of centerpost, used to attach support wires

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Spreaders

Spreaders can be made of several materials, some use fiber glass tubes, others use bamboo but most popular here in europe
are the crappy fishpoles. They're quite cheap, I paid 5? each. I consider looking for a 5m pole, so you gonna have to remove
the topend and eventually remove a part at the base. When you slide out the elements make sure they fit pretty tight.
To keep the fiber elements fixed I added silicone base glue (TEC7) on all joints.
As said before, these are crappy fishpoles and they might be the weakest link of the antenna. Try to find some alu-tubing to
re-inforce the base of the fishpole. Forsee about 30cm. I as lucky to find a perfect fit....an old destroyed A3WS did the job.
Then cut the fishpoles on the right length. I'm building the broadband version, the min. length is 353cm, I took 355cm.

6 identical fishpoles	Remove unneeded parts
Add silicones to all joints	reinforce the crappy fishpole with alu-tube (30cm)
Make sure they all have the same size	I used this tool to cut the fishpoles.

Support for the S-hooks.	I

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Wires & cords

A couple of months ago I found some nice lengths 1,5mm2 and 2.5mm2 for a good deal. I Decided to use the 1.5mm2 to reduce
weight and windload. Make sure you have the right lengths. Measure twice, cut once. I advice to cut the reflectors first. If you
make a mistake you can reuse/recuperate the lengths to cut the drivers.
All reflectors where pre-assembled with cable shoes and tip-spaces.
Not affecting the performance, but needed to complete the project are the support cords. You need at least six (from top spreader
to centerpost) but I made 12 pieces. The 6 additional perimeter support cords have to be looped over the ends of the spreaders.
The length of each cord is 328cm, S-hooks included. It's very important to use UV resistent cord with a low stretch factor.
Some builders use the 20m dipoles & reflector as perimeter support, but I didn't want to stretch the VOB cable.
For the tip spaces I used the same wire as the support cord. The length of the 5 tipspaces is available in the table at the bottom
of this page. Make sure you add at least 10cm, it allows you to run the wire twice through the electrical connector for more
security.

Dipoles & reflectors	Connections tip space & reflector

The length of all wires & tip spaces. Remember, the driver consists of 2 sections (dipoles) and the reflector consists of one section.
All sizes are in centimeters. 2,54cm = 1 inch.

Band	Freq	Length 1/2 driver	length reflector	tip space	distance screws above base plate
20	14.150	553,7	1046	61	15
17	18.100	430,5	815,3	47	25,5
15	21.250	367	697	40,5	35,5
12	24.950	309,1	589,3	34,3	51
10	28.400	271,3	519,2	30,5	106,5

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Building

Once all parts are ready you can start assembling the hexbeam. Put a pole in the ground where you have some room to
assemble the beam. If you can't finish the project in one day, make sure it's on a safe place for kids, woman and mothers in law.
Before insirting the spreaders into the baseplate, I added rubber boots to prevent cracking the fishpole while tensioning the U-bolts.
I used fuel-flex, costs about 5eur/m. It was a little to small so I had to cut the boot in half.
Insert all fishpoles and put some tension on the U-bolts. Now come the support cables in place, start with the six supportcables
between the end of the spreader and the centerpost. Slip the S-hook over the screw at the end of the spreader and attach the
other side on the centerpost. Don't work clockwise, always take the opposite spreader to prevent bending the centerpost.
When the six main supports are installed, you can start installing the 6 additional support cabels between the top of each spreader.
Here I worked clockwise.
 

rubber boots	Spreader 1, see cartonboard with support cords
Hex-shape	Ready for the sky

When all the support cords are installed,and all cords have the same tension, you should have a very symmetrical construction.
Time to install the drivers & reflectors. Start with the 20M band. So far everything went smoothly, but at this point I found my
first issue. Seems there's a bit to much bow and I had to move the hose clamps up to the edge of the fishpole.
Lucky me I cutted the the fishpoles @ 355cm and not 353, the minimum length. There's still a bit slack on the wires, but that
shouldn't affect performance. When 20M is fine you can start installing the other bands.
If you have to move the hose clamps make sure you move them all for that particular band.
To protect the fishpoles from cracking while tensioning the hose clamps I wounded some tape on the fishpole on these particular
places. I advice you to wait with the tape when assembeling the fishpoles, because you propably have to move the clamps a couple
of cms. To support the wires I used plastic straps. Use the black ones, there UV resistant, I advice a minimum width of  5mm.

