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Hi,
My question is simple -- if I want to connect a spectrum analyser (SA) to the output of a transmitting WARPv2 board, do I need to use attenuation as this should not harm the SA too much as it can accept a wide range of powers (50 Ohm matched impedance has been applied)?
If an attenuator is not used in such a set-up, what are the consequences?
I used the following commands in Matlab
wl_interfaceCmd(nodes,RFA,'tx_gains',3,63);
wl_interfaceCmd(nodes,RFB,'tx_gains',3,63);
to drive my WARP v2 Tx node (the max. power settings) and the power I get at the SA, integrated over a bandwidth of 24 MHz (2 x 12 MHz cut-off freq.) is around -38 dBm. The board spec says it can deliver 18 dBm. Is there a chance that something is damaged?
Cheers,
Pat
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Your analyzer should have a label near its input stating its max power. The benchtop analyzers I've used have been tolerant of 1W. Connecting the WARP RF interface directly to a 1W-tolerant input is fine. The WARP RF interface is AC-coupled at the SMA connector, so it's safe to connect directly to an input that requires 0 VDC (also common for analyzers).
If your analyzer's limit is lower, or not stated, using external attenuation is a good idea. Most analyzers have a way to specify what external attenuation is being used and adjust their power measurements accordingly.
to drive my WARP v2 Tx node (the max. power settings) and the power I get at the SA, integrated over a bandwidth of 24 MHz (2 x 12 MHz cut-off freq.) is around -38 dBm. The board spec says it can deliver 18 dBm. Is there a chance that something is damaged?
It depends on what waveform you're transmitting. The most basic test is to transmit a continuous sinusoid (use WARPLab's continuous Tx mode) and measure its power with a cursor on the analyzer. This should be ~18dBm for a sinusoid ~5MHz offset from the carrier frequency for 2.4GHz channels.
Also, keep in mind many analyzers don't implement time gating, so if you measure a signal with duty cycle <100%, the power measurement might include some zero-power time. WARPLab's continuous Tx mode is useful here.
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