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Homebrew Spiderbeam, not using the commercial kit...

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AE7F, Jan 4, 2012.

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  1. AE7F

    AE7F Ham Member QRZ Page

    In looking at various antenna designs and many DIY ideas, I have come back to the idea of the Spiderbeam. As in other threads, I would like to make my own antenna. In consideration of this, has anyone built a Spiderbeam without buying the kit?

    I've compared spreaders in another thread:
    http://forums.qrz.com/showthread.php?327590-Spreaders-Spiderbeam-vs-MaxGain-Type-1-which-is-stronger

    I think the MaxGain Type 1 spreaders would be stronger and less expensive. This is what I have found so far in terms of a DIY, 5-band spiderbeam:

    rope & wire
    ---------------------
    47 + 15m = 62m kevlar used for guying the spiders: ~ $37
    82 + 22m = 104m dacron used to support wire elements: ~ $41
    73 + 30m = 103m of wireman cq-532: ~ $64

    spreaders
    ---------------------
    4 type 1 spreaders from max gain: ~ $100

    spider
    ---------------------
    1 spider - cast, custom, or Cubex: ~ $60

    This comes to around $300 not counting shipping or other parts such as clamps, bolts, etc. Call it $400 shipped. In contrast, the commercial kit would cost around $650 shipped.

    One could save about $30 by using different wire, such as (http://www.homedepot.com/Electrical...splay?langId=-1&storeId=10051&catalogId=10053) and around $80 if using (gasp) PVC pipe.

    The use of PVC is generally discouraged for spreader use but PVC does have some good points. It's cheap and easy to replace. It's easier to work with as well. You can replace your PVC spreaders probably 4 times before you've spent the same amount on PVC as you would have on fiberglass. And by the second or third time, I think you would have the weaknesses worked out to where you could prevent future problems. If you have a crank-up tower, the maintenance/replacement issue is far less of a problem and might even be considered to be a non-issue. Unlike when using fiberglass spreaders, the guy system would have to take most of the weight of the spreaders because fiberglass spreaders can support themselves to a point but PVC would sag too much. However, the Kevlar rope should do the trick. One would also just add more guy points.

    Also, in the Spiderbeam design, you can keep the spreaders horizontal if you want. In contrast, the hexbeam design stresses the spreaders upwards and PVC really sags. I think it would be much harder to maintain hexbeam geometry with PVC than to maintain the horizontal geometry of the Spiderbeam with PVC. I have conversed with some hams who have used a PVC hex design with some success. Breaking doesn't seem to be the problem (due to high flexibility) but sagging is a major problem. This could be dealt with much better on a Spiderbeam.

    Nevertheless, a $400 dollar DIY Spiderbeam that uses the MaxGain Type 1 spreaders sounds interesting to me.

    What do you guys think?
     
  2. NH7RO

    NH7RO Ham Member QRZ Page

    Hello again, Ben; I suppose you've already done your homework obviously but am wondering if one really needs that much rope for a 5-band Spiderbeam? 166m=540 feet or thereabouts. Since I'm also currently leaning towards a Spiderbeam (either DIY or "storebought") I suppose it's time for me to download their construction manual and look into it further myself. Your recent 5-band antenna comparison was very helpful and I again note that the Spiderbeam has the highest db per pound ratio of the different beams you put in your comparison. While a bit larger than a hexbeam it is still in the same weight class and cost but has a tad more gain. Groovy!

    What I might do if I DIY one of these is use this rope as I've used it for many of my antennas already and I like it a lot:

    http://rwrope.com/outdoors-sporting-goods/sportsmans-utility-cord/sportsman-utility-cord.html

    A 1000' spool of the 150# test runs $35 and maybe $5 shipping=$40 total rope cost (or 6 100' spools would be only $24 + shipping so maybe $30 total rope cost). Although their website indicates polyester I'm thinking it must have some Dacron in it as it handles like Dacron and weathers very well. An added plus is that it's strong, cammo green and is nearly invisible since it's so thin (approx 1/16" is my guess).

