Am I an antenna?

[The_Ryan]

I’ve noticed that often when watching broadcast television (that is, from the antenna, not cable), the quality of the reception will depend on where I’m standing. Is the human body capable of modifying EM transmissions? Also, I’ve noticed that the quality of playback of tapes that I have already recorded will depend on where my antennas are placed. Any ideas why this could be?

[Sublight]

First question:

According to Cecil, it’s because your body is a good conductor of electricity and acts like a larger antenna.

http://www.straightdope.com/mailbag/mstatic.html

Second question:

No idea. Sorry.

[David_Simmons]

*Originally posted by The Ryan *
**I’ve noticed that often when watching broadcast television (that is, from the antenna, not cable), the quality of the reception will depend on where I’m standing. Is the human body capable of modifying EM transmissions? Also, I’ve noticed that the quality of playback of tapes that I have already recorded will depend on where my antennas are placed. Any ideas why this could be? **

As Sublight said that Cecil said, yes you can act as an antenna. And sometimes parts of you can act as a detector. People have been known to receive and detect radio signals when near an AM transmitter antenna. Non-linear electrical conduction in tooth fillings detects the modulation and they hear the audio through bone conduction.

[Una_Persson]

What’s the frequency, Ryan?

[whitetho]

One quick note: “mailbag” links are not written by Unca Cece – Sublight’s link was instead written by one “SDSTAFF Tech”. However, Cecil did write a column about radio reception by dental work, Is it possible to hear radio broadcasts through your teeth?, which is included in his third opus, Return of the Straight Dope.

Adding to what others have said, there are at least two possible ways for the human body to affect reception. The first is when you touch or stand close to the antenna, and your “body capacity” changes the antenna characteristics. However, there is a second case when you are standing farther away, and your body can reflects the signals – particularly in the case of the shorter wavelengths used by FM and TV. Thus, standing in different parts of the room can hurt or help reception. Similarly, overflying airplanes and even trees can have an effect. The shorter the wavelength the more visible the impact. I particularly notice it on weak UHF TV signals during windy days, since I am located near numerous trees which sway in the wind.

You might find the following from the 1922 Radio Boys Trailing a Voice interesting:

Bob had been working steadily, and, as the room was warm, his hands were moist with perspiration. He had unhooked an insulated copper wire that led to his outside aerial. His head phones were on, as he had been listening to the radio concert while he worked.
    “I’ll have to miss the rest of that selection, I guess,” he remarked regretfully, as he unhooked the wire. “It’s a pity, too, for that’s one of the finest violin solos I ever heard. Great Scott! What does that mean?”
    The ejaculation was wrenched from him by the fact that although he had disconnected the wire he still heard the music–a little fainter than before but still with every note distinct.
    He could scarcely believe his ears and looked at his friends in great bewilderment.
    “What’s the matter?” asked Joe, jumping to his feet. “Get a shock?”
    “Not in the sense you mean, but in another way, yes,” replied Bob, still holding the exposed end of the copper wire in his fingers. “What do you think of that, fellows? I’m an aerial!”
    “Come out of your trance,” adjured Herb unbelievingly. “They talk that way in the insane asylums.”
    “Clap on your headphones,” cried Bob, too intent on his discovery to pay any attention to the gibe.
    They did so, and were amazed at hearing the selection as plainly as did Bob himself.
    The latter had been holding the disconnected wire so that his fingers just touched the uncovered copper portion at the end. Now he hastily scraped off several inches of the insulation and grasped the copper wire with his hand. Instantly the volume of sound grew perceptibly greater.
    Hardly knowing what to make of it, he scraped off still more of the insulation.
    “Here, you fellows,” he shouted. “Each of you take hold of this.”
    Joe was the first to respond, and the sound became louder. Then Herb and Jimmy followed suit, and it was evident that they served as amplifiers, for with each additional hand the music swelled to greater volume.
    The boys looked at each other as if asking whether this was all real or if they had suddenly been transferred to some realm of fancy. They would not have been greatly surprised to wake up suddenly and find that they had been dreaming.
    But there was no delusion about it and they listened without saying another word until, in a glorious strain of melody, the selection came to an end. Nor did they break the silence until a band orchestra was announced and crashed into a brilliant overture.
    While it was still in full swing, Bob had an inspiration. He took off his headphones and clamped them on to the phonograph that stood on a table near by. Instantly the music became intensified and filled the room. When all their hands were on the wire, it became so loud that they had to close the doors of the phonograph.
    “Well,” gasped Bob, when the last strain had died away and the demonstration was complete, “that’s something new on me.”
    “Never dreamed of anything like it,” said Joe, sinking back in his chair. “Of course we know that the human body has electrical capacity and that operators sometimes have to use metal shields to protect the tube from the influence of the hand. And in our loop aerial at Ocean Point you noticed that the receptivity of the tube was modified when we touched it with our fingers.”
    “Of course, in theory,” observed Bob thoughtfully, “the human body possesses inductance as well as capacity, and so might serve as an antenna. But I never thought of demonstrating it in practice.”
    “So Bob is an aerial,” grinned Herb. “I always knew he was a ‘live wire,’ but I never figured him out as an antenna.”
    “And don’t forget that if Bob is an aerial we’re amplifiers,” put in Jimmy.
    “There’s glory enough for all,” laughed Joe. “We’ll have to tell Doctor Dale and Frank Brandon about this. We’ve got so many tips from them that it’s about time we made it the other way around.”

[Boyo_Jim]

About your second question, tape playback.

Are you feeding the signal to the TV through audio/video ins and outs, or through the TV’s antenna in?