Can the human body affect a radio receiver?

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So I discover that a human body can affect a radio receiver. When I get close to a receiver, the radio produces buzz sound, which means that the radio signal is disturbed. However when I touch the plastic case of the receiver, the receive becomes normal.

This phenomenon does not happen every time I get close to it; it just happens sometimes. I doubt if certain frequency of radio broadcast is easier to be disturbed.

I think it might due to the electric field of our body. Yet is the field close to FM frequency?

There is another phenomenon I would like to discuss. Why a radio receives better in certain orientation? Isn't the space filled with radio waves already? I think the magnitude of the radio wave is the same in all direction.
 
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  • #2
berkeman
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So I discover that a human body can affect a radio receiver. When I get close to a receiver, the radio produces buzz sound, which means that the radio signal is disturbed. However when I touch the plastic case of the receiver, the receive becomes normal.

This phenomenon does not happen every time I get close to it; it just happens sometimes. I doubt if certain frequency of radio broadcast is easier to be disturbed.

I think it might due to the electric field of our body. Yet is the field close to FM frequency?

There is another phenomenon I would like to discuss. Why a radio receives better in certain orientation? Isn't the space filled with radio waves already? I think the magnitude of the radio wave is the same in all direction.
Do you know what frequency this radio is tuned to when this happens? The human body definitely affects WiFi signals in the 2.4GHz band, and also in other radio bands (2 meter, 70 centimeter HAM radio bands, for example).
Why a radio receives better in certain orientation?
Generally that would have to do with the polarization of the EM waves in the radio signal. Vertical and Horizontal are the two most common polarization types/directions.
 
  • #3
sophiecentaur
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So I discover that a human body can affect a radio receiver.
The effect of your body will depend on the particular wavelength and wavelength can vary from kilometres to centimetres and less. The human body has little effect on the longer wavelengths of Radio Waves. LF, MF and HF have wavelengths that are longer than 2m (human body scale). But people seldom use radio receivers for those wavelengths these days. For shorter wavelengths, a person's body can act like the 'parasitic' elements you can see on rooftop aerials (the H aerial for VHF reception and the more directional UHF TV aerials) Those extra elements are used to make an aerial more directive and get more signal. As mentioned above, some aerials have horizontal wires and some have vertical wires - to receive the particular polarisation better.

All the RF waves in your vicinity are causing tiny currents to flow in your body and these currents follow all the RF signals going past you (yes - thousands of them, all at different frequencies) and re-radiate identical signals. The receiver picks up the wanted signal and also those that your body radiates. Sometimes the signals add up to cause a bigger signal and sometimes they can cancel and then your radio turns up its gain to compensate and the signal can become distorted or buzz - or it may mute itself (in the case of a digital receiver). You can also get the same effect when driving in a car, when multiple signals interfere and cause fluttering and distortion on FM, in particular.

I always struggle to get a reliable DAB signal where we live; the silly dangly wire needs to be draped in just the correct way to avoid muting and sometimes, as you noticed, holding the wire or the receiver will make it all better. RF is funny stuff to deal with unless you have a proper roof-mounted antenna and a downlead to bring a nice beefy signal to your receiver. Set-top TV aerials can be really dodgy too.
 
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  • #4
davenn
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I think the magnitude of the radio wave is the same in all direction.

No it isn't. in the absence of reflections or obstructions, the signal is strongest directly from the transmitter
and when (as @berkeman hinted at) both the transmitting and receiving antennas are of the same polarisation.

There will be times when the direct signal from the transmitter is obscured and the received signal will be from reflections off, say, hills, buildings etc will determine the path and signal strength
 
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  • #5
sophiecentaur
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I think the magnitude of the radio wave is the same in all direction.
You may be referring to the pattern from a very basic antenna - like the vertical mast on many MF transmitting stations - called Omnidirectional. But many antennae are highly directional, with little or no signal in one direction and nearly all the Power directed to where it's needed.
 
  • #6
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Do you know what frequency this radio is tuned to when this happens? The human body definitely affects WiFi signals in the 2.4GHz band, and also in other radio bands (2 meter, 70 centimeter HAM radio bands, for example).

Generally that would have to do with the polarization of the EM waves in the radio signal. Vertical and Horizontal are the two most common polarization types/directions.
The Radio signal is 97.6 MHz. I am wondering that after so many reflections incurred during travelling from the broadcast station to my home, the magnitude in both horizontal and vertical polarization is roughly the same.
 
  • #7
berkeman
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The Radio signal is 97.6 MHz. I am wondering that after so many reflections incurred during travelling from the broadcast station to my home, the magnitude in both horizontal and vertical polarization is roughly the same.
It is true that reflections from some angled surfaces can rotate the angle of polarization, and multi-path signals can create nulls where the multiple signals destructively interfere, leaving very little net signal to be picked up by the receiving antenna. That's the main reason for the "antenna spatial diversity" that you see on some WiFi Routers and other RF devices that use frequencies and are used in environments where multipath is a big issue. If one of the antennas is in a receiving null due to multipath interference, the other one generally will not be in a null.

https://i.ebayimg.com/images/g/Vo8AAOSw7aBVDB-p/s-l1600.jpg

1597925391699.png
 
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  • #8
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It is true that reflections from some angled surfaces can rotate the angle of polarization, and multi-path signals can create nulls where the multiple signals destructively interfere, leaving very little net signal to be picked up by the receiving antenna. That's the main reason for the "antenna spatial diversity" that you see on some WiFi Routers and other RF devices that use frequencies and are used in environments where multipath is a big issue. If one of the antennas is in a receiving null due to multipath interference, the other one generally will not be in a null.

https://i.ebayimg.com/images/g/Vo8AAOSw7aBVDB-p/s-l1600.jpg

View attachment 268037
One more question: why does the receiver receive better when I touch its case? Either touching the metal antenna or the plastic case improves the receive. I always listen to radio and therefore I am quite interested in these phenomena :).
 
