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Ham Radio Adventures 19: Tuning magnetic loop antennas by ear

Ham Radio Adventures 19: Tuning magnetic loop antennas by ear

28 comments on “Ham Radio Adventures 19: Tuning magnetic loop antennas by ear

  1. The difficulty with magnetic loop antennas is that they are NOT resonate at 50 ohms – and I suspect that the resonance is different for each antenna design (because it is sensitive to the coupling loop geometry). When you use a VNA to look at a magloop you will see that peak noise IS actually centered in the antenna passband. Unfortunately, by detuning the loop to match the transmitter's 50 ohms we reduce loop performance. I think a better solution will be to use an antenna tuner in conjunction with the magloop. I know this is not conventional wisdom, but am convinced that it will produce the highest performance – especially at lower frequencies.

  2. I really enjoy your videos. Tnx again Richard! I did nearly the same test a while ago and came to the same conclusion. An antenna analyzer is a must have on portable operations. Right now I am using a Rigexpert, but thats to bulky. I am looking for something smaller, eg. RigExpert Stick or the Youkits you are using. 73 Stephan, DF6PA

  3. Good demo Richard. I have a h/b mag loop indoors that I sometimes rx on and you are right re the sharp tuning vs actual precise resonance hence SWR meter preferred. The relatively close proximity of your body probably also has an effect as you lean over to turn the tuning capacitor and then move away so defo better to have a small analyser or an in-line SWR meter at operating position to avoid cooking something. Cheers, Nick

  4. Because I was taught to tune by ear I never bothered with meter but I now have nanoVNA so easy to take with me in future.

  5. Hi Richard, I had a borrowed Alex Loop on a SOTA , a windy SOTA at that and found it practically impossible to tune it by ear due to the background wind noise using ear buds. I see AlexLoop are now marketing a clamp on gizmo to aid tuning

  6. I wonder if the transceiver's input impedance, when in receive mode, is actually 50 ohms. There's no good reason why it would have to be designed that way. If it is something else and you tune the loop for maximum noise, then what you are doing is arranging for best match to whatever the transceiver's input impedance (as reflected to the loop end of the coax) really is.

    To get around this I suggest putting a 50 ohm T-pad, perhaps with 10 or 20 dB loss, between the loop and the transceiver while tuning for maximum received noise. Then the loops will pretty well see 50 ohms and when you tune for maximum received noise and then remove the T-pad and measure the SWR I'll bet it will be pretty close to 50 ohms.

    David VE7EZM and AF7BZ

  7. Richard, thanks for your video. I use a Chameleon F-Loop and have some difficulty with high SWR especially with my FT-817, would it be possible to just tune for lowest SWR using an antenna analyzer then hooking up the feedline back to the radio, OR was there high SWR no matter what you tried? thanks for any feedback 73

  8. It is difficult also with automatic tuning box for the lowest swr you need a swr meter, you let us see it in de video tnx

  9. Thanks for another interesting video Richard. I was a little surprised at the results. I only have experience of using a mag loop that I home brewed. With this, I was surprised how close to 1:1 VSWR I could manage just tuning by ear. Though, I do usually check it using the SWR indicator on my FT-817. I have been meaning to make a little indicator for my loop – short pickup wire, diode rectifier and smoothing capacitor plus an LED. The idea being to tune for maximum LED brightness on TX. This would allow the loop to be used without an SWR meter or VNA and adds hardly any bulk/weight to the set up.

  10. Whoa! I sold my loop last year. Paid big bucks for it and it was sold saying "no tuner needed" I could never raise anyone with 5 watts. Now i know why..

  11. Richard, I am not a big fan of these antennas. I would rather buy one of your antenna kits(more compact, lighter and easier to carry) with a small portable mast and a qrp rig with an antenna tuner. Inverted Vs are bound to work better than a loop like this. Rich KB5EDR

  12. I’ve been very disappointed with my Loop and Yaesu FT-817ND. So hard to get a good match, and rig shows a hi SWR.

  13. I have only ever done it on a homebrew loop, on 20m (which it was built for) and with a station i was about to try and work; so their audio was fairly constant through the tune. With those constraining variables; 10w to Italy SSB with no reported issues on his side.
    The loop worked on 15m down to 40m, and using digi modes, outwith 20m and 17m, i needed the radio swr meter to get get a match. Was way to sharp to do by ear.

  14. Nice idea, good demo. I think it is very difficult to find a noise peak by ear. Even below the AGC threshold of the radio, the ear has a quasi logarithmic response, you can’t really identify by ear a peak that is only 2 to 3db in actual amplitude so peaking the noise is quite inaccurate. I wonder if using a sound level app on a phone would produce a more accurate peak position. We all usually have a phone with us. Sound level display needs to be in a non-logarithmic mode. (VK1DA)

  15. Good information. AND I have three different antenna analyzers and find (loke you) that the YouKits one the easiest and fastest one to use for antenna tuning. It doesn’t give all the parameters that the other ones do but it tells SWR and impedance. Just what we need to tune a loop or other antenna in the field. Considering the poor results of tuning by ear it is still very interesting to see what we can do just by putting out a signal with whatever rig and antenna we have. Get on the air and make some noise.

    Dave K8WPE

  16. What stand are you using under the mag loop? Is there an adapter between the base of the mag loop and the stand? Thanks!

  17. I tune for max noise on my doublet and screwdriver. Then I check it with a meter and its real close. But I think you need an swr meter of some kind.

  18. I was so surprised by your results. Most of my rigs including some homebrew have built in swr indicators and I do minor tweaks after audio tuning. I do not think I have ever been that far away from tuned. As a side note we must not be obsessed by SWR a dummy load has a perfect SWR ; )

  19. I wonder if looking at the brightness of a LED could be discerned by the eye any better than the audio by ear.

  20. Richard on the 40m test did you try and get the SWR down by using the analyser ? it could be that the SWR you show was the best you could achieve even with the analyser – Dave RCQ

  21. Your video- once again, very well done, Robert. Thank you.
    I have also made some tryings for tuning mag loops by ear and came to the same conclusion that this is not sufficient for an exact match. So I remembered the tuning by means of the good old glow lamp. One of the two wires is soldered to the tuning capacitor (rotor), the other one remains unconnected. By closely observing the increasing light intensity while tuning the loop`s capacitor, the resonance point can be adjusted quite precisely.

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