    That link to the Home Depot wire is the 18 ga. stranded I mentioned in another thread; it's a good deal in my opinion and is also probably what I'd use as well.

    As for the spreaders I think it would be best to stick with MGS Type 1s or 1Ls unless you really wanted to make one of these beams on a tight budget. PVC may work (with enough guying support) but the weight and extra guying wouldn't be worth the slight savings in my opinion.
    I'd actually be tempted to try out the lighter 1L spreaders to keep the overall weight down as low as possible, too.

    I already have an old New Wave Portapole 33' aluminum telescoping mast that would put my beam up around 30' in the air. Naturally, I want to go with something as light as feasible so as not to overstress my mast as well as be easily raised and lowered by myself if necessary. I currently have my 10lb 17M Moxon on it now and it is guyed at the top and about the 10' level. I really like the mast and hope that it would still be OK to use it for a monster Spiderbeam. I see on the Spiderbeam website that their standard 5 bander weighs 16lbs and the HD version is 25lbs. IIRC.

    As much as I like the KIO/DXE hexbeams I am a lot more tempted to try a Spiderbeam instead. The big wire log periodics would probably be more difficult to build and manage than a Spdrbm, at least in my mind.

    Thanks for starting this thread and I hope you elicit further response. I've also joined the Spiderbeam Yahoo Group which seems like another good place to get feedback, too.

    Now it's on to a bit of research on costs such as for the hub---I see that the Spdrbm people use a flat aluminum plate with stainless U-bolts (nothing fancy) so there's another item that could easily be homebrewed at minimal cost. I've been saving an old table saw's top that that I have out in the back shed for such a project---it is made of thick aluminum that'd be perfect for cutting down and drilling!

    73 until further ruminations come to mind,

    Jeff NH7RO
     
  3. NH7RO

    NH7RO Ham Member QRZ Page

    Just realized that spiderbeams (I'll abbreviate as SB from now on) require a balun at the feedpoint so we better budget that into the total cost.

    Although the SB web site has the W1JR type coax choke baluns for $75/$119 (kit/built) I suspect that is something that could also be easily homebrewed and installed in a small PVC junction box with the proper toroids and teflon coax. Either way, it's another cost and essential item that shouldn't be overlooked.

    One other thought as long as I am here is: What about adding 6M to a SB? Has it been done by anyone with any success? That's one thing I do like about the KIO and K5BOB hexbeams; they have the option of a 6th band/6M.

    It would add to the weight, cost and complexity so it may be preferable (at least for me) to build a separate 6M monoband SB instead. Since I already have a 5 el. Yagi for the Magic Band I would be more interested in attempting a 6, 7 or 8 element SB at some point. In the meantime, it doesn't hurt to dream or start planning.
     
  4. AE7F

    AE7F Ham Member QRZ Page

    We must be on a nearly identical frequency. About an hour ago I thought about the cost of the balun and also 6m add on to the SB....

    I have indeed been through the specs document as well as the construction guide for the SB. Their dBi quotes are strange but the dBd gain quotes seem about right for what they classify as a yagi design. The construction guide is a bit strange and that's one criticism you'll see on eHam reviews. If I use their guide, I will actually digitally edit the .PDF file for my own use so that it makes more sense to me. I will move around the tables and specs so that they are in a logical order that makes sense to me so that I don't get things wrong.

    The balun can definitely be done yourself. IIRC, they have a line or two in the construction guide where they talk about the balun. However, I think there is mention of just using slip on choke beads as well. Also IIRC, many of the hex beam guys use the choke beads. Also of interest is that my antenna tuner has a built-in 4-1 balun. Some tuners do. However, there is a reason they put their W1JR type balun up at the antenna itself! There are probably many ways to accomplish the choke balun so yes indeed, it has to be included in the cost but I think there might be $25 or $30 dollar savings to be had here...

