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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!
     
    KK4NSF likes this.
  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.
     
    KK4NSF likes this.
  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.
     
    KK4NSF likes this.
  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.
     
    KK4NSF, AC0OB and K6CLS like 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?
     
  8. N2DTS

    N2DTS Ham Member QRZ Page

    I was working Joe last night (in Georgia) and signals were up and down and weak.
    Switching between the three 40 meter antenna's was very interesting, sometimes his signal was much stronger on one antenna over the others and
    it kept moving around.
    We both tried transmitting on the vertical antennas and that always resulted in a lower signal at the other end, but sometimes the signal was much stronger using it on RX.
    Sometimes the loop was a lot stronger, sometimes the dipole.
    Switching the antennas kept the copy as he would be gone on the others.
    Its quite amazing the difference at times.
     
  9. N2DTS

    N2DTS Ham Member QRZ Page

    I picked up a W6LVP loop antenna to compare with the MFJ loop.
    I can not see a lot of difference between them.
    The MFJ is a sturdy piece, and its stuck being large.
    The W6LVP is made from coax and can be made small for portable use, plus it uses BNC connectors so you could make
    different size loops.
    A bigger loop would work better on 80....

    I also picked up a $45.00 loop made by funtronics sold by elekitsorparts.com.
    This is a very small package with a thin stainless loop that is designed to work into something like an sdr-play rsp with the bias T.
    It does have a power injector that plugs into a usb port or charger or battery, and it also comes with a long, thin coax cable with
    little SMA connectors on it.
    It also seems to work ok from limited hand held testing.

    With the MFJ you are sort of stuck with the loop you get, a big thick conduit type setup.
    The W6LVP just needs a bigger piece of coax or whatever, and supports.
    The funtronics would be very easy to make into whatever loop size and type you want.

    Only the MFJ is un potted.
    Its not really water proof but more like any water would just drain out the bottom.
    You could water proof it without much trouble....

    I think it will be sort of interesting to have a TX antenna directly connected to the transmitter and then use an RX antenna.
    No T/R relay, and the loops are broad band (all band) so no switching there.
    For 80 and 40 and maybe 20, a 6 foot loop might work much better.
    The current size is about 3.5 feet across...

    They do not have to be high, they are not very big, they cut a lot of the noise, they are not expensive, they are broad band, two at right angles might be very useful to cut qrm, and/or a rotor.
     
  10. AC0OB

    AC0OB Subscriber QRZ Page

    I assume your loop is mounted with the open area pointing horizontally?

    Is there any way to mount it with the loop looking vertical to see if there are any differences/improvements?


    Pheel
     

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