Re: LF: Sine wave/Sq wave

[Andy Talbot <andy.g4jnt@gmail.com>]

When I did this, for the -4dBm out from a DDS source, I designed a custom filter for the DDS anti-aliassing that had asymmetric termination impedances and provided a voltage step-up. (AADE filter designer allows this option)    Then into a  line receiver - I forget which type exactly, there are millions all suitable.  Built back in 2000 or thereabout and still working to this day on 137kHz. For low level from a transceiver output, you could use a step up transformer into, say 300 ohms, for a voltage magnification of 2.5 ish 

Andy

www.g4jnt.com

On 7 September 2018 at 15:42, Andy Talbot <andy.g4jnt@gmail.com> wrote:

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.

Andy

www.g4jnt.com

On 7 September 2018 at 15:20, <g3kevmal@talktalk.net> 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