Homebrew Spiderbeam, not using the commercial kit...

Ben/Anyone
If I did a seperate monobander for 6m, how far up/down the mast would it have to be from the SB? I have been reading up on interaction and it seems like the highest frequency elements nearly always suffer the interactions the worse. hence the 6m problem. I would think even the 10m elements on the SB would suffer somewhat.
Another Q, would seperate feedlines from each driven element to a remote switch, then down to one feedline to the shack (actually grounded entrance panel) also work? Seems this would prevent/heavily reduce the chance of radiating harmonics. This would prob change the placement of the driven elements and might change things too much tho??
If I wound up doing a quad instead, wonder how the addition of 6m elements would work. One book I was reading last night stated the highest frequency element would suffer effects of the interactions the worst. Actually the ARRL Antenna book and a book by "Haviland" on Quads both state this.
If I still do the SB, my back yard is only 30 ft, the combined spreader lengths would be about 32 ft, I would have to elevate one end or make other arrangements to have assembly room. Maybe assemble on the roof??
Also, I have been looking at Glen Martin roof mounted towers, I need to go talk to the permit folks about them.
Even then, maybe get my son in law who is a metal fabricator to build a tilting base for the Glen Martin??
Thanks Ray

 

Sounds about right. Unfortunately, I haven't come up with or had anyone provide me with a computer model of a spiderbeam so it's hard to predict reaction. Another ham on the spiderbeam yahoo group suggested to not place any other antennas or metal within 15ft of the spiderbeam.

I'm not sure about this but I'm sure someone on the spiderbeam yahoo group has probably tried it and could tell you.

Were you planning on using coax as feedline or something else? How would you plan to connect the wire dipoles to coax? The spiderbeam balun works awesome but all of the dipoles are fed with a single coax. The spiderbeam guys (Rick specifically) mentioned keeping the feedline geometry and spacing as per the guide in order to eliminate problems. He mentioned originally that the spiderbeam was fed with one coax cable to one set of terminals and all the dipoles connected to the single set of terminals but that this caused problems so they put 3 bands on one set of terminals and 2 bands on another set of terminals.

I need to try out 6m - I keep hearing how much fun it is...

I assembled mine mostly indoors because the components I used could be collapsed and then assembled elsewhere. I then took the spreaders outdoors to put them in the hub and guy them up. I simply extended the crappie poles and then secured each joint. I did this at about 5' above ground. It isn't a problem to elevate it because it is so light weight.

You can assemble half of the required length, guy it, add the wires to the "half-size" spiderbeam, then add on the rest as you raise it. If you use crappie poles, you can collapse the smallest diameter section and build the rest of the antenna first. This will reduce your length on at least one of the spreaders (maybe something like 32.5 x 25). Or you can also collapse the other spreader as well and build the antenna anyway. Then you would extend the crappie pole out, which would automatically tension all your wires at once (since they all connect to the same point at the end of 2 spreaders).

I did discover how tricky it is to guy it correctly as far as tensioning but if you plan properly, you can place your wires on the boom 1 or 2" closer to the hub than specified and then when everything is ready to go, slide each wire connection point 1 or 2" away from the hub and it tensions things much nicer and more evenly...

I had to tilt my mast over once to retension. It's NOT a tiltover mast! hahaha... This was a precarious process that I took very seriously and it worked out. With the beam at ~20ft, I was able to tilt the mast over and then it was easy to retension at the end of each spreader. I know of some really good plans for building your own tiltover mast if you don't want to buy one.

As far as a roof tower, they would be nice if you could drop the mast low enough to work on the beam as you stand on your roof. Even the antenna bracketed to your house would make it cake to work on - simply rotate it to mess with each section... As you know, wire beams are not without their ongoing maintenance. I wanted to bracket to the house but decided against it.

Ray, it goes without saying that I am happy enough with the spiderbeam that I don't want to use dipoles anymore. At best, you build it with exact precision per the guide and end up with an honest ~4dBd on each band for a cheap, lightweight antenna that can easily be replaced or repaired if broken. At worst, you get 5 separate rotatable dipoles at good height above ground. Either scenario is better than what I was using. Each time it needs repair I will simply improve the design.

At this point I just need to bump it up to 40' and then come up with a vertical or loop for 80/40 for my NVIS stuff...

