Loops?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N9RMA, Nov 13, 2017.

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  1. N9RMA

    N9RMA Ham Member QRZ Page

    Reading lots of info on mag loop antennas. Thinking about making one for 10 thru 40 for the digi modes. I have a large air gap cap that will work for tuning. No QRO involved /30 watts max. This way my other antennas will be free for SSB Etc. Looking for any and all comments either YEA or NEA. Thanks Bob N9RMA
     
  2. NH7RO

    NH7RO Ham Member QRZ Page

    I vote YEA.

    You might want to join or take a look at two Yahoo Groups; VE3UK's "The Mag Loop Group" and K8NDS's "The Helically Loaded Fractional Wave Antenna Group"---lots of good info and examples to emulate there. (link to Rich's site: https://groups.yahoo.com/neo/groups/Helically_Loaded_Mag_Loop/info )

    I've built several small electromagnetic loops capable of QRO and have enjoyed working dx from my antenna restricted location in recent years.
    I'm still planning more experiments in the future, too. Building STLs can become addicting as eating corn chips!

    While most people still call them "magnetic loops" that is really a misnomer---while the radiation in the near field is mostly magnetic the far field is mostly electrical as with every other kind of antenna ever made. Hence i refer to them as small transmitting loops, electromagnetic loops or fractional wave antennas. Fascinating skyhooks/skyloops or whatever one calls them!

    While a QRP STL can tune 10-40M it is generally better to aim for only one octave range for best performance---but if you're only going to be doing digital stuff you can slide by with an inefficient and lossy loop such as most of those commercially available nowadays. Btw, the MFJ-1786 covers 10-40 and generally receives high marks from most of its users in case you end up buying rather than building.

    There's also a new STL being made by an outfit called Professional Communications that looks like a darn good value considering its size and construction (under $300), too.

    In my opinion it is often better to build one's own from scratch, though. I gained a lot of inspiration for my first builds from seeing what others had done on VE3UK's and K8NDS's sites. Look through the many photos there and see what can be done. One fellow in Germany made his loop out of an old alloy bicycle rim! I have several pix of my loops midway down my long QRZ page if you're interested.

    Btw, if you can get your hands on a 10-foot scrap of solid shield Heliax you can do well with that for your radiating element (much less lossy than coax braid) and a decent split stator or butterfly capacitor will fill the bill nicely.

    Have fun and enjoy the discovery of what such "magic loops" have to offer!

    One very important link to check out before I go here:

    https://www.nonstopsystems.com/radio/pdf-ant/article-antenna-mag-loop-2.pdf
    (STL guru Leigh Turner's excellent 32-page read and a must for anyone wanting to learn more about STLs)

    73,

    Jeff
     
    KX4O likes this.
  3. KO6WB

    KO6WB Premium Subscriber QRZ Page

    It's going to be difficult to find, or make, an air variable capacitor that will enable 40-10 coverage.
    The MFJ-1786 covers 30-10 and the MFJ-1788 covers 40-15. This is because of the air variable capacitors tuning range. This capacitor is the only difference between the 1786 and the 1788.
    I used a vacuum variable capacitor, which had the wider tuning capacity, when I built my STL. It covered from below the 40 meter band to just above the 10 meter band. It's shown on my QRZ lookup page.
    The efficiency on 40 is not all that great but I had no problems checking into the noontime net here on the west coast. I even worked some DX when the conditions were right. Sometimes you just have to time it right, kinda like operating QRP.
    With the VVC I was able to operate with 100 watts. Could handle more if I upped the voltage rating of the VVC.
    On other STLs I am able to operate at greater than 500 watts. Again, this is due to the higher rating of the VVC.

    Hope this helps
    73
    Gary
     
    NH7RO likes this.
  4. N9RMA

    N9RMA Ham Member QRZ Page

    Thanks for the replies. That is the great thing about ham radio. It is fun to try things and if it doesn;t work try again. Will carry on with the fire department on standby. Bob N9RMA
     
    NH7RO likes this.
  5. KQ0J

    KQ0J Ham Member QRZ Page

    Compromise antennas are great for compromise situations, and only compromise situations.
     

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