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I called it shadowing but masking may be more appropriate, feel free to suggest a better question title after you read the following.

I have an old clock alarm radio receiver that plays at the center of my living room.

Whenever the antenna wire (a soft, flexible cable) is vertical, if I stand and move to a certain position, North of the receiver, the reception is completely messed up and goes from initially very clear to complete white noise.

I have no idea if I become an obstacle to radio waves or if this is something else.

However I have a hard time believing I prevent radio waves to go to the receiver because the radio emitter, which I visited on the roof of a tall building as I was helping the radio station with computer problems, is not North of my receiver. It is actually West of my receiver. So there is a complete 90 degrees difference of orientation.

But FM broadcast is in the range of 100 MHz (this particular radio station is precisely 95 MHz) which means about 3 meters wavelength and this is in the same range as my height (I am not 3 meters tall, I am 1.83 meter tall, I am talking of scales). So could I act as a dipole of sort?

Maybe the 90 degrees thing just means I am the one getting the radio waves, preventing the receiver to receive them, not by acting like an obstacle, but acting as a competitor.

I also feel this is important I am vertical, just like the antenna, because if I set the antenna horizontally then I do not perturbate the transmission anymore.

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  • $\begingroup$ People can have an electric field, from triboelectriity with a rug, but I have also known a person who set up spark gaps sparking when he went close ( in my days of doing experiments) so this is not a question that can be answered off hand. $\endgroup$
    – anna v
    Jun 25, 2021 at 12:29
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    $\begingroup$ In search and rescue I commonly use 'body blocking' - place my handheld radio near my chest and slowly rotate listening to the Emergency Locater Transmitter (ELT) signal on 121.5MHz. When at a minimum the transmitter is behind me. As one gets closer you use the yagi antenna to get a well define vector. The signal your radio gets strongest may be a reflection or diffraction. $\endgroup$
    – Jon Custer
    Jun 25, 2021 at 12:38
  • $\begingroup$ @anna v: how a static electric field would prevent FM reception? And why would it happen when I am at a certain angle only? $\endgroup$
    – Winston
    Jun 26, 2021 at 9:12
  • $\begingroup$ @jon custer: what is the physical explanation behind this radio blocking? Why MHz radio waves would be blocked by a human body? $\endgroup$
    – Winston
    Jun 26, 2021 at 9:14
  • $\begingroup$ Introduce noise in the electronic circuits? Maybe that angle is vulnerable for the electronic circuits .They might be shielded in the other directions. $\endgroup$
    – anna v
    Jun 26, 2021 at 9:23

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I have found more information about radio blocking by human bodies, either by absorption or reflection, in this page on RF (radio frequency) transmission using body pack microphones in the higher MHz to low GHz ranges:

https://service.shure.com/s/article/does-the-human-body-block-or-absorb-rf-energy?language=en_US

There is a link to an interesting paper that includes lots of data and simulations:

https://d24z4d3zypmncx.cloudfront.net/KnowledgeBaseFiles/effect_human_body_wireless_mic_transmission.pdf

It would seem the human body with its water AND salts make a strong RF absorber, like sea water.

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