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Re: LF: Sine wave/Sq wave

from [Andy Talbot] [Permanent Link][Original]
To: LineOne <[email protected]>
Subject: Re: LF: Sine wave/Sq wave
From: Andy Talbot <[email protected]>
Date: Fri, 7 Sep 2018 15:42:08 +0100
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Unfortunately, 0dBm from a 50R source into a Schmitt isn't enough in many cases.     74HC series logic has Schmitt thresholds at 30% and 70% of supply volts, which if 5V needs at least 2V pk-pk.  At 50 ohms this is +10dBm absolute minimum.     

74HCT series has thresholds of 1.6 and 2V (ish ish) , but even those are too far apart to absolutely guarantee getting a square wave from 0dBm

A line receiver, like the 26LS32 mentioned or a CMOS equivalent has 100mV or 200mV hysteresis and does a much better job.

Or even an opamp with a bit of positive feedback for a few tens of mV  hysteresis.


On 7 September 2018 at 15:20, <[email protected]> wrote:
LF/MF
Someone was asking about converting sine wave to Sq wave recently from a TS590 to drive an Amplifier
Feed the DRV output sine wave  from the TS590 to a Schmitt triger cct and then use a Direct Amplifier similar to the Decca 5501 class D bridge amp.
I use this method on LF es MF and never had a problem.
 
73 gl de mal/g3kev
 
 

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