micky <NONONOmisc07@fmguy.com>: Dec 25 01:34PM -0500
Technical qustion about wave valleys and troughs and if two radio
playing the same station will be in phase wrt all frequencies, or if
some will cancel out?
And why is it low frequencies are famous for cancelling out when out of
phase when high frequencies are just as likely, 0.5, I think, to cancel
each other out?
Can I just turn off one radio and turn it on again so that the total
odds over both times have increased that by the second time the radios
will be in phase?
I have a radio and tv in one bathroom but neither in the other, which is
smaller and adjoins the bedroom. Sometimes I want to hear the radio
which only gets 'loud' if you are in the same room. I can hear it from
the bathroom but not enough to understand what is said.
I have another table radio, KLM, expensive, that I had for about 33
years when the speaker switch started to fail**, and I turn that one on
too, to the same station, also at maximum volume, and I can hear in the
bathroom just fine, but I wonder if some frequencies are out of phase
from one radio to the other, cancelling each other, and I'm not hearing
them.
It seems to me, if one radio is farther from the transmitting antenna,
by 1/2 wave length, the speakers in the two radios will always be going
in the opposite direction from each other. Maybe.
In my case, the radios are one above the other, so the distance from the
xmtr is very similar. But what about within the radio, when the
heterodyning frequency starts. What if it starts have a cycle after the
first radio?
**So I bought the second radio. The first one has a pushbutton switch
meant to connect/disconnect a wooden-cabinet stereo speaker, which I
have no room for, and unless I get the switch just right, no sound comes
out at all. (even the on/off momementary contact switch no longer works
well, after only 33 years, maybe using it at most 6 times a day, so that
6x365x33=66,000 times. Aren't switches supposed to last into the
millions of times? --- It's failing isn't nearly as bad, because I just
keep pushing until it works. The speaker switch OTOH has a spring that
pushes it out, past its sweet spot, so now it's hard to get to connect
at all.
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micky <NONONOmisc07@fmguy.com>: Dec 25 04:12PM -0500
sci.electronics.design added.
Technical qustion about wave valleys and troughs and if two radio
playing the same station will be in phase wrt all frequencies, or if
some will cancel out?
And why is it low frequencies are famous for cancelling out when out of
phase when high frequencies are just as likely, 0.5, I think, to cancel
each other out?
Can I just turn off one radio for a few seconds and turn it on again so
that the total odds over both times have increased that by the second
time the radios will be in phase?
I have a radio and tv in one bathroom but neither in the other, which is
smaller and adjoins the bedroom. Sometimes I want to hear the radio
which only gets 'loud' if you are in the same room. I can hear it from
the bathroom but not enough to understand what is said.
I have another table radio, KLM, expensive, that I had for about 33
years when the speaker switch started to fail**, and I turn that one on
too, to the same station, also at maximum volume, and I can hear in the
bathroom just fine, but I wonder if some frequencies are out of phase
from one radio to the other, cancelling each other, and I'm not hearing
them.
It seems to me, if one radio is farther from the transmitting antenna,
by 1/2 wave length, the speakers in the two radios will always be going
in the opposite direction from each other. Maybe.
In my case, the radios are one above the other, so the distance from the
xmtr is very similar. But what about within the radio, when the
heterodyning frequency starts. What if it starts have a cycle after the
first radio?
**So I bought the second radio. The first one has a pushbutton switch
meant to connect/disconnect a wooden-cabinet stereo speaker, which I
have no room for, and unless I get the switch just right, no sound comes
out at all. (even the on/off momementary contact switch no longer works
well, after only 33 years, maybe using it at most 6 times a day, so that
6x365x33=66,000 times. Aren't switches supposed to last into the
millions of times? --- It's failing isn't nearly as bad, because I just
keep pushing until it works. The speaker switch OTOH has a spring that
pushes it out, past its sweet spot, so now it's hard to get to connect
at all.
|
Ed Cryer <ed@somewhere.in.the.uk>: Dec 25 09:13PM
micky wrote:
> keep pushing until it works. The speaker switch OTOH has a spring that
> pushes it out, past its sweet spot, so now it's hard to get to connect
> at all.
Let's rule out Hertzian waves from Net speeds to begin with. If you have
an FM radio and a Wifi radio in the same room, there'll be a very
noticeable discrepancy.
This phenomenon is so well known that I don't need linger on the cause.
Added to that, you may have two wifi radios together, but processed by
different hardware/ software. And here again the cause needs no explanation.
Your second radio with the dodgy on/off button doesn't even contribute
to the mix; and it won't do so until it produces some output sound. A
faulty switch is a different problem from an echoing, out-of-sync
cacophony of sound.
Ed
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Ed Cryer <ed@somewhere.in.the.uk>: Dec 25 09:29PM
Ed Cryer wrote:
> faulty switch is a different problem from an echoing, out-of-sync
> cacophony of sound.
> Ed
My best radio is in my bathroom. I didn't put it there; it was in place
when I moved in; it comes through the vent fan which switches on with
the room switch.