    I haven't asked about 6m but I did ask the SB group about stacking an 11-element 2-meter beam above the SB. Didn't have a response last time I checked. I'd like a 6m addition myself but I'll settle without one for now if I have to. 5 bands means a ton of wires.

    The Titanex DLP-15 I looked into also had 40m on it as well. I still never could figure out which wire was the "full 40m dipole" on it though....

    I am a member of the SB and HB groups and both have been very helpful, but I think there seems to be more people and responses on the HB group. It's my intention to use tips and tricks from both antenna designs on my own.
     
  5. AE7F

    AE7F Ham Member QRZ Page

    Glad we are looking at the same thing and thanks for your continued input.

    Okay, thanks for that rope info. The fact that you've used it before is a useful bit of information. I dig the almost invisible part. With that much length, you could guy the heck out of the antenna. I will for sure consider this and the HD wire as well.

    Well, I can set the budget to whatever within reason, so the PVC idea is more of a strong curiosity. As mentioned, I have talked to several who have made/are making it work on the hex beam. The one thing I don't know is how much heavier a 15ft section of PVC is than fiberglass. I do know that I can get all the PVC I want locally without shipping, so $20 bucks buys me enough for the job. Then I thought, that's the shiny white stuff for underground use and it would look ugly and so forth. So I priced the grey UV and corrosion resistant electrical conduit PVC and it would cost me about $30 bucks. It was in 10ft swaged sections, which might be a dealbreaker for me, but if I can get it in 15 or 20ft lengths, I am strongly considering trying it. My mast is strong enough to hold the weight and I can crank it up and down, so I can bring the mess down if it doesn't work.

    But think about how easy it would be to mess with the SB design when using PVC. You can put holes anywhere in the PVC without as high a risk of splitting. For guying, you could put an eye bolt right through the PVC with a nut and washer on one side, then simply guy to the eye bolt. You could pin any jointed sections. Or you could skip the eye bolt and just run the element wire or guy rope right through the PVC mast (of course I would also use a bushing to prevent freying or snagging of the rope/wire). I haven't worked with fiberglass but I don't think I'd want any cuts, knicks, or holes anywhere that it wasn't absolutely necessary. You can always still use clamps but if the PVC sections are full, jointless lengths, and if clamps cost more than nuts and bolts.......

    The PVC would definitely have some sag. This is a real issue. But a certain amount of flexibility might... might help in the kind of wind we have here. Don't know, I've never had a PVC spreader up in the air! I think the sag would really show up when you guy around the perimeter to make (when viewed from above the beam) a diamond shape.

    However, with the cheap rope you posted, you would have so much, and with it being such small diameter, just double the guying. I would prefer thicker stronger rope but with that diameter, I may not mind the extra guying if it's easy on the eye due to its small size anyway. Dunno, just thinking aloud.

    For your location, you probably could use the lighter materials. Here, they would most certainly blow apart in the spring winds.

    Ditto. This is exactly the conclusion I came to. Having some people who have already tried out a design yields more confidence to try it yourself, albeit at least myself, with some (possibly strange) design changes..

    The hex guys have used everything from plywood to the bottom of a wooden wire spool to ... you name it. The SB kit includes plate that is only 2mm thick but it sandwiches the spreaders between two that are bolted together. The mast clamp bolts to the flat plate. One eHam reviewer said the clamp bolts would shear off when the beam torqued in the wind. He just used larger bolts and I think additional clamps.

    I've seen a few hex hub plate designs, one of which was simply a large plate of 1/4 inch aluminum and you would just use 2 clamps per spreader. No sandwiching the spreaders and such. Not an engineer so I don't know which is better but I do know you can get a plate of aluminum for $25 bucks. Just drill the appropriate holes and add 8 clamps and voila. This design would probably work best with a "floor flange" on either side of the plate, which flanges are bolted to your antenna mast.

