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MFJ magnetic rx only loop antenna

Discussion in 'Amplitude Modulation' started by N2DTS, Aug 8, 2019.

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  1. N2DTS

    N2DTS Ham Member QRZ Page

    I received my antenna today and stuck it up on an 8 foot mast stuck in the ground in my back yard close to the house (as a test).
    I have the 80 meter dipole, the zero 5 40 foot ground plane mounted on the roof, and now the loop antenna.
    The loop has an amplifier in the base fed power by an injector inside the house.
    On the broadcast band on up it seems to work VERY well.
    Lots less noise, lots less switching power supply noise, signals are down slightly sometimes but the noise level is WAY down.
    As it is, its a foot from the rain gutter in the back of the house, yet it seems to work great.
    As a loop, its bi directional, which is something else to experiment with, MFJ sells a cheap light duty rotor....

    Unlike most MFJ products, it seems well made!

    As an RX antenna, it needs no tuning to work on all bands which is great, its also very small, and seems to not need to be mounted high up!
  2. K5UJ

    K5UJ Ham Member QRZ Page

    That antenna is 1/2 the cost of the DX Engineering Pixel Loop. The physical construction seems to not be as robust but maybe it is okay. Let us know how it holds up. I have the Pixel loops because I got them before the MFJ hit the market. Mine are on rotators. There is a definite null, roughly 20 dB signal attenuation, when the loop is broadside to a point source. I have a pair that are feeding a phasing network. On 160 m. I was able to rotate them separately to be broadside to a plasma TV, then phase shift and null the residual noise. This was the ONLY thing that gave me peace on 160 m. against a plasma TV that used to be next door to me. The TV is gone and I don't use them as much now, but they're ready for winter operating with my inverted L and 75 m. 1/4 w. vertical when conditions improve.
  3. N2DTS

    N2DTS Ham Member QRZ Page

    So far, so good!
    It seems to be very well made, its a stiff metal loop mounted into what looks like an electrical box.

    I just have it pointed one way so far, and have found:
    On 80 meters signals can be as strong as other antenna's, and sometimes the signal strength is much lower, but noise is always lower giving a better signal to noise ratio.
    On higher bands, signals are often just as strong as the other antenna's but still with less noise.

    I do not think I have found a situation where the loop was worse then any other antenna in signal to noise.
    Same results if I just listen to the audio out of the receivers, the loop always delivers better sound, less background noise.
    My location seems to be fairly quiet at night, but even so the loop makes it even quieter.
    The G5RV antenna up at 45 feet is next best, then the zero 5 40 foot roof mounted ground plane.
    Sometimes signals are much stronger on the zero 5, but so is the background noise. Maybe a better TX antenna.

    If you did not have space, that seems like a good combo, the zero 5 for TX and the loop for RX 40 meters and up.

    I don't know the effect of height above ground with the loop, I first had it up 12 feet and it worked fine, now its up 16 feet and I don't think its any different.
    You could put it in the attic and it would likely work fine.
  4. K5UJ

    K5UJ Ham Member QRZ Page

    Up to a point height doesn't seem to matter. They work as well at 8 feet as they do at 20 feet. What's important is that they aren't near a structure. In some cases they can be indoors but not always. It depends on the building. Don K4KYV has a loop inside his ham shack. No problem because the shack is a wood building. My house and garage are sided with aluminum. My antennas have to be outside and above the sides of the house and garage. The same would be true for stucco as stucco uses a wire mesh to hold the mortar material in place. What do you use for feedline? I'm told that quad shield RG6 is best. I bought a 500' roll of comscope duo shield RG6 at a hamfest before I knew that so I'm using it anyway.
  5. N2DTS

    N2DTS Ham Member QRZ Page

    Just using RG8m to feed the loop, its only about 15 feet of it....
    The loop is close to the rain gutters.....I need to find a good location for it, its right below the G5RV antenna....
  6. KL7AJ

    KL7AJ Ham Member QRZ Page

    I think MFJ has been upping their game a bit lately. They've ALWAYS had great engineering....only the QA has been a bit under par...and I think they're fixing that.
    K6CLS likes this.
  7. N2DTS

    N2DTS Ham Member QRZ Page

    I would not count on it, but I opened up the amp in the loop and it looks well made.
    The loop itself is a sturdy thing for a cheap loop....

    I have not had a lot of mfj stuff, but I would open it up and check the solder and for tight screws before using any of it.

    Funny story:
    Around 1980 I went to a hamfest in Pennsauken one of the first ones I ever went to, and bought an MFJ antenna tuna, versa tuna 2 or something,
    just because I felt like buying something.
    Went home and tried it out and found it shorted inside.
    Took the cover off and found the coil against the lid.
    I fixed that and got on CW and worked N2DXM on 40 meters I think.
    I proceeded to rag chew about my duff tuna and Steve thought I was his friend who went to the same hamfest with him.
    Steve, (N2DXM) bought the same tuna, and had the same problem, then got on the same band on CW and contacted me.

    He would not believe I was not his friend.
    I met up with him later that night and we became friends.

    What are the chances?

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