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FM & AM Signal Switching

FM & AM Signal Switching

Hi, everyone.


Good Day.


I have a question about FM & AM Signal Switching.


FM (97.7MHz) or AM (105kHz) signal is generated from my Signal Generator and connected to either FM or AM port of my DUT.


Do I need to use a RF switch to switch between the two port?

Or I can only use a normal General Purpose switch?



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Re: FM & AM Signal Switching



You should be using an RF switch to switch these types of signals (specifically the FM signal). This is due to bandwidth limitations on general purpose switches that would degrade your signal quality.


If your input signal is purely sinusoidal, which the FM and AM signals would be, the bandwidth/insertion loss rating is directly applicable. For example, a switch with a bandwidth rating of 10 MHz implies that the switch has an insertion loss of -3 dB at 10 MHz. If the input signal is a 10 MHz, 1V peak-to-peak sine wave, the output signal will be a 10 MHz, 0.7 V peak-to-peak sine wave. If you were to use a switch with a lower bandwidth, and place a high frequency signal across that switch you would end up with major signal loss through the switch.


I would take a look at RF Switches Above 40Mhz for all available RF switching modules above 40 MHz and select a switch with a bandwidth of at least 100 MHz. Additionally NI PXI Switch Product Selection Guide contain all of the switching modules that we sell and will detail specifications, topologies ect.

National Instruments
Staff Software Project Engineer
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Re: FM & AM Signal Switching

Hi Uoi,


If you're only going to be switching between two channels on one DUT, then the 2594, 2.5 GHz 1x4 multiplexer is the cheapest option.  But I personally highly recommend the 2593, 500 MHz Dual 1x8 (or 1x16) multiplexer because it has a much better cost to channel ratio and easily meets the bandwidth you need.  Using the 2593 would also allow you to easily expand to switch your signal between multple DUTs, up to eight in your case with AM and FM on each.


The 2594 uses SMA connectivity, and the 2593 uses MCX with MCX to SMA/SMB/BNC connectivity available.



Eric S.
AE Specialist | Global Support
National Instruments
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