    Or there are the cubex spiders or the custom spiders made by Rick Adams (rickadams.net). Biggest challenge is coming up with one that fits the spreaders of your choice. That's why I may have to just use the aluminum plate + clamp method, which can easily adapt to the proper size.

    If I were to choose PVC and it fails quickly and catastrophically, I will be the first to come back and laugh with everyone else. But if I use it and it works....
     
  6. AE7F

    AE7F Ham Member QRZ Page

    Home Depot wire: $24 (no shipping, local)
    inexpensive rope: $45
    kevlar rope: $45
    UV resistant PVC spreaders: $30 (no shipping, local)
    spider hub plate assy: $75 for aluminum plate, 8 clamps, 2 floor flanges & bolts (no shipping, local)
    choke balun: $50? for DIY (don't know, never made one like in the SB manual)
    tuner balun: ($0 - included in tuner)
    -----------------------
    $269 as above, or $339 with MGS4U Type 1 spreaders.

    This drives the cost per average dBd of the SB down to $66.25 or $83.49, depending on spreader type used. See: antenna comparisons.pdf

    If either of the above configuration would survive the WX here, for that price, it would be a killer bang for the buck - much better than any of the other antennas I compared. The key is whether or not it would survive because the electrical design would certainly work well enough.
     
  7. AE7F

    AE7F Ham Member QRZ Page

    As far as experimenting with PVC spreaders, this obviously would make quite a difference as well:
    Schedule-40-versus-Schedule-80

    Depending on the weight, it looks like Cantex Schedule 80 Conduit would be much better than Schedule 40 water pipe:
    Cantex Schedule 80

    Sold at local Home Depot Stores:
    Cantex Sch. 80

    Is UV, flame, and crush resistant and has a specified temperature range of -20f to 122f:
    Cantex FAQ

    You would have to find an OD that would work with preexisting spider designs but if you design your own hub, you could use any OD of the stuff and make it work.

    And finally, grey is much better aesthetically than white! :D
     
    Last edited: Jan 5, 2012
  8. KC8VWM

    KC8VWM Ham Member QRZ Page

    Using PVC is actually very heavy and it sags considerably in runs longer than 5 feet because it is not "stiff"

    Epoxy resin fiberglass fishing rods are very strong and yet lightweight by comparison. Thier only downside is they are not very "crush" resistant.

    However, I will attempt to visualize and present a few ideas in this thread for consideration using some of my own past antenna contruction photos.

    Here's a lightweight hub which was purchased at a local farm supply store. These are actually lighter than the idea of using heavy steel clamps installed on a chunk of aluminum plate but yet serves the same purpose.

    a20791612c1805091e7d8f_m.JPG


    The hub I am using is basically originally intended to hold 1" diameter poles together to construct a frame. The frame, when constructed can hold a tarp, green house or similar temporary shelter of some kind.

    They are very sleek and lightweight, but yet very strong and rigid. They are well designed and originally engineered and intended for erecting structures involving weight bearing structural stress. They are also well suited for long term use in outdoor enviroments.

    These also happen to hold fishing poles for constructing antenna's quite nicely too. [​IMG]


    [​IMG]

    The photo above and below shows the hub which is to remain permanently attached to a short mast section. The short mast is simply slid into a longer lightweight mast and so no clamps on the hub are ever required to be removed, disassembled or reinstalled during setup or takedown operation.

    Hub permanently installed on short section of lightweight aluminum mast. Poles can be removed from hub for storage. No tools are required for assembly/ dissasembly.

    [​IMG]

    To raise the antenna higher, we simply add the desire amount of lightweight aluminum mast sections.

    [​IMG]

    The ends of the fiberglass rods have been taped to help protect them from damage and helps them to snug up nicely inside the tubes and to keep them from vibrating in the wind. A section of shrink tubing was also installed on the fishing rod and it is too big to fit inside the aluminum tubes. What this does exactly, is it ensures the rods are installed at exactly the right position when fitting them inside the tubes. The rods can't be installed too far inside the tubes or too far out. They will be inserted at the perfect spot everytime. This also demonstrates how the antenna will quickly break down and disassemble for storage.



