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Thread: I need stealth, low noise, and gain in the same antenna

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  1. #21
    Join Date
    Feb 2004
    Location
    Bakersfield, CA
    Posts
    4,604

    Default

    KD7VEA
    I need stealth, low noise, and gain in the same antenna
    .
    Pick two. You just can't have everything in one antenna.
    Now, in regards to a magnetic loop on the bands 20-10 meters it can be effective in a small size. The circumference is part of obtaining the best efficiency. Larger is better but there is a limitation on that. Make it too large and you lose the upper bands, too small and you will have no signal on the lower bands. In application you can make a very small loop work any band you want. I do have a magnetic loop and it is 40 feet in circumference made out of 1" copper pipe. This is not the ideal size for the lower bands but it is economical. Have you priced copper pipe? The loop is supposed to be using 2" or better however the efficiency doesn't suffer that much with a smaller diameter conductor. It is about 1db lower that the 2" pipe but it is 75% cheaper to build. There are numerous articles on the internet about this type of antenna. There are few commerical vendors and it is definately better to build it yourself. The commerical ones are not cheap and you can only work at the maximum 100W. Mine can do 500W and tunes 80/75, 60 and 40 meters. It is 6 feet off the ground with the top up at 16 feet. It does work.
    Hope this helps
    73
    Gary

  2. #22
    Join Date
    Feb 2003
    Location
    Wonderful WYOMING, Accept no substitutes.
    Posts
    3,596

    Default

    Utah is a tough nut to crack. I am up in Wyoming and know what you are dealing with. Most of the DX you mention is almost exactly north over the pole. We have a extremely rough path to Yemen for example (since it is the DX going on now).

    You have gotten some great advice from the folks here. I will tell you, to work a lot of DX from this part of the country, a beam REALLY REALLY helps. I run a large beam at a large height and even if I cannot always work the DX due to a pileup, I can generally hear them.

    Unfortunately, we are several thousand miles from the nearest DX (except Canada) and really pay the price. But think about it another way, we do have a beneift that others do not. We have an equally sucky path to ALL DX.

    For example, East coast were really struggling to work T32C. West coast is struggling for 7O6T. Here in the rockies, we struggle for it all!!!!

    Go bigger and higher and you will start getting a lot more DX. I now it is hard, but I seems to be the requirement from this part of the U.S.

    Brad
    "Life is just like ridin' broncs, its a battle". Chris ledoux

    Long live Steamboat

  3. #23
    Join Date
    Apr 2002
    Location
    Rochester, MN
    Posts
    19,634

    Default

    There are a number of rotary dipoles to choose from. There are also some small 2 element tribanders that would help a lot on the higher bands.
    Moseley has to different ones to choose from.

    With the rotary dipole, I'm not sure if I'd rather have 10-15 and 20 or WARC bands right now. But 10-15-20 is where you will find the contests when they roll around - a good time to work DX.
    EchoLink, IRLP, Allstar and DSTAR linking - adding interest to repeaters worldwide 24X7

  4. #24
    Join Date
    May 2002
    Location
    Rockport, TX
    Posts
    1,187

    Default I second the cobweb nomination

    Quote Originally Posted by M0GVZ View Post
    Google the G3TPW Cobweb antenna. Five fullsize dipoles for 20-10m in an 8ft square. Almost omnidirectional with a slight 3dB variation between the ends and sides which gives a slightly oval pattern. At 30ft up it'll do quite well.

    Quite easy to homebrew - look at the G3TXQ variant which is easier to tune though.
    A cobweb might surprise you in terms of size and performance. A Moxon rectangle is another good choice if you want decent performance for a single band out of a stealthy and compact design that is easy to construct.

    Either will give you FB results at 30 feet, too.

