¶ Analog FM Transmission Over FR3
Transmit an analog FM signal end-to-end over FR3 (millimeter-wave) bands using a USRP-2974 (Krypton) paired with Pi-Radio FR3 front-ends, then receive and demodulate it on a second USRP-2974 — all orchestrated from GNU Radio flowgraphs.
¶ Overview
This tutorial demonstrates an analog FM transmission path that spans the FR3 spectrum. A GNU Radio FM transmitter flowgraph runs on a USRP-2974 (Krypton) and outputs an IF signal at 1.5 GHz. A Pi-Radio FR3 front-end up-converts this to 10 GHz for over-the-air transmission via Vivaldi antennas. On the receive side, a second Pi-Radio front-end down-converts the 10 GHz signal back to 1.5 GHz, where a second USRP-2974 runs a GNU Radio FM receiver flowgraph to recover the audio baseband.
The Pi-Radio web UI (port 5006 on the rfdev-* nodes) is used to configure the LO frequencies for each front-end. This experiment exercises the full FR3 hardware stack in COSMOS Sandbox 1 and serves as the entry point for all subsequent FR3 tutorials.
¶ Learning outcomes
After completing this tutorial you will be able to:
- Configure Pi-Radio FR3 front-ends via the web UI (LO frequency panel).
- Run a GNU Radio FM transmitter flowgraph on a USRP-2974 (Krypton).
- Run a GNU Radio FM receiver flowgraph on a second USRP-2974.
- Verify an end-to-end FR3 analog link at ~10 GHz.
¶ At a glance
| Difficulty | Intermediate |
| Estimated time | TODO: verify |
| Domain / sandbox | sb1.cosmos-lab.org |
| Topic group | FR3 |
| Last verified | Not re-tested (migrated 2026-06-20) |
¶ Prerequisites
Background knowledge
- Familiarity with the USRP-2974 (Krypton): embedded X310, 10 MHz–6 GHz, 160 MHz BW.
- Basic GNU Radio flowgraph operation.
- FR3 hardware overview — see the FR3 hardware pages on this wiki.
Account & access
- A COSMOS account — register here.
- An approved reservation on sb1.cosmos-lab.org with FR3 hardware access — see Make a reservation.
- SSH access to the domain console — see SSH access.
- Browser access to the Pi-Radio web UI on the rfdev-* nodes (port 5006).
¶ Resources required
Devices / nodes
| Resource | Role | Qty | Notes |
|---|---|---|---|
| sdr1-piradio | FM transmitter (USRP-2974 / Krypton) | 1 | Runs GNU Radio FM TX flowgraph; IF output at 1.5 GHz |
| sdr2-piradio | FM receiver (USRP-2974 / Krypton) | 1 | Runs GNU Radio FM RX flowgraph; IF input at 1.5 GHz |
| rfdev-sdr1-piradio | Tx Pi-Radio FR3 front-end | 1 | Up-converts 1.5 GHz IF → ~10 GHz RF; configured via web UI port 5006 |
| rfdev-sdr2-piradio | Rx Pi-Radio FR3 front-end | 1 | Down-converts ~10 GHz RF → 1.5 GHz IF; configured via web UI port 5006 |
Disk images
| Image | Load onto | Provides |
|---|---|---|
| fr3-tutorials.ndz | sdr1-piradio, sdr2-piradio | GNU Radio FM TX/RX flowgraphs + UHD for USRP-2974 |
Software components
| Component | Version | Source |
|---|---|---|
| GNU Radio | TODO: verify | preinstalled in fr3-tutorials.ndz |
| UHD (USRP Hardware Driver) | TODO: verify | preinstalled in fr3-tutorials.ndz |
| Pi-Radio web UI | TODO: verify | embedded in rfdev-* nodes (port 5006) |
Spectrum / RF / special
- 2× Vivaldi antennas (Tx and Rx) connected to the Pi-Radio FR3 front-ends. See the FR3 hardware pages for antenna layout.
- Example RF frequency: ~10 GHz (High LO = 10 GHz, Low LO = 1.5 GHz IF). Exact placement depends on mixer sign/path; verify with your reservation's allowed spectrum.