    [​IMG]

    Prepare the poles to mount inside the tubes using a pipe cutter:

    [​IMG]



    [​IMG]
    [​IMG]

    I am also using some Dacron line on the hub itself to function as guy wires to help secure it in place.

    [​IMG]

    Antenna wires are mounted on the poles using UV resistant, mil spec. zip ties mounted to the spreaders and all antenna wires are routed in the following way.

    [​IMG]

    Hopefully this clarifies things for your project.
     
  9. NH7RO

    NH7RO Ham Member QRZ Page

    Thanks for all your photos and input on this, Charles. We have a lot of those tarp-frame hubs in use over here in Hawaii; just about every driveway has a tarp carport of some sort made with those hubs available at Ace Hardware. Good simple and inexpensive solution for 1" fiberglass.

    Ben, I appreciate your argument in favor of PVC and you make quite a lot of very good points---but like Charles pointed out, it will sag bigtime, IMO.
    Try it out though as we never really know for sure until we try, right?

    I have seen pix of a hexbeam (at least a 3-bander 10-15-20m) that was made with PVC and wooden dowels inside the first part out from the hub to stiffen it---apparently it worked fine---so what the heck, give it a try and if it doesn't work we won't snicker one bit. Experimentation is one of the great aspects of ham radio.

    Lots more to say today but am off to work for several hours now---will reply further when In get back home. Keep the thoughts and info coming, guys!

    73, Jeff
     
  10. AE7F

    AE7F Ham Member QRZ Page

    Yes Charles, thanks for your contributions. Great ideas. How sturdy is your setup? Great idea on the hub. I will price quote when I find some...
     
  11. AE7F

    AE7F Ham Member QRZ Page

    Oh, there will be some that might snicker! But that's OK. I will be checking out the schedule 80 conduit today for weight/rigidity.
    I found that the 1" pipe will fit into the 1.5" pipe but there is a 0.185" (4.669mm) gap, so that wouldn't make for a tight fit.... Everyone stocks 10ft sticks probably due to shipping cost of 20ft lengths.

    1" is 4.5lbs per 10ft and 1.5" is 5.25lbs per 10ft. A guy could always use schedule 40 and keep the grey color and UV resistance but I'm not sure yet if the rigidity to weight ratio is useful.
     
  12. AE7F

    AE7F Ham Member QRZ Page

    The 1" sch 80 does easily fit into the 1.5" sch 80 but there is too much slop to use the joint as is. I have pictures if anyone wants to see. You could build up the joint with vinyl tape or something but I think that wouldn't work very well.

    The 1.5" would probably suffice in a single 20ft length. Didn't seem overly heavy for a harsh WX QTH.

    I did however discover that 1" sch 80 fits nicely into 1.25" sch 40. I don't know if there would be any advantage to having a 1.25" portion of the spreader rather than just a full section of the 1" sch 80 connected via the existing bell ends. Anything smaller than 1" probably couldn't be considered for permanent installations and anything bigger than 1.25" is probably just too large.

    I have a picture of a 15ft spreader (consisting of the 1" sch 80 and 1.25" sch 40) and it looks good. Balanced in the middle, there is about 3" of sag on either side of the balance point. I could not test sag when the pipe was held off at the end but maybe 6". I really don't see why you could not simply guy it straight. Just guy in 3 or more spots along the spreader length.

    If you plan on using 1" ID spider joints, the above method will not work because the OD of the 1.25" sch 80 pipe won't fit into the spider. The above method requires a hub which can clamp to the spreaders, or a spider with a larger ID. The cubex spiders appear to accept 2" or 3" spreaders.

     
  13. KC8VWM

    KC8VWM Ham Member QRZ Page

    I can save you the time. The hub cost less than $10 bucks.


    The rods I am using are 4 x 12' long fiberglass fishing poles from Walmart. They cost 7 bucks each.