I've been trying to figure out for years which station it's tuned to.
Mostly it seems classical, like a choir singing, but now and again it
has a bom-da-da-bom rhythm of rock music. I once heard it playing
Werewolves of London.
If you solve your problem, let me know. I'd love to find out which
station my bathroom is tuned into.
Ed
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John Larkin <jlarkin@highlandSNIPMEtechnology.com>: Dec 25 01:31PM -0800
On Sun, 25 Dec 2022 16:12:19 -0500, micky <NONONOmisc07@fmguy.com>
wrote:
>Can I just turn off one radio for a few seconds and turn it on again so
>that the total odds over both times have increased that by the second
>time the radios will be in phase?
Phase is probably constant for each radio, but random between
different types.
Measure it.
Sound waves are short so you'd have to be equidistant from both
speakers, without wall reflections, to have phasing mean much.
>keep pushing until it works. The speaker switch OTOH has a spring that
>pushes it out, past its sweet spot, so now it's hard to get to connect
>at all.
Try some contact cleaner.
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micky <NONONOmisc07@fmguy.com>: Dec 25 05:55PM -0500
In alt.home.repair, on Sun, 25 Dec 2022 16:56:38 -0500, Rachelle
>> some will cancel out?
>Are the radios powered by the same 120v phase or on opposite legs (180
>degree out-of-phase)?
Yes, plugged into the same outlet.
Both are traditional over-the-air AM-FM radios, usually using FM. (One
has bluetooth but it's not in use. )
(To other poster, The radio with the bad speaker switch works well if
the switch stops in the right spot, and sometimes it will stay that way
for days. No access for contact cleaner at the moment.
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rbowman <bowman@montana.com>: Dec 26 12:12AM
On Sun, 25 Dec 2022 21:29:49 +0000, Ed Cryer wrote:
> If you solve your problem, let me know. I'd love to find out which
> station my bathroom is tuned into.
Don't you have another radio? It would be trivial to scan the frequencies
until you get a match. Doesn't the UK require broadcast stations to
periodically identify themselves?
https://www.transmissionzero.co.uk/radio/london-pirate-radio/
Perhaps it's a pirate with eclectic taste. The local university has a low
power FM station that's all over the map depending on who the DJ is for
the slot.
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dplatt@coop.radagast.org (Dave Platt): Dec 25 09:54PM -0800
In article <m3fhqhpa8r1b700ol2pk2j6ru33aol4r47@4ax.com>,
>Technical qustion about wave valleys and troughs and if two radio
>playing the same station will be in phase wrt all frequencies, or if
>some will cancel out?
To a very close approximation, the movement of their speaker cones
will be in phase (assuming that the radios are of identical design).
The speed of light (and radio) is fast enough that you need a lot of
separation between two identical radios, before the outputs will
develop a perceptible phase shift.
The in-phase-vs-out-of-phase behavior at the actual listening location,
and its effect on specific frequencies, is dominated by the distance
from each speaker cone to the listener's ear. Since sound moves at only
about 1 foot per millisecond, changing the distances by an inch or two can
make a big difference in which frequencies cancel and which ones reinforce.
>And why is it low frequencies are famous for cancelling out when out of
>phase when high frequencies are just as likely, 0.5, I think, to cancel
>each other out?
They do. However, you're less likely to notice it, for a number of
reasons.
At the higher frequencies, our ears (and brains) are constantly
dealing with the reinforcement and cancellation of different
frequencies, as the sound waves bounce off of floors and ceilings and
create all sorts of "multipath" interference which changes every time
we move a few inches. This happens even for a single sound source
(mono radio, person speaking, etc.). Our brains have evolved to
perceive sound sources even in the face of this sort of multipath
interference and the resulting "comb filter" effect. So, we just
don't notice it consciously when it's happening. You can see the
effect on a spectrogram (pick up the REW software and a good
microphone if you want to experiment).
>Can I just turn off one radio for a few seconds and turn it on again so
>that the total odds over both times have increased that by the second
>time the radios will be in phase?
"In phase" where and at what frequencies? At the speaker cones? At
your current listening position? At the position you'll be in ten
seconds, after you move your head a bit?
>bathroom just fine, but I wonder if some frequencies are out of phase
>from one radio to the other, cancelling each other, and I'm not hearing
>them.
Look at it this way. At a frequency of 1000 Hz (roughly in the middle
of the speech-frequency range), a full wave of the sound is about a
foot long (in air). If you stand between the two radios, and then
move three inches one way or the other, you'll increase one path
length by a quarter-wavelength and reduce the other by a
quarter-wavelength, and thus change the timing difference by half
a wavelength. You'll go from "reinforcement" to "cancellation" (or
vice versa) at this one frequency, just by making this simple little
movement of your head.
At higher frequencies, moving as little as an inch has this same
effect. At lower frequencies, yoh have to move further to change
cancellation into reinforcement.
As you move, you're probably also going to be changing the collection of
reflective paths from each radio to your head, and these changes will
also alter the cancellations and reinforcements. "Multipath" can be
extremely complicated.
