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Why do cordless phones give feedback?

L

larrymoencurly

Jan 1, 1970
0
Why has almost every analog cordless phone (not cell) I've tried gives
some whistling feedback when I talk into it? Don't they either use
separate frequencies for the transmission and reception or something
like echo cancellation? The only phone that didn't was a cheap AT&T
49 MHz model that Consumer Reports said was really good, but I kept
losing it because it didn't have a paging function.

I'm using analog because they're about the only 900 MHz phones
available here that don't sound distorted, and I don't want 2.4 GHz or
5.2 GHz because they seem to blank out when wireless networking
equipment or microwave ovens are used.
 
T

the Wiz

Jan 1, 1970
0
Why has almost every analog cordless phone (not cell) I've tried gives
some whistling feedback when I talk into it? Don't they either use
separate frequencies for the transmission and reception or something
like echo cancellation? The only phone that didn't was a cheap AT&T
49 MHz model that Consumer Reports said was really good, but I kept
losing it because it didn't have a paging function.

Probably has something to do with the position you're holding the phone in - as
in it's not against your ear - something that's very common if you're trying to
use the phone "hands free" by tilting your head towards your shoulder.

I have one of those cheap AT&T phones that works pretty well, but WILL give a
feedback squeal if it's placed near a hard surface. The re4ason it doesn't
squeal in normal use is that the microphone isn't very sensitive - people often
ask me to "speak up" when I'm on the cordless phone but never when I'm on the
corded phones..

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Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
johnecarter [email protected] mindspring dot.dot com. Fix the obvious to reply by email.
 
B

Brent

Jan 1, 1970
0
Why has almost every analog cordless phone (not cell) I've tried gives
some whistling feedback when I talk into it? Don't they either use
separate frequencies for the transmission and reception or something
like echo cancellation? The only phone that didn't was a cheap AT&T
49 MHz model that Consumer Reports said was really good, but I kept
losing it because it didn't have a paging function.

I'm using analog because they're about the only 900 MHz phones
available here that don't sound distorted, and I don't want 2.4 GHz or
5.2 GHz because they seem to blank out when wireless networking
equipment or microwave ovens are used.

5.8 (not 5.2) Ghz shouldn't interfere with either of those. 2.4Ghz
interferes with the microwave because microwave and WLAN because they
also operate at 2.4Ghz. Some of the newer 2.4Ghz phones say they will
not interfere with WLAN. I've seen a Vtech that says this.
 
Z

zack

Jan 1, 1970
0
5.8 (not 5.2) Ghz shouldn't interfere with either of those. 2.4Ghz
interferes with the microwave because microwave and WLAN because they
also operate at 2.4Ghz. Some of the newer 2.4Ghz phones say they will
not interfere with WLAN. I've seen a Vtech that says this.


My microwave does not interfere with my 2.4ghz cordless phone unless I
put the phone about 6 inches away from it.. If you get interference
when your phone is more than 2 feet away, then you probably have a
very old microwave and should get it tested for leakage.
 
L

larrymoencurly

Jan 1, 1970
0
Probably has something to do with the position you're holding
the phone in - as in it's not against your ear - something
that's very common if you're trying to use the phone "hands
free" by tilting your head towards your shoulder.

That was one of the first things I thought it was, but even pressing
my ear hard against the phone has never helped.
I have one of those cheap AT&T phones that works pretty well, but
WILL give a feedback squeal if it's placed near a hard surface.
The reason it doesn't squeal in normal use is that the microphone
isn't very sensitive - people often ask me to "speak up" when
I'm on the cordless phone but never when I'm on the corded phones..

The cheap 49 MHz AT&T 4336 that gave me no problems seemed to have a
fairly sensitive microphone, or at least it amplified my own voice
plenty back into the earpiece. Consumer Reports said that another
model with a pager, 4337, was very similar, but they were completely
wrong -- very different internal circuitry, noticeable distortion, and
lots of feedback.
 
S

Shawn Hearn

Jan 1, 1970
0
Why has almost every analog cordless phone (not cell) I've tried gives
some whistling feedback when I talk into it? Don't they either use
separate frequencies for the transmission and reception or something
like echo cancellation? The only phone that didn't was a cheap AT&T
49 MHz model that Consumer Reports said was really good, but I kept
losing it because it didn't have a paging function.

I'm using analog because they're about the only 900 MHz phones
available here that don't sound distorted, and I don't want 2.4 GHz or
5.2 GHz because they seem to blank out when wireless networking
equipment or microwave ovens are used.

I gave up on cordless phones years ago after I got tired of the battery
dying on me at the least convenient moment. I simply have corded phones
now with long cords. That idea might work for you too. You can buy a
corded phone with caller-id for $10 or less and a 50 foot telephone
cable for $1 at many dollar stores.

When I did use cordless phones, I never heard any feedback though.
 
J

Jerry Greenberg

Jan 1, 1970
0
I myself at our office have a few 2.4 gHz phones, one on each tele
line. They are the Panasonic Gigarange series. I have no feedback
problems or any interferance from the microwave oven in the kitchen
area. On our fax line we have a cordless 900 mHz Panasonic phone,
that shares with the fax. This one does not have any problem as well.

The higher end phones have a good quality RF and frequency control
design, where they can select the frequency with the least
interferance, and best reception.

As for the feedback problems, this can be a problem with your
telephone company as well as your phone, consering how their system is
working for the sound duplex. The telephone line is a single twisted
pair that is by-directional. It is possible to have a fault condition
where there is a condition that can have some feedback, depending on
the load on the line and the specifications of the equipment on their
side, and the customer side together.

There is also the condition where the microphone on your phone is too
sensitive, or the return signal back to the telephone companies
equipment is a bit too high. This can cause some feedback. There is
also the condition where the ear piece or recieving signal from the
telephone company is too high.

When you have the feedback condition, try to lower the ear piece
volume on the phone, and see if this gets rid of the feedback. If the
sound is too low, then this can also mean that the microphone is too
loud, or the signal that is being sent back to the telephone company
equipment is too high.

In some of the older cordless phone models, there were internal RX and
TX level pots. The newer phones are mostly controled by internal
software, that is not accessable without the proper service setup.

If you are having the fault condition with many phones, I would guess
the fault to be with the telephone companies equipment, and not yours.
The task would be to have them check this all out for you, and
correct this, if it is the case.


Jerry G.
 
J

JM

Jan 1, 1970
0
quoting:

Sometimes the earpiece can be loud enough that the microphone picks it up.
That makes feedback.
 
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