    My objective was to construct a very lightweight but structuarly strong antenna and indeed it is.

    Compare the weight of a 12 foot section of PVC pipe to a 12 foot fiberglass fishing pole in your hand and the fishing pole feels like no weight at all. The fishing pole remains rigid, (see photo) but PVC sags under its own weight. PVC is really not any more durable than fiberglass in this application. It is a LOT heavier though.


    How is it holding up? .. Quite excellent actually. Wind doesnt bother them at all. Probobly rated well over 100 mph. but I never drove my boat with the fishing rods fully extended at 100mph before but fiberglass fishing poles are well known to flex and recover quite nicely even with a salmon attached to them. I also catch a lot of DX with the wires attached to these fishing poles. :)

    The other issue with PVC besides weight is they warp out of shape in the sun over time. At 7 bucks a fiberglass pole PVC doesn't really save you much money anyways. You dont use the end section of fishing rod (the whippy section) just the solid sections are used for constructing your antenna. I didn't actually contruct a spiderbeam but rather a close relative to the spiderbeam instead.

    So you like pictures huh? lol :)

    IMAG0023.jpg

    IMAG0149.jpg

    IMAG0046.jpg
    IMAG0047.jpg

    DIAGRAM1_854x595.jpg

    IMAG0160.jpg

    IMAG0154.jpg
     
    Last edited: Jan 6, 2012
  14. AE7F

    AE7F Ham Member QRZ Page

    Charles, nice work. It doesn't even look like you guyed with extra rope. I can't see any continuation of the mast above your antenna. I like your thinking. What design is that, a 17-6m quad?

    Your design is certainly inexpensive enough to try. This past spring we had 75mph sustained winds for about 2 days. Ripped apart my dipole antenna. Haven't had a lot of snow or ice this year but we can get heavy snow and ice. If your design could be modified for guying above and below... hmm...

    The one criticism I saw concerning spiderbeams (besides the manual) was them coming down in harsh weather. Their fiberglass has a 2mm wall thickness.

    Your design fits the bill if it would hold up for me, but as I said, your spreaders and hub are pennies compared to what I've been looking at. I snow would do more to your antenna than wind. I'll bet the wind loading on your design is just tiny.
     
  15. KC8VWM

    KC8VWM Ham Member QRZ Page

    Wind loading is pretty much a non issue. The design is a Cobwebb Antenna (kinda like a VHF squalo horizontal loop but multiband and designed for use on the HF bands) It is completely resonate with a 1.1:1 SWR on 20,17,15,12 and 10m.

    **Instant on the fly band switching and no tuner or antenna rotor required. **

    I have also loaded it up using a tuner and it works on 30-40-60-80 and even 6m just fine.

    Way smaller than a hexbeam and yet the antenna elements are full sized on each band. This compact yet "full sized" multiband HF antenna is so small it even fits on the roof of this class C RV:

    IMAG0161.jpg


    It could be modified to include a support above it on the mast with dacron lines extending to the spreaders. Similarly you could add more rigidity and additional wall thickness support, by using expanding spray foam inside the fiberglass speaders. A can of expanding spray foam is pretty inexpensive and lightweight but it would add significant structural strength to the speaders if desired. In essence, the spreaders would become solid on the inside but remain lightweight if that makes sense.

    Quite frankly, I feel the epoxy resin fiberglass poles are pretty strong on their own though. After all, they are rated to hold at least a 20 pound fish on each one. :)
     
    Last edited: Jan 6, 2012
  16. NH7RO

    NH7RO Ham Member QRZ Page


    I really like your idea, Charles! I am also still considering a Cobwebb as my next antenna but am hoping to eventually have both a SB and Cobwebb---sort of like having both a Yagi and Squalo for 6M; it's always nice to have an omnidirectional antenna to instantly switch to on any band or for monitoring a DX calling frequency.

