Speaker => line out matching (packet radio) - Electronic Circuits Projects Diagrams Free

Blue Dog · 15th April 2008, 04:52 PM

I'm building a packet interface for a amateur radio, the tranceiver doesn't have a line out and the schematic calls for a 1k-8ohm transformer for the match, the closest I can find locally is 1k2 - 8 - any thoughts on this?

VE3GKN

audioguru · 15th April 2008, 05:24 PM

A 1k to 8 ohms transformer will attenuate a 2V signal 11.2 times to 179mV.
A 1.2k to 8 ohm transformer will attenuate the 2V signal to 163mV.
The difference is only 1dB which is not noticeable.

Why a transformer? Why not two resistors instead?

Blue Dog · 15th April 2008, 05:40 PM

Thanks for confirming my suspicions and for knowing/doing the math

I think the matching transformer is being used to eliminate any potential ground loop hum on the signal and more importantly, to reduce the risk of any damage to the computer or radio from any difference in voltage potential - guess it does double duty by acting as an isloation transformer as well as doing the match.

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15th April 2008, 04:52 PM	(permalink)
Blue Dog	Speaker => line out matching (packet radio) I'm building a packet interface for a amateur radio, the tranceiver doesn't have a line out and the schematic calls for a 1k-8ohm transformer for the match, the closest I can find locally is 1k2 - 8 - any thoughts on this? VE3GKN

15th April 2008, 05:24 PM	(permalink)
audioguru	A 1k to 8 ohms transformer will attenuate a 2V signal 11.2 times to 179mV. A 1.2k to 8 ohm transformer will attenuate the 2V signal to 163mV. The difference is only 1dB which is not noticeable. Why a transformer? Why not two resistors instead? __________________ Uncle $crooge

15th April 2008, 05:40 PM	(permalink)
Blue Dog	Thanks for confirming my suspicions and for knowing/doing the math I think the matching transformer is being used to eliminate any potential ground loop hum on the signal and more importantly, to reduce the risk of any damage to the computer or radio from any difference in voltage potential - guess it does double duty by acting as an isloation transformer as well as doing the match.