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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: IR detector system, biasing of photo diode
Date: Tue, 29 Oct 2024 05:02:33 -0700
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On 10/29/2024 4:20 AM, Liz Tuddenham wrote:
> Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
> 
> [...]
>>
>> If the chirp arrives at the same time at each mike, the robot is on the
>> right path, If one is delayed, the robot eases into the that direction
> 
> If one of  the chirps has been reflected from a distant hard surface the
> long delay could interfere with the next pulse.  Something like that
> happened to an early-warning radar sytem when the moon rose and
> reflected long-delayed pulses.
> 
> A slow pulse rate or a variable one would overcome this.

ISTR Polaroid's ultrasonic ranging kit; the transducer was driven
with pulses in a fixed pattern at four distinct frequencies.
This helped the receiver determine the "envelope" for a single burst.

In LORAN, the carrier was modulated with a specific envelope
(as well as a pulse code pattern) to let the receiver identify
a specific reference point on the carrier.  (because multiple
signal sources could be present in a given geographical area)