QO-100 Downlink on RTL-SDR: Receive Setup Guide

| June 4, 2026 | Amateur Radio (Ham Radio) | No Comments

Receiving the QO-100 (Es’hail-2) narrowband downlink is a straightforward project, especially since you can repurpose standard satellite TV hardware. The downlink operates at 10.489 GHz (X-band), so the main objective is to downconvert that signal to an Intermediate Frequency (IF) that the RTL-SDR can tune to.

Dish and Feed

  • Satellite Dish: A standard off-the-shelf Ku-band satellite TV offset dish works perfectly. While a 60cm dish is the absolute minimum, an 80cm to 120cm dish is highly recommended. The larger aperture gives you a better signal-to-noise margin, making it much easier to pull weak SSB and CW signals out of the noise floor.
  • The LNB (Low Noise Block): The LNB sits at the focal point of the dish and handles the actual frequency conversion. You cannot use older DRO (Dielectric Resonator Oscillator) LNBs because their local oscillators drift severely with temperature changes. You need a PLL (Phase Locked Loop) LNB.
    • The Bullseye 10 kHz TCXO LNB is currently the gold standard for QO-100. It features a highly stable TCXO that minimizes frequency drift — an absolute requirement for narrow modes like SSB.
    • The LNB uses a 9750 MHz local oscillator. It takes the 10.489 GHz downlink and downconverts it to a 739 MHz IF.

The Receiver Chain

The primary challenge in wiring the receive chain is sending power up the coaxial cable to run the LNB without feeding that same voltage into your RTL-SDR and damaging it.

  • Bias-Tee: You must insert a Bias-Tee inline between the LNB and the SDR. The narrowband transponder on QO-100 is vertically polarized. Standard TV LNBs switch to vertical polarization when fed 12V to 13V DC, so you will inject a 12V supply into the Bias-Tee.
  • RTL-SDR: The RTL-SDR effortlessly tunes to the 739 MHz IF coming out of the Bias-Tee. The RTL-SDR Blog V3 or V4 models are ideal because their internal 1 PPM TCXOs prevent additional drift inside the receiver itself.
  • Cabling: Standard 75-ohm RG6 satellite coax is run from the LNB to the Bias-Tee. You will need F-connectors on the coax run and SMA adapters to mate with the Bias-Tee and RTL-SDR.

Software Alignment

Even when using a high-quality TCXO LNB, slight thermal drift is unavoidable at 10 GHz. The most elegant way to handle this is in the digital domain.

SDR Console (V3) is the preferred SDR software for QO-100 operators. It features a built-in “Geostationary Beacon” locking function. QO-100 continuously transmits a PSK telemetry beacon at the bottom edge of the band (10,489.550 MHz). By instructing SDR Console to lock onto this beacon, the software dynamically adjusts the VFO to keep the entire passband perfectly stable, entirely erasing any residual drift from the LNB.