>It seems to me, if one radio is farther from the transmitting antenna,
>by 1/2 wave length, the speakers in the two radios will always be going
>in the opposite direction from each other. Maybe.
No, that's too simple a model of how the sound-in-air is related to the
signal-by-radio. It doesn't really work that way.
In FM radio, the position of the speaker cone (pushed towards you or
pulled back to you) depends on the frequency of the RF (above or below
the nominal FM carrier frequency), *not* on the phase of the RF at any
given instant. Delaying the RF by a few cycles will result in only a
negligible delay in the phase of the speaker cone
motion... approximately 1 nanosecond of timing change per foot.
AM detection works somewhat similarly, in that the amplitude of the
signal fed to the speaker is proportional to the _envelope_ of the
RF signal, and not to its instantaneous value or phase.
So, in both AM and FM, the amount of phase shift in the speaker-cone
output caused by moving the radio towards, or away from the transmitter
is tiny. The effect of changing the length of the sound path (in air)
between radio and listener are far, far larger.
(Move the radio 1 foot closer to the transmitter, and you change the
speaker-cone timing by at most a nanosecond or so. At the same time,
you change the speaker-cone-to-ear sound travel timing by as much as
a millisecond. That's a million-to-one difference! Radio fast, sound
slow.)
>xmtr is very similar. But what about within the radio, when the
>heterodyning frequency starts. What if it starts have a cycle after the
>first radio?
Essentially irrelevant, once the heterodyned IF signal hits the
detector (FM detector such as a ratio or quadrature detector, or an AM
envelope or product detector). At this point, the heterodyned IF
signal per se ceases to exist, and we start looking at an audio signal
which is based on a longer-term "measurement" of the IF (its envelope,
or its frequency deviation from nominal center) which doesn't depend
significantly on the phase of the IF or the original RF.
>well, after only 33 years, maybe using it at most 6 times a day, so that
>6x365x33=66,000 times. Aren't switches supposed to last into the
>millions of times?
Switches and relays are (in my experience) often the weakest point in
radios and etc. The contacts wear out or bend, the contacts get dirty or
contaminated (tobacco and cannabis smoke leave a nasty, insulating tar),
the plastic switch body wears out, etc.
Yes, they may be "supposed to" last for hundreds of thousands, or even
millions of cycles, *if* the manufacturer chose a really good switch
and if it's been kept clean. Often, neither of these is the case.
OEMs often "economize" on such things to save a few cents per unit.
If it lasts until after the warranty expires... for many brands,
that's plenty good enough.
I've gotten quite a few radios and so forth "back from the dead" by giving
switches a good cleaning, or (when necessary) replacing them.
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Martin Brown <'''newspam'''@nonad.co.uk>: Dec 26 09:30AM
On 25/12/2022 22:55, micky wrote:
>> Are the radios powered by the same 120v phase or on opposite legs (180
>> degree out-of-phase)?
> Yes, plugged into the same outlet.
The radio will convert it to DC anyway so that doesn't matter.
> Both are traditional over-the-air AM-FM radios, usually using FM. (One
> has bluetooth but it's not in use. )
Chances are one will be a few hundred ns time shifted relative to the
other since the amplifiers in each stage of detection are unlikely to
have exactly the same delay or frequency phase response.
Propagation of sound waves in the room will have a much larger effect on
what you hear. Positioning of the speakers relative to hard surfaces.
> (To other poster, The radio with the bad speaker switch works well if
> the switch stops in the right spot, and sometimes it will stay that way
> for days. No access for contact cleaner at the moment.
If you really want massive flanging effects try two different digital
radios or SDR decoders within earshot. The difference in delays then can
be fractions of a second or seconds when compared to an FM radio.
DAB is completely useless in an emergency situation unless you have a
shed load of batteries. Uses a set every 8 hours of run time. A decent
FM radio will run for a week or more on just one set of batteries.
--
Regards,
Martin Brown
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Clive Arthur <clive@nowaytoday.co.uk>: Dec 26 10:48AM
On 25/12/2022 22:55, micky wrote:
> (To other poster, The radio with the bad speaker switch works well if
> the switch stops in the right spot, and sometimes it will stay that way
> for days. No access for contact cleaner at the moment.
I would expect two radios of the same make and model to be in phase, but
different radios will have different amplifier designs and speaker
arrangements which will likely give phase differences at different
frequencies. Plus it is possible that the two loudspeakers are simply
connected in opposite polarity anyway.
--
Cheers
Clive
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upsidedown@downunder.com: Dec 26 02:49PM +0200
On Sun, 25 Dec 2022 17:55:35 -0500, micky <NONONOmisc07@fmguy.com>
wrote:
>Both are traditional over-the-air AM-FM radios, usually using FM.
Even if two radios produce in phase audio on AM (with equal number of
audio inverting stages) the radio may produce opposite phase audio on
FM. One might have the local oscillator (LO) below the received
frequency (RF), while in the other the LO is above the RF frequency.
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