UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Help with FM tuner Signal injection/probing

djsbriscoe · 25th Apr 2019, 9:47 am

Hi,
Does anyone have any tips on how I should inject signals into and probe for signals in an FM tuner?
For instance how would I correctly inject a 100 MHz 100uV (-67dBm) RF signal from a signal generator (Marconi 2022E 50 ohm output impedance) into a 75 ohm antenna input? Is it best to set the input impedance of the oscilloscope (which I'm using to measure this input voltage) to 50 ohms or 1 Meg Ohm? What kind of loading effects can I expect.
Also, what is the best way of probing the Circuits in the tuner without introducing any significant loading. Likewise, what is the best way of injecting signals? I ask these seemingly simple questions as I am not experienced in aligning receivers and I want to learn. Hope someone can help. Thanks.

PS I'm using standard 75 ohm BNC connectors and coaxial cable. What effect will this have on my measurements.

25th Apr 2019, 9:47 am	#1
djsbriscoe Pentode Join Date: May 2015 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 133	Help with FM tuner Signal injection/probing Hi, Does anyone have any tips on how I should inject signals into and probe for signals in an FM tuner? For instance how would I correctly inject a 100 MHz 100uV (-67dBm) RF signal from a signal generator (Marconi 2022E 50 ohm output impedance) into a 75 ohm antenna input? Is it best to set the input impedance of the oscilloscope (which I'm using to measure this input voltage) to 50 ohms or 1 Meg Ohm? What kind of loading effects can I expect. Also, what is the best way of probing the Circuits in the tuner without introducing any significant loading. Likewise, what is the best way of injecting signals? I ask these seemingly simple questions as I am not experienced in aligning receivers and I want to learn. Hope someone can help. Thanks. PS I'm using standard 75 ohm BNC connectors and coaxial cable. What effect will this have on my measurements.