Attaching drivers to centerpost	tape, hose clamp & plastic straps

Keep the 10m driver as tight as possible to the FP

Tip space twice through connector (I'm a lazy photoshopper)

Teammember ON4ATA adviced me to solder all cupper joints from the coax-pieces attached to the centerpost.
This had 2 advantages. It prevents the coax sucking weather when raining and it allows the silicons to stick better on the surface.
In the DIY shop they told me cupper rejects all kinds of silicons.
Other pictures show how the drivers & reflectors are attached to the fishpoles. The last picture shows how I connected the tip
space to the driver. I propose to put the wire twice through the electrical connector for more secure connection.

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SWR & Tuning

When all drivers & reflectores are installed it's time to connect the transceiver or SWR analyzer. Lucky me, our clubstation has
the popular MFJ259, thanks ON4EKO. The antenna got raised on an old boom and the first test was done @ 4m.
The results were fair, but with a little tweaking I should be able to improve the SWR results.
On 10 & 20m the dip was to low, so I had to cut the drivers a couple of cms. To calculate the new length and the difference you
can you use this formula : New wirelength = old wirlength X (old frequency / new frequency)

For example:  553,7 (driver 20m) X (13.800/14.100) = 542, so I had to cut the 20M driver 12cm.
 

SWR results for the HEXBEAM @ 4M and after tweaking at final heigth @ 12M
20m - 14Mhz	Remarks
	Initial dip was @13.8, so I cutted 12 cm and found great SWR curve at final height. Good front-to-back Didn't changed the length of the reflector, not for this band, not for any other.
17m - 18Mhz	Remarks
	SWR seemed OK @ 4m. Once on the tower best SWR is at 17.5Mhz. When the antenna has to come down for maintanance I'll tackle this issue.
15m - 21Mhz	Remarks
	SWR seemed relatively OK on test height. , only removed 2cm of wire and got good results. Antenne seems to get more broadbanded when rising. When maintaining the antenna I will try to shift the dip a few 100Khz.
12m - 24Mhz	Remarks
	nothing to add here. Had to remove 6cm from the initial length and got flat SWR accross the band. Initial dip was 1.1 @ 24.4Mhz
10M - 28Mhz	Remarks
	First I taught it was tricky to remove 8cm from each driver but result is a great SWR curve. SWR doesn't reach 2.0 before 29.6Mhz Initial dip was 1.2 @ 27.3

Does it work?

Well, the last few days in a limited timeframe I managed to work K5D on 17 & 20M both SSB & CW, 9Q, 9K, J7, K4A, ...
The answer is definitely YES

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Do's & Don'ts

Make sure the screw on top of the centerpost is long enough to support the 6 S-hooks
Don't cut the fishpoles at the minimum length, foresee some extra cms.
When attaching the wire to the cable shoe, make sure you solder it close to the end of the cable shoe.
For maintenance reasons I advice you to cut the 50ohm calbe just above the RF-choke. This allows to thake the antenna down
and leaving the coax at the tower.

I'll complete this list when things come to mind.

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Installation

It's light but remember it's size	Don't try this at home.
Tilting the hexbeam	Securing the hexbeam

Ready to werk DX	The black spot  under the hex is the RF choke

References

G3TXQ - the inventor, K4KIO - The reference for builders, DL7IO - some good design tips
PG3N - good ideas and PA2JJB some good ideas as well.

Special thanks to Patrick, ON4CLQ for the baseplate and the welding of the flence, ON4EKO for the use of the SWR
analyzer,  my father in law Rudy for his tips & tricks with the mechanical construction and help with testing and installation
of the antenna. Last but not least my girlfriend Kelly who's supporting me and this wonderful hobby.

[DS3GLW]

이사람은 절연 전선을 썼는데, 나중에 튜닝할 때는 driver 엘레멘트만 잘랐습니다. 이게 SWR은 맞추줄 수도 있지만, 전체적은 성능에는 나쁜 영향을 줄 것 같습니다.

[HL2UOK]

당근 리플렉터도 같이 짤라야 되는데.. BB타입은 훨씬 크게 보이는 군요 전체적으로 50센티 정도가 긴데