  • #9
berkeman
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One more question: why does the receiver receive better when I touch its case? Either touching the metal antenna or the plastic case improves the receive. I always listen to radio and therefore I am quite interested in these phenomena :).
As @sophiecentaur says in Post #3, there are lots of parasitic effects that can add or detract from the receive performance of an antenna and radio receiver. If there is a multipath interference issue, you may alter that multipath null by your presence and/or your contact. If your antenna and radio receiver are working well, touching the antenna will generally degrade the performance.
 
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  • #10
DrClaude
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If your antenna and radio receiver are working well, touching the antenna will generally degrade the performance.
On the other hand, I remember a friend and I taking turns holding one of the bunny ears of a TV set in order to be able to reduce the static to the point where we could actually follow the puck in a hockey game.

I am getting old :frown:
 
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  • #11
berkeman
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I remember a friend and I taking turns holding one of the bunny ears of a TV set in order to be able to reduce the static to the point where we could actually follow the puck in a hockey game.
I posted a thread a while back about my Digitial TV antenna/receiver hacks... :wink:

1597936032583.png


So the quality of my over-the-air digital TV reception has been getting worse over the past few months. Probably the digital TV antenna that I'm using is getting old and starting to degrade. Last night I resorted to trying different reflector combinations to try to boost the signal for the horizontal UHF dipole antenna (inside the rotator disc on the top of the antenna unit). I could hand-hold it in a reasonable reflector position, but it was hard to figure out a way to mount it permanently.

So I went the fractal reflector route shown in the picture below (the antenna unit was already hanging from the ceiling). It actually worked a lot better than I expected, but it probably won't work for all stations (since you have to use the rotation function to find the best direction to point the UHF dipole in the disc -- the local stations are spread through about a 90 degree arc to my north.

Anyway, it looks like it's time to spring for a new over-the-air digital TV antenna. We live in a 2nd floor apartment and the TV is next to the balcony, so I could probably camouflage a fairly large antenna below the railing if that would help. (I already have a camouflage HAM radio antenna on the balcony). Does anybody have any suggestions for good digital TV antennas (USA models)? Clearly it needs to have rotational capability (or phased array capability, if that exists for digital TV antennas).

Thanks for any ideas! :smile:

View attachment 212357
 
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  • #12
Mister T
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When I get close to a receiver, the radio produces buzz sound, which means that the radio signal is disturbed.
This could be due to other devices that share the same circuit as the radio. Try plugging the radio into some different outlets in your home. Or if you don't want to move the radio you could try moving other appliances that share the same circuit as the radio.
 
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  • #13
sophiecentaur
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“Other devices” can have mains leads that act as parasitics at VHF. It’s basically a mess!!!! The VHF bands (up to about 100MHz) were planned and allocated assuming people would use a rooftop aerial. (Vertical polarization because car ignition interference was a bit less got VP. - omg this was really thought through in UK) VHF radio was an attempt at really HIGH QUALITY sound. But people wanted portability and the whip aerial on your VHF tranny radio totally put the mockers on it. It got to be the same as the set top aerial on the TVs of the USA. Russian Roulette of Reception!
lucky people who live in the right place will not recognize this (lol).
 
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  • #14
.Scott
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For wavelengths greater than about a meter humans (aka, ugly bags of mostly water) are basically electrical conductors - with some absorption and electrical resistance.
Liquid water absorption.

The human body taken as a whole, is particularly good at absorbing radio waves at 6 meters (VHF):
Human body absorption of radio waves.

So we can both block signals and conduct them - and at times we can become pretty good antennae. In many cases, we can also act as a capacitive connection to ground - or other signal source (such as a computer or noise in the power lines).

And, as already mentioned earlier in this thread, this could have a very big effect on analogue TV reception - especially when an improvised antenna was used at the TV. Not only would the antenna need to be reconfigured for each TV station, but you needed to set it and return to your seat to see the result. Then repeat this process until you had good enough reception. Then someone else would start to pass through the room - and at some critical point, they would create the perfect reception. Of course, the temptation was to attempt to negotiate with them to hold that position.
 
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  • #15
sophiecentaur
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a very big effect on analogue TV reception
Many parts of the world just don't do Analogue TV any more. It's heading away from broadcasting and all the data we send and receive will, before long, be on a common network. I don't know the exact future, of course and there will always be a decision as to what goes over the air and which goes on fibre. Either way, we will probably be unaware how it gets to us.

Our toaster will tell our coffee maker when to pour our cup of coffee, via satellite, in the morning.
 
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