[SI-LIST] Discussion: What is the extra attenuation if a 50ohm source interfacing a 75ohm cable which terminated with 75ohm?
- From: "Zhenwei Wang (zhenwwan)" <zhenwwan@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 7 Jun 2012 16:41:39 +0800
Hi experts,
Today I have a dicussion with my colleague. The topic is What is
the extra attenuation if a 50ohm source interfacing a 75ohm cable which
terminated with 75ohm resistor? Just like that when using a 75ohm cable
connected to a 50ohm output instrument.
The scenario is:
Source(50ohm resistor)===>PointA===75ohm cable===>PointB
||
||(75ohme resistor)
GND
My opinion: Based neglecting the multi-refection, there will be
refection factor at pointA, which is 0.2. So 80% energy was launched
into 75ohm cable. Then the voltage at pointB is Vin*0.8/2=Vin*0.4. But
it should be 0.5*Vin at pointB. So the extra attenuation is
0.5-0.4=0.1==>-20db.
Am I right?
BR
Zhenwei(Jason) Wang
Cisco Systems (Shanghai) Video Technology Co., Ltd.
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