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Jetstream JTV680

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W8HVI, Nov 1, 2012.

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  1. W8HVI

    W8HVI Ham Member QRZ Page

    I just purchased this for my cabin in Northern Michigan. I am planning to mount it on a tripod on a metal roof. Is this a good idea or a bad one. Any comments about the performance of the antenna?
    thanks
    tom
    W8HVI
     
  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Information is rather sparse and they really do not justify their "no radials required" with any reasonable explanation. Having the antenna in close proximity to a metal roof probably will help it. I'm certain it isn't going to hurt it.
    Lots of folks have various antennas they believe to be the best thing ever. There is no comparison antenna up at the time when they say the newer antenna is doing great and wonderful things. No reference means they're just guessing and most of the performance is actually good propagation where just about anything will do if it can put out a bit of RF. There are no miracle or magic antennas that blow away other simpler antennas that cost far less. What you have is a length of aluminum tubing 23 feet long with a type of matching network to make it look like it's doing good. Too many amateurs are lead to believe a low SWR means the antenna is doing great. It doesn't mean that at all. What a low SWR means is the impedance of the transmitter is matched to the impedance of the load. If that load happens to be part of an antenna then there will be some radiation from it. Even a dummy load has a certain amount of radiation. A low SWR means there is the best transfer of energy to the load. If the load absorbs the power and converts it to heat then that power isn't doing you any good. This is what is happening with the JTV680. It will put out a signal and it is definitely better than no antenna at all but if you could make other choices then you should do that.
    Basic antennas that do well are detailed in this posting; http://arrl-ohio.org/convention-2012/Wire%20Antenna%20Basics_ARRL_Ohio_8-11-12.pdf. It's only 84 pages long so it doesn't dwell on things much and generally covers what works (except the end about the J-Pole).
    Hope this helps
    73
    Gary
     
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    On a tripod over a metal roof should work fine; however be aware this is a Chinese knock-off of a Comet CHA-250B:

    http://www.cometantenna.com/products.php?CatID=1&famID=5&childID=6

    Jetstream isn't a manufacturer, they're an importer/distributor of products from China. The original Comet CHA-250B is made in Japan and the Jetstream is a "knock-off" of that. I'd be mostly concerned about build quality and also whether the tripod is strong enough to support a 24' long vertical antenna in a strong wind, as the forces on the base and mount can be amazing.
     
  4. W8HVI

    W8HVI Ham Member QRZ Page

    Appreciate the response with the additional info
    73
    tom
     
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