¶ Topology
Two USRP-2974 (Krypton) nodes each paired with a Pi-Radio FR3 front-end. The control plane uses the standard COSMOS console; the RF path is: USRP-2974 (sdr1) → Pi-Radio FR3 Tx (rfdev-sdr1) → Vivaldi Tx antenna → over-the-air at ~10 GHz → Vivaldi Rx antenna → Pi-Radio FR3 Rx (rfdev-sdr2) → USRP-2974 (sdr2). The Pi-Radio web UI for each rfdev is accessible via a browser from the console or a forwarded port.
¶ Setup
- Reserve sb1.cosmos-lab.org with FR3 resources and log into the console:
ssh <username>@console.sb1.cosmos-lab.org - Turn all resources off before imaging:
omf tell -a offh -t system:topo:allres - Load the FR3 tutorials image onto the USRP nodes:
omf load -i fr3-tutorials.ndz -t sdr1-piradio,sdr2-piradio - Turn the nodes on and confirm they are up:
omf tell -a on -t sdr1-piradio,sdr2-piradio omf stat -t sdr1-piradio,sdr2-piradio - Complete the FR3 hardware setup steps (shared procedure) — see the FR3 Setup guide.
¶ Instructions
¶ Step 1 — Configure the Pi-Radio FR3 front-ends
Open a browser and navigate to the Pi-Radio web UI on each rfdev node at port 5006.
For the Tx front-end (rfdev-sdr1-piradio), open the Frequency panel and set:
- Low LO Frequency (GHz):
1.500000 - High LO Frequency (GHz):
10.000000
For the Rx front-end (rfdev-sdr2-piradio), open the Frequency panel and set:
- Low LO Frequency (GHz):
1.500000 - High LO Frequency (GHz):
10.000000
This 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 approximately 10 GHz, and back to 1.5 GHz on the receive path. Exact placement depends on mixer sign and path; 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.
¶ Step 2 — Run the GNU Radio FM transmitter
SSH from the console to the transmitter node:
ssh root@sdr1-piradio
Launch the GNU Radio FM transmitter flowgraph (example path — verify against the image):
root@sdr1-piradio:~# gnuradio-companion grc-fm-tx.grc
The flowgraph generates an FM-modulated signal at 1.5 GHz IF, which is fed to the Pi-Radio Tx front-end for up-conversion to ~10 GHz.
¶ Step 3 — Run the GNU Radio FM receiver
Open a second SSH session from the console to the receiver node:
ssh root@sdr2-piradio
Launch the GNU Radio FM receiver flowgraph (example path — verify against the image):
root@sdr2-piradio:~# gnuradio-companion grc-fm-rx.grc
The flowgraph receives the 1.5 GHz IF from the Pi-Radio Rx front-end and FM-demodulates it to recover the audio baseband.
¶ Verification
- The Pi-Radio web UI on both rfdev nodes shows the LO frequencies locked at 1.5 GHz (Low) and 10 GHz (High).
- The GNU Radio FM transmitter flowgraph runs without errors on sdr1-piradio.
- The GNU Radio FM receiver flowgraph on sdr2-piradio shows a received signal and demodulated audio output.
¶ Cleanup
omf tell -a offh -t system:topo:allres
(No omf save needed unless you modified the image.)
¶ Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
| Pi-Radio web UI not reachable at port 5006 | Network routing or rfdev node not booted | Verify the rfdev-* node is powered and reachable from the console; check port forwarding if accessing from outside the sandbox |
| GNU Radio flowgraph fails to start | UHD device not found or wrong IP | Confirm sdr1-piradio/sdr2-piradio are booted with fr3-tutorials.ndz and the USRP-2974 is accessible via UHD |
| No signal at receiver | LO frequencies mismatched between Tx and Rx Pi-Radio front-ends | Verify both rfdev nodes have identical Low LO (1.500000 GHz) and High LO (10.000000 GHz) settings |
| Weak or noisy received signal | Antenna alignment or gain settings | Check Vivaldi antenna orientation per FR3 hardware page; adjust gain in the Pi-Radio web UI |
¶ References
- Pi-Radio website
- GNU Radio
- FR3 hardware pages
- FR3 Setup guide
- Available SDR hardware
- Make a reservation
- SSH access
Author(s): COSMOS team · Last verified: Not re-tested (migrated 2026-06-20) · Tested image/release: fr3-tutorials.ndz · Tags: fr3, sdr, gnuradio, fm, pi-radio, usrp-2974, krypton, millimeter-wave