Magnetic Loop Antenna Indoors Apartment

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KT4JX, Feb 11, 2018.

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  1. KT4JX

    KT4JX Ham Member QRZ Page

    Will these antennas work at all inside a bedroom or living room? There's a brand called Alpha Antenna that has great reviews, but they're expensive. Are their any cheaper brands? And, do these have to be grounded and is it safe to transmit 100 watts indoors?
  2. KK5JY

    KK5JY Ham Member QRZ Page

    Don't buy an STL. Build it. It is almost impossible for a commercial STL to compete with the efficiency you can get from a hand-built antenna. A hand-built antenna will be much cheaper, too. :)

    See the comment I posted here earlier this evening. All of those antennas can handle 100W safely, and all but one can do 500W.
    K3RW and AK5B like this.
  3. W4KJG

    W4KJG Subscriber QRZ Page

    Take a look at this thread from two years ago:

    Here is a little more detailed info about this simple antenna.

    Then take a look at PD7MAA's website for additional antenna ideas.

    He has other articles, and I can't find the one I used to build the one I used. I put one of these up on a wall in our snow bird home using #12 wire and corkboard tacks. Running about 20 watts on 20 meters I made a number of JT65 contacts with it. I let it run on my receiver for a couple of days and it logged a lot of JT65/JT9 signals from Europe, North and South America, and a few from Austrailia.

    It is cheap and easy and can be used as a temporary antenna.

    Good luck,
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    How well "any" antenna works indoors is pretty dependent upon the building's construction.

    But STLs can work well even very close to the ground, which is a big plus. I've used my MFJ "Super Hi-Q Loop" which covers 40-15m and is only 36" in diameter hanging from a low tree limb at campsites, where it was maybe 5' above ground, and it did fine -- but of course, it was also "outdoors." Same loop "indoors" inside my stucco-sided home doesn't do nearly as well.

    AK5B likes this.
  5. KE9RJM

    KE9RJM Ham Member QRZ Page

    I tried a mag loop inside my single story house, I could hear just fine but had no luck transmitting. returned it, took the hit on shipping and am still looking for a solution.
  6. AF7ON

    AF7ON Ham Member QRZ Page

    I also tested an MFJ Hi-Q loop indoors and found it worked decently, especially when located next to my glass patio doors. It is safe enough a foot or two away from the operator. It works better outdoors, though.

    One issue you have with all indoor (and attic) antennas is coupling to wiring and plumbing that can severely compromise antenna performance.

    WB5YUZ likes this.
  7. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    It's not safe to transmit 100 watts with an Alpha Loop, period. They are limited to 15 Watts continuous or 30 W PEP.

    If you get a tuner from the MFJ 935 family, which is basically the "tuner" part of the STL, you can easily build a nice efficient loop yourself out of flexible copper tubing or similar and have an outfit that will run 100 W.

    As per AF7ON above, whatever kind of loop you get, try setting it up outdoors whenever convenient. You can generally run a very long patch cord to them, as the input presents a very good match to 50 ohms.

    AK5B likes this.
  8. AK5B

    AK5B Ham Member QRZ Page

    As gung ho as I am about properly constructed STLs I would never even consider using one indoors unless it was a true emergency.

    All that house wiring, ducting, large metal appliances and stucco screening quickly puts a damper on one's chances for success. Coupling, coupling and more coupling. Get that loop outside, even if only a few feet or so and temporarily while QRV.

    Since building one from scratch is really the way to go with these I would also shy away from 98% of the commercial offerings out there, too. The only exceptions would be the seriously expensive Ciro Mazzoni Loops made out of welded aluminum or perhaps an MFJ-1786 mounted somewhere outdoors in the clear (or better yet; a MFJ-935B and a set of half inch soft copper loops for each band of operation). None of these need to be elevated much, either---one of the greatest things about STLs.

    I have regularly worked dx on 20-17-15 meters with my high-band loop only 44" above ground in my back yard. You can, too!

    There again, if you really want and expect good performance out of an STL it practically requires DIY and using the best ingredients. There is no way around the detrimental ohmic losses unless a continuous radiating element and a vacuum variable cap are employed. Other methods will work at greatly reduced efficiency thereafter. (Hence the crowd of naysayers that are quick to dub all STLs as "dummy loads" which I must reiterate is about right if one is referring to the majority of commercial offerings.)


    K3RW and KC8VWM like this.
  9. K6CLS

    K6CLS Ham Member QRZ Page


    I tried connecting to the chicken wire in the stucco, that didn't work either.
  10. KK5JY

    KK5JY Ham Member QRZ Page

    Like I said, never buy an STL... the commercial versions (at least the ones cheap enough for most hams to buy) make too many compromises to be efficient.
    AK5B likes this.

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