Frans purchases the Hurricane AM Modulator

Many thanks to SWLing Post contributor, Frans Goddijn, who writes:

I bought the Hurricane AM Modulator.

Here in my living room the hum was considerable even though I had an EARTH connection. So what I did was use a coax cable made of two different ends of coax cable, just the isolated kernel of both taped close together so the signal is transmitted on one, received on the other without the wires touching. One end in the antenna OUT of the transmitter, the other end in antenna IN of the receiver.

Now I can wirelessly send music from my laptop or telephone to the Hurricane and ‘receive’ it on the radio of my preference.

The HUM obviously does not originate from the Hurricane.

Click here to view on YouTube.

Best regards!


Click here to check out the Hurricane AM transmitter on eBay.

Thank you for sharing this, Frans. The Hurricane sounds amazing via that gorgeous Hammarlund SP-600! 

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13 thoughts on “Frans purchases the Hurricane AM Modulator

  1. David Esp

    For me – in an upstairs apartment – the hum came primarily from part of the signal leaking “backwards” through the switched-mode power plug. Confirmed by different power plugs causing different degrees of hum, and ultimately (explained below) using a balanced antenna (not requiring an earth).

    In this kind of location (upstairs apartment), no “proper earth” is possible, but (prior to using a balanced antenna), connecting to the mains earth helped (with the side effect of radiating throughout the building).

    The “switch-mode” action of the power plug (diodes or whatever opening and closing at mains frequency) essentially modulates that portion of the signal (on its own – essentially within the antenna system – independently of the unit’s modulator).

    For my situation, the neatest solution has been to transmit instead into a resonant loop/frame antenna. Can be as big or small as wished, depending on desired range. Main advantage: doesn’t require an earth – because it is a balanced antenna. Except that the cable feeding it can also act as an antenna with respect to earth (e.g. via the power-plug). However the output from the loop dominates that sufficiently.

    I also fitted a ferrite ring to the power plug’s lead to the unit, to attenuate the “leakage” RF. Seems to reduce it a bit – but not 100%.

    Prior to that I had also tried fitting an optical isolator in the audio-in connection, which had surprisingly (at the time) little benefit. Regardless, for ultimate audio earth-loop isolation, I have ended up using the Hurricane’s Bluetooth audio input – because it’s reliable, provides a good audio quality audio and also it’s nice to have fewer cables (to tangle-up, pick up other people’s RF etc.) and for the audio source (e.g. a laptop running a player or playout app) to be in-room portable.

  2. Frans

    This evening I used the INC button on the front to increase frequency to 2016 kHz and now there is no hum or other noise audible on my setup.

  3. Chris Hunter

    I found that moving the aerial away from the house helped enormously, and using hum cancellation got rid of the last vestiges of it altogether. My little AM set up sounds superb, using a four chip MW synthesiser (4060, 40103, 4046 and 4013 (to give an equal mark / space ratio) and a PWM modulator using a 4053, followed by a little two transistor linear amplifier. The modulator itself uses a couple of dual op-amps and a THAT4301 audio processing IC to give accurate modulation depth compression and limiting. I’ve been very pleased with the results!

  4. Tony Williams

    Ken suggested “Maybe running the AM transmitter on batteries would resolve the hum”

    Noop… almost always makes no difference whatsover…

    Reason is…

    (What follows assumes the following… Antenna is inside house, Transmitter Earthed and the Power Supply is good quality)..

    1. Transmitters antenna is short (re FCC rules) and is close to house wiring (in an average room you are never more then 6-10ft away from mains wiring…
    2. House wiring is an ideal antenna being many hundreads of feet long… (random wire antenna)
    3. Unfortunately it also has 50/60hz mains at 115/230v ..
    4. result is it re-transmits the signal with the hum…

    Solution is to move the transmitter antenna away from house wiring..
    One way to do this is to use coax to feed an external antenna whilst keeping the transmitter inside..
    Also try antenna in vertical & horizontal position this sometimes helps
    Quite often changing the frequency will also reduce or ever get rid of the hum
    Its just trial and error…

    The last two animations in the video show what happens…

    (hope this helps)…

  5. Chris Hunter

    The hum issue is unlikely to be due to the modulator. It’s almost certain to be mixing with the mains 50 / 60 Hz (according to where in the world you are), as described on the 6V6 “help” page.

  6. Ken Cobld

    I have a bunch of Joe Frank monologues and old radio shóws from the 1930s thru the 1950s that would keep a AM micro transmitter busy for years has a lot of vintage radio shows you can download free

  7. Bill KI7HYI

    I have to wonder if hum would be a problem in a PWM AM modulator like the one used in the Rockwell/Collins Power Rock MW transmitter.

      1. frans

        I also tried a good old “Delta Elektronica” lab power supply which did not make a difference. The “earth’ connection dimmed it a bit but ‘twining’ the coax cables eliminated it so for no I will keep it that way until I feel like experimenting more.

  8. Chris Hunter

    Getting rid of hum on small AM transmitters is one of the “black arts”! There is a lot written about it on the American “” website. My little Part 15 transmitter (running around 100mW into a short whip aerial) has a useful range of around ¾ mile, and the trickiest part of setting it up was nulling the hum that was partially induced from the mains. My resoltion for the issue was a “humdinger” – a trick that was frequently used in tape recorders. You introduce some low-level 50 Hz signal in the appropriate phase to null the hum out – if done carefully, it results in a completely clean signal.


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