    For the time being I am hoping that I will be able to put up something as large as a SB when my xyl and I move to New Mexico three and a half months from now---won't know 'til we get there and settle into a place. If we are on the outskirts of town where big antennas won't cause a stir then a SB it is; otherwise maybe a hexbeam or Cobwebb will be my first and only choice.

    I've read all of your excellent posts about Cobwebbs and understand why you are so enthusiastic about them. If there was some way I could build a 5 or 6-band Moxon that would work well (probably not without making a ton of adjustments and compromises), I would. A single wire element version of the Cobwebb would be a very easy alternative and have the occasional benefit of being omnidirectional and thus never requiring rotation as you pointed out above.

    Even for hams who already have monster high-gain beams of any sort ought to have a Cobwebb as well if only for their omnidirectionality, IMO.

    Ben; One thing I wanted to point out in the PVC vs. fiberglass discussion is the important issue of wind and ice-loading. You mentioned in an earlier post that that would not be an issue at my location---which is true up until the time when I am no longer in KH6 (something I might not have made clear earlier). I am looking at all these options for a single 5-band beam precisely because I will soon be NH7RO/W5 on a permanent basis and want to have an antenna planned (and possibly even in hand) once we arrive in Albuquerque.

    So wind and snow loading is an equally important issue for me with this scenario in mind. I will be your not-too-distant neighbor to the SE from you in Utah come early spring. Albuquerque gets some severe snowstorms at times as well as strong winds in the spring. I used to live in Santa Fe (60 mi. north) and the winds there were hellatious at times!

    Nonetheless, I plan to try out a lightweight as possible spiderbeam (provided I am able to do so without major landlord/neighborhood aggro at my next rented QTH) and for that I plan to use the Max Gain Type 1L spreaders,
    thin wire, thin rope (Mac's), miniscule homebrew PVC insulators or equivalent, homebrew/Balun Designs 1:1 choke balun and one of those 1" tarp frame hubs Charles reminded us of (TNX agn!). That should keep my costs down to a couple/maybe three-hundred bucks tops, including a run of some new LMR400 feedline.

    I'll also try to work it so I can ground mount my trusty Yaesu DXA-800 rotator and use my 33' Portapole for the mast.

    Sound like a good plan? You bet! I'm excited already!

    More tomorrow or soon again, it's getting late here...

    73, Jeff
     
  17. AE7F

    AE7F Ham Member QRZ Page

    Charles,

    Throw us another breadcrumb on that hub. I guess I'm not using the right search terms. I haven't been able to find something similar to your hub. Or if the place you bought it from has an online web catalog I could look at, that would help.

    http://www.eham.net/reviews/detail/1671

    Looks like people like their cobwebbs. Cool. But these comments confuse me (http://www.g3tpw.co.uk/Page2CobWebbIntroduction.htm):
    The inherent losses and poor radiation efficiency of the mini-beams negates any so-called gain. Remember that if a beam has a gain of 4 dB over a dipole in free space, it will be DOWN on a dipole! It will also only “work” over a very narrow frequency range. A dipole or a CobWebb has a gain of about 5dB over a dipole in free space, (due to ground reflection) or 7dB over an isotropic radiator (7dBi) and will work equally well over the entire band.

    He says "if a beam has a gain of 4 db over a dipole...". He left off dBi or dBd. The calculations I have done (or seen) on log periodics and other various beams claim 3dBd or higher over a dipole.

    Then he says the "CobWebb has a gain of about 5dB over a dipole in free space" but it has been stated several times already that this is an omnidirectional design.

    ??
     
  18. AE7F

    AE7F Ham Member QRZ Page

  19. AE7F

    AE7F Ham Member QRZ Page

  20. NH7RO

    NH7RO Ham Member QRZ Page

    I plan to go to town later this afternoon and I'll price those hubs at Ace Hardware. As I recall, they usually have bins full of them!

    Speaking of hubs, what about those Rick Adams fabricated aluminum hubs? They look perfect; quite sturdy. Does he still make them for $40?

    73, Jeff
     
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