Brenda Ann wrote:


"Bob Dobbs" wrote in message
news:49eb5ac5.4793609@chupacabra...
dave wrote:
Telamon wrote:


Well, how about analog? I have some hiss in there all the time and
often times warbling rumble kind of noise. It's very annoying and I
wish they would turn that HD crap off.


The IBOC signal is either side of the AM carrier. Each IBOC sideband is
identical but out-of-phase with the other. The theory is the IBOC
sidebands cancel each other out in your receiver. But if one sideband
propagates better than the other (which is always the case once you get
a few miles from the transmitter) the cancellation is not complete.
This is when you hear the digital hash and the wubba-wubba sound.

For those of us using a radio with selectable sideband synchronous
detection, but unable to choose USB and LSB at the same time (like my
Drake SW2) we are forced to listen in plain AM.



The theory doesn't even work well within the local signal area, since
almost no radios use a detector that detects both sides of the envelope.
Therefore, you have only one sideband being detected, and the IBOC hash
will be present under the analog program material if the radio is
sufficiently broadband (more than about 8 KHz).

Most AM radios detect the signals on both sides of the carrier. I know of no
commonly available radio that doesn't operate that way in the AM mode.

Detecting the positive or negative side of the AM envelope in the time
domain does not equate to detecting USB or LSB. (i.e., a simple diode
detector.)

The need for DSB in the sync mode is to cancel out components of the digital
signal in the passband of the radio, not deal with the bulk of the digital
signal that is well outside of the passband.