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2M/70CM Tape Measure Beam

Discussion in 'Satellite and Space Communications' started by K6LCS, Jan 8, 2012.

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  1. K6LCS

    K6LCS Premium Subscriber QRZ Page

    >> ... I never understood the allure of tape measure beams. They're not easier to build and certainly not more efficient than other designs, and if you're not constantly adjusting element lengths I see no reason for them to be calibrated ...

    PLEASE do not take the true FUN out of ham radio!!! (grin) Building a tape measure beam (well, at least the ones that I post on my Web site) are VERY fun to build (where "fun" is defined as "easy to build, not expensive at all, AND gets me into the world of high gain for under twenty bucks US").

    "Constantly adjusting element lengths?" I haven't adjusted a single element on mine - using the projects I have posted. "Calibration ... " Huh? I wouldn't DREAM of whipping out my $500 antenna analyzer to fine tune what works GREAT for me already ...

    Might be a case of an "engineer" looking at the drawings, and not being pleased ... as opposed to those of us who have used these in the "real world," and know how FUN they are!

    I discuss bumping into an engineer who "experienced" an Arrow sat antenna: “Arrows are all engineered wrong - they cannot possibly work.” My discussion is mid-way down the page at ...

    http://www.work-sat.com/Work-Sat/My_Gear.html

    No, I would not attempt nor recommend mounting a tape measure beam on my vehicle and working birds at 75MPH. But if I wanted to experience true 6-9db gain on 2M/440 with an HT with an antenna system that drew inquires from acquaintances (and strangers), then I'll whip out my tape measure beam any ole day!

    Clint K6LCS
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Clint, I never implied they need to be adjusted at all. What I implied was "why do you need calibrations (provided by a tape measure) if you're not adjusting anything?"

    The quad I referenced can be built for about $10 using wire, a piece of dowel or bamboo for a boom, and spreaders made from "free" paint stirrers from Home Depot, which is exactly how most of them were built.:eek:

    One advantage of the design is perfect balance at the feedpoint, negating the need for any sort of matching device or balun. A yagi (tape measure or otherwise) without a balun is guaranteed to have an imbalance when fed with coax.

    I think anything we build is fun, I just try for more optimal designs if I'm going to take time to build something.
     
  3. W5PFG

    W5PFG Premium Subscriber QRZ Page

    I like your style.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    BTW regarding inquiries from strangers/onlookers, when I have the quad and everything else on the roof of my van, it gets a lot of inquiries. If I have time, I explain about ham radio; if I don't I just say, "We're making a movie," and get rolling.

    Believe it or not, that's an acceptable explanation for most, if you're in a hurry.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I can't see using silly materials when better ones are available, cheaper.

    Tape measures are usually painted steel. When you scrape the paint off to make electrical contact, it rusts. Exposed to the elements outdoors, even the painted areas rust unless you have stainless steel tape measures, which aren't the cheap ones.

    Rust is a terrible conductor.
     
  6. W5PFG

    W5PFG Premium Subscriber QRZ Page

    Nice one. I once had an older fellow, quite belligerent, try to interrupt me while working a satellite pass from a VERY remote West Texas location. He kept asking off-the-wall questions so I politely told him "I'd be done in about ten minutes and explain fully afterwards." Finally, I just told him "I'm trying to contact the mother ship." and he abruptly left.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'm in southern CA and based in L.A. close to Hollywood, so most people are used to seeing weird stuff related to making movies. Vans with rooftop dish antennas and millions of cables going in and out are really routine, so I just use that excuse if I'm in a hurry. But if I have time, I'll explain about ham radio and usually carry some of the ARRL pamphlets with me to hand out, just like we would at Field Day when people stop by. Hey, they're free!
     
  8. K6LCS

    K6LCS Premium Subscriber QRZ Page

    >> ... tape measures are usually painted steel ... even the painted areas rust ...

    >> ... a yagi (tape measure or otherwise) without a balun is guaranteed to have an imbalance when fed with coax.

    Man, we seem to be butting heads here - one of us is trying to make up all sorts of reasons NOT to build a tape measure beam, another has shown it working excellently to many audiences the past few years.

    "Rust" is a non-issue with my five-year-old tape measure beam. Never put a balun on mine, either, as I feed my Ht with coax. But it works. I have seen scores of these in the field working just fine - with no baluns and no rust anywhere.

    And so it goes ...

    Clint K6LCS
     
  9. W5PFG

    W5PFG Premium Subscriber QRZ Page

    The impedance at the feed point of a Yagi is typically not 50 ohms. If you connect a piece of 50 ohm coax, you will have an imbalance resulting in higher SWR and subsequently a poor transfer of RF from your radio to the antenna. Some tape measure beam designs do employ a match -- that's great. Others use a split driven element at an attempt to have a balanced feed point. Many new hams looking to build their first satellite antennas should take a little more care to understand that pushing 5 watts into an untested beam *may* result in damage to their handheld or even worse. Fortunately most new manufacturer handhelds are fairly tough and will not fry their finals into a poorly constructed antenna.

    The fact of the matter is, many of these experimental antennas do work fine for the average Joe. You can save a few bucks over a commercial Arrow or Elk with the 2M/70CM in Clint's original post or any of the ones subsequently listed. Do they work? Yes. Are some more efficient than others? Most definitely. This is why I would classify a tape measure beam as a very "introductory" application or project, not a daily driver. Of course, it would work for that use, but not MY recommendation.
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Glad they're working for you. Not trying to "butt heads" in any way, just pointing out there are many ways to skin a cat, and when one way works better and costs no more, that's the way I'll usually go.

    I don't even work the FM sats, as the first few times I tried it was way too easy. Making a contact first time out with very little effort isn't what the hobby is about, for me. But, different strokes, for sure.

    I've worked ham sats since October 1972 when the first operational transponder on OSCAR-VI worked. That was mode (A), 145.9 up/29.45 down, and I have the certificate from AMSAT for completing contacts on its first operational pass. Everyone who used it that day got the certificate -- I think there were about 350 of us or so. It was CW-SSB only. I used a homebrew 2m transverter connected to my Heath Marauder transmitter, and an NC-303 receiver, with an 8L yagi on 145 and a 3L yagi on 29, both on the same el/az rotators on a roof tower at my parents' house.

    Now, to me, that was the fun part.:eek:
     
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