    73, Jeff

  5. #25

    Default

    Thanks everyone, I am getting a ton of good info. The plan is to put up the tower, and at least a tr iband beam once I get into a different house, it just cant happen here. I dont need to be too stealthy I guess, it just has to fit in the yard(realistically). I think I may try to build a small 2 element beam or a cobweb. I like that I can get all 5 bands (10-20) in on antenna. I have thought about the magnetic loops, but I have never got a good straight answer on the noise level. Some people say that they cut the noise level down, and others say it makes no difference.
    KD7VEA
    www.kd7vea.com

  6. #26
    Join Date
    Apr 2001
    Location
    Shropshire. England.
    Posts
    17,212

    Default

    No such thing as a stealth high gain antenna. I have the same problem with a Cushcraft vertical, I can't hear the DX either ! Most of the problem are the poor propagation conditions. There was a time in the late 1980's when you could make contacts all over the world with a poor antenna and a "piece of wet string" Those days have gone. The biggest killer is QSB, I can wait for 5 minutes for a contact to close with a station and give a call but they fade away ! just like that !gone ! I have a list of all all the station I heard and to look for when they re appear, the list is getting longer.

    I have a 90 ft dipole with dropped ends at 27 ft and with 20 watts PSK had a contact on 30 metres with Melbourne Australia. 30 metres has been useless now for 12 months, there's even fading on stations in France 350 miles away. Propagation is the answer

  7. #27
    Join Date
    Feb 2004
    Location
    Bakersfield, CA
    Posts
    4,604

    Default

    On the near field stuff a magnetic loop is quieter. That's the good news, and the bad news is, there isn't much of the noise that's in the near field. In comparing a short vertical I have to the magnetic loop the loop is quieter by about an S unit but the receive signal is up a lot. This make the important SNR much better. The magnetic loop antenna can work well at low height but there is an optimum height for them and if you can meet that then you will have some very good low angle radiation.
    The loop is tunable so it doesn't require an antenna tuner. The loop is a high Q antenna which means it is very narrow in bandwidth. On the lower bands the Q is so high and the BW is so small that even changing sidebands you would have to retune. It takes just a second or so to do that. Excursions from band to band is like rotating a beam to a new heading, it takes time. A lot of the loop users have their loop rotatable since it has deep nulls to the sides. This comes in handy when you want to null out QRN or QRM or to get the antenna aligned to work in it's favored direction. The nulls only show up if you have the loop at the proper height and on the upper bands, it isn't that high.
    I have had some success with the magnetic loop and for those with restricted capabilities it can do some really good things. Does it beat a 1/2 wave dipole? Not quite except if you get it up higher then it has better low angle radiation then the dipole. In other angles it can be very close to a dipoles pattern and gain.
    I could tell you that the difference between the short vertical and the loop is 15 to 20 db but the question then becomes, is it because the loop is that much better or was it that the vertcal was that bad? None the less, it is an improvement and that was the goal.
    Good luck
    73
    Gary

  8. #28
    Join Date
    Jan 2006
    Location
    Salinas CA
    Posts
    49

    Default

    Try the following: An off-center fed dipole with a 4:1 current balun at the feedpoint. I use a Balun Designs 4114 ocfd balun which cost me only about 80 dollars. Mine is 90 feet of wire one direction with 45 in the opposite, a 30 foot metal mast in the middle (the 4114 is designed to be used near metal objects), but for a smaller space 45 and 22.5 feet will give 40 and the even harmonics (10-20) and will tune to 17 and 12 (but not 30). I get 80-6 and use it without a tuner except for 75, 17, 15, 12. There is gain (see http://hamwaves.com/cl-ocfd/patterns.html) but resonance is more important than gain. Remember that the gain of an antenna is offset by losses in the system, including the feedline and any tuning that needs to be done. If the mismatch in the system is allowing only 80 watts to get out untuned, that is still the amount that will be put out by the tuned antenna. My wire is 13 gauge poly stealth wire, HRO Item # PS-13-100.
    Last edited by KG6ZAN; 05-07-2012 at 05:53 AM.

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