 

Ben
Thanks for reply! I was planning orig to do the driven element/s connections per the spiderbeam plans, coax to balun, balun to ant. If I fed them with seperate coax I would prob have to use 3 baluns which would be a negative. I don't think that a (one) balun on the coax after the remote switch would work very well?? Most rigs should be pretty clean on harmonics anyway.
The plans for the tilt over mast sound tempting but would have a hard time tilting it over w/antenna attached at my QTH. The Glen Martins are self supporting, no guys, another expense though.
How are you grounding your antenna setup?
Sounds like you have a really super antenna going. Please continue to post your results up at full height. Barring a brainstorm miracle, about 35 ft seems max for me. Wish I could go higher tho. I just have to break down and visit the bldg dept at City Hall. I just got an Email return fm a ham in the metro area here but not in my city. He said the inspectors don't want a tower that would hit neighbor's property if it fell. Some munincipalities even require an engineering evaluation if the tower does not all ready have a CO certification. Very expensive!
Thanks for the assembly help ideas. I appreciate.
You have spent a lot of time with me and I really do appreciate.
Thanks Again!! Ray

 

Well, the plans I saw for the tilt over masts used a winch, which would make life much easier. Pretty cool ideas. Just loosen some guys and push a button? So I guess it just depends on your budget. You are right about name-brand towers.

The base plate has holes in it for staking the tower to the ground. I am using stakes through the base plate. I also disconnect coax when necessary. Nothing fancy but I will revisit the idea when I get some more time.

I've been and will be QRT for awhile while but I will check in as often as I can. It might be a month or two before I put the antenna at full height. ...We just can't seem to get through the spring storms. We will have another full day of 50mph winds again tomorrow.

Keep me posted on what you come up with.

 

Beam is still at only about 18ft and haven't had any time for radio. But a few minutes ago I took all of 2 minutes on the radio, pointed the beam westerly, and just netted a new one on 15m: V85AN. Cool.

Like I said before, the main difference between this antenna and my inverted V is that people hear me when I transmit. <-- I like this.

 

If there is one caveat about the antenna, or one complaint I have, it is that I have had to make adjustments to the guy strings more than once and it's still not where I want it. If tension is not right and you get an ice/wind storm, the spreaders can bend the toward the ground. This is the reason each spreader needs to turn up toward the sky a few inches.

Springs on the end of the wires would be awesome if they wouldn't affect tuning. This would allow automatic tensioning. Maybe instead, one could use UV-resistant bungee cord or something flexible to do the same thing.

 

This brings up a question I had tucked away somewhere in the back of my noggin' and just remembered; did you pre-stretch that Mac's line you used for the spreader guy lines, Ben?

Sounds like you didn't but it's something that could easily be overlooked in the excitement of building a SB.

I've never done so with my small and lightweight installations so far but something as big as a SB would require it (assuming you use Mac's Dacron line instead of the Kevlar or whatever the SB outfit uses with theirs. I would think the easiest way to stretch or pre-tension it would be to find a couple of posts or trees somewhere far enough apart to take all or most of the line and attach a big turnbuckle to one end. Then tighten it up well and leave it overnight that way if you can. Perhaps after 24 hours wth line will stretch enough so that when you use it to guy the spreaders it won't stretch anymore.

Sorry I didn't think of mentioning this before but like you, I was probably too absorbed in the other details of the antenna to remember that all Dacron rope/line will stretch a little.

I like the using springs idea; I wonder if there is such a thing as a tough UV-resistant plastic spring anywhere? Bungees might work for a while but the extra weight and vulverability might rule them out in the long run. Maybe some tough elastic covered with shrink wrap (UV/weather protection)?

Something to brainstorm about further...

73, Jeff (now QRT in KH6)

 

I did some prestretching but not on all strings. The main spans have been ok - it's the element guys and wiring that have slackened up some. One knot slipped on one main span. I fixed that today near the center post. Stuff out at the end requires me to lower the antenna and then use a tall ladder. Not fun. The next iteration of this antenna will be spot on. I have a list of improvements to make.

It otherwise works fine. I continue to work DX with it.

 

Just an update...

Lately, I haven't had more than a few minutes here and there for radio but if anyone is interested in whether or not the antenna works, it does. The antenna has been up for 1 month now and I have worked 36 DXCC entities with it. As a nice surprise, the antenna has also proven to be pretty tough. It has endured at least a dozen spring storms, many of which have brought 50mph winds to the area. It has survived one ice/wind storm as well.

However, when the antenna naturally settles and flexes, things seem to slacken up, at least with my home brew design. So I will probably take down the antenna so that I can adjust the guying. Hate to be off-air but it should be worth it to make improvements. The spreader/boom guying works fine but the wire elements have too much sag, which is a problem.

I had an idea to try out some shock/bungee cord as a way to manage wire element tension. Something like this perhaps:
http://www.dswrope.com/servlet/the-779/bungee-elastic-shock-cord,/Detail

I don't know how long it would last before failing but if it would last 1 season at a time, it might be worth experimenting with. I could also have redundant regular rope tied as a backup. Don't know of anyone having tried this, especially with a spiderbeam, so why not?

 

I sure like that marine grade uv-resistant shock cord idea. I think you're onto something there, Ben as it does seem like a solution for a season or two at the very least.

Maybe when you take the SB down to install it you could take some closeup pix detailing how you incorporate it into your design.

73, Jeff (back to packing and loading, packing and loading...)