Magnetic Loop help/info needed

Discussion in 'Community Help Center' started by ZL3BL, Dec 14, 2018.

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  1. ZL3BL

    ZL3BL Ham Member QRZ Page

    I've built an rx only magnetic loop feeding the rig via a small pre-amp. In use, it is as sensitive as a loop of 60 metres circumference at 3 m/10ft height. At this time, there is no coupling loop, as intent it to mount it externally at 5 metres. The pre-amp and the lack of a coupling loop means the antenna isn't tuned.

    Is there anything to be gained by using the loop internally, coupled via an induction loop, and tuning the copper loop via a variable capacitor? I can see this would give a better match to the rx impedance, and stronger signals, but I'm not convinced such is needed with the pre-amp. I've choked back the pre-amp (32dB at 12 volts) by limiting the supply voltage to 6 volts, so I'm guessing probably at about 12 dB gain.

    I've a form of Parkinsons, so constant adjustments (tuning) are an issue, and ill-advised IF not providing substantial benefits.

    Has anyone any practical input for me?
  2. K6CLS

    K6CLS Ham Member QRZ Page

    Hi, good project!

    Can you post some pictures?

    What bands are your interests?

    Sounds like a hot preamp. You must be in a place with clean RF. So not overloading the preamp with broadcast band transmissions, and not needing to tune out any RFI.

    I'd say let the preamp do the work, don't tune the loop.
  3. N6QIC

    N6QIC Ham Member QRZ Page

    You will get a much better response by re-posting to the Antenna forum or to the ham radio discussions forum.

    Thank you,
  4. ZL3BL

    ZL3BL Ham Member QRZ Page

    N6QIC likes this.
  5. N6QIC

    N6QIC Ham Member QRZ Page

    Your Welcome, :)
  6. ZL3BL

    ZL3BL Ham Member QRZ Page

    Bands of interest - HF, primarily 7 and 14 MHz. No photo, nothing of note to see.

    The pre-amp is TINY, but gutsy. A nice aid, but with the disadvantage of being rx only, and the output in dB is somewhat guesswork when one plays with voltage supply, it doesn't seem a linear reduction. I've found that some heat-shrink tubing over the amp makes for good waterproofing, and some ferrite cores on the dc power lead were a wise precaution.

    I have QRM from the new street lights recently installed, hence use of a magnetic loop, to kill the electrical fields received. Directivity, I have found, applies only to very local sources, which makes for some good QRM nulling, without affecting sky-wave reception.

    As to broadcast echoes, part of that is not utuilising max gain on the pre-amp, and using the rig controls (such as rf gain) judiciously. If there were a problem, it's very easy to in-line a blocking filter, set to about 2,2MHz.

    As a simpleton, and physically challenged (mentally challenged is a given!) I adopt the attitude that a simple station has less loss, and less to go wrong.

    Thanks for your response


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