[[Include(/WikiToC)]]

=== Analog FM Transmission Over FR3 ===

This experiment transmits an analog FM signal over the FR3 bands. The FM signal is generated at 1.5 GHz by the USRP-2974 (Krypton), up-converted by a Pi-Radio FR3 front-end and transmitted,in this example, at 10 GHz). A second [https://www.pi-rad.io/ Pi-Radio] front-end down-converts this signal back to 1.5 GHz for a USRP-2974 receiver, that converts it back into analog baseband. The actual modulation and demodulations is done with a GNURadio running on 2974s. Pi-Radio web UI is used to configure the FR3 conversion. 

==== Prerequisites

* COSMOS account and active reservation in Sandbox 1. 
* Familiarity with USRP-2974 (embedded X310, 10 MHz–6 GHz, 160 MHz BW).
* FR3 hardware access (2×[https://www.pi-rad.io/ Pi-Radio] FR3 front-ends) and the fr3-tutorials.ndz disk image for the USRPs.
* [https://www.gnuradio.org/ GNURadio] familiarity

==== Resources required

* Nodes: sdr1-piradio, sdr2-piradio, rfdev-sdr1-piradio, rfdev-sdr2-piradio. 
* Antennas: 2× Vivaldi (Tx/Rx) connected to the Pi-Radio front-ends. (See FR3 hardware pages for antenna layout.) 
* Browser access to Pi-Radio web UI on the rfdev-* nodes (port 5006).

[[Include(/UserGuide/FR3Setup)]]

==== Experiment Execution

Use the Pi-Radio web UI Frequency panel on both rfdev pages (Tx and Rx) and set:

* Low LO Frequency (GHz): 1.500000
* High LO Frequency (GHz): 10.000000

This example pairs a 1.5 GHz IF with a 10 GHz high-side LO (and a 1.5 GHz low-side LO) to place the RF tone at ~10 GHz, and back to 1.5 GHz on the receive path. (Exact placement depends on mixer sign/paths; the screenshot below shows the working settings used in this demo.) Leave Filters, Gain (except where noted), and LO Suppression at defaults for the first run.

GNURadio FM transmitter

[[Image(grc-fm-tx.png, width=1000px)]]

GNURadio FM receiver

[[Image(grc-fm-rx.png, width=1000px)]]

FM transmission

[[Image(fm-tx-rx.png, width=1000px)]]