RFI Mapping

At low elevation angles, the dish points toward the horizon — straight into the terrestrial radio environment. Microwave backhaul links, weather radar, spurious emissions from industrial equipment, and even LED lighting can produce Ku-band interference that shows up as elevated RSSI readings. By sweeping the full azimuth range near the firmware’s elevation floor, you build a 360-degree interference map of your site.

This is useful for three reasons. First, it documents which azimuths are contaminated by terrestrial emitters, so you can avoid those directions during sky observations. Second, it establishes a baseline that makes it possible to detect new interference sources when they appear. Third, it’s just interesting to see what’s transmitting at 10-12 GHz in your neighborhood.

What you’ll measure

• RSSI versus azimuth at one or more low elevation angles, producing a polar interference map
• Elevation falloff — how quickly interference diminishes as you tilt away from the horizon
• Time-of-day variation — intermittent emitters (automotive radar, industrial processes) that only appear at certain hours

Terrestrial interference typically produces sharp, narrow RSSI peaks at specific azimuths — much narrower than the broad rises seen from satellites, because the sources are relatively close and the dish beam is tight. A cell tower’s microwave backhaul link, for example, appears as a spike 1-3 degrees wide at the tower’s bearing.

Prerequisites

• Motors homed and calibrated (see Calibration & Homing)
• TV search disabled (see Disabling TV Search)
• LNA enabled (dvb > lnbdc odu)
• Serial output logged to a file
• Clear sightlines — no obstructions within 32.5 inches of the dish base that could shadow the beam at low elevation

Elevation floor

The Carryout G2 firmware enforces a minimum elevation of 18 degrees (NVS index 101). You cannot point below this angle with standard motor commands. At 18 degrees, you’re looking at objects roughly 3x the dish’s ground-level height above the horizon at a distance of 100 meters. This is low enough to pick up most terrestrial emitters within line of sight.

Procedure

1. Home the motors and set minimum elevation.

   TRK> mot
   MOT> h 0
   MOT> h 1
   MOT> a 1 18

   Start at the firmware floor (18 degrees) for maximum terrestrial sensitivity.

2. Enable the LNA.

   MOT> q
   TRK> dvb
   DVB> lnbdc odu
   DVB> q
   TRK> mot

3. Run the first sweep. Use azscan for a quick RSSI-only survey, or azscanwxp for transponder-cycling data.

   For a fast survey:

   MOT> azscan 360 0 100

   For detailed data with lock detection:

   MOT> azscanwxp 0 360 100 8

   Using fewer transponders (8 instead of 32) speeds up the sweep. For RFI mapping, RSSI matters more than lock status — terrestrial emitters rarely produce valid DVB carriers.

4. Repeat at higher elevations. Increase elevation in 2-degree steps to measure how interference falls off with angle.

   MOT> a 1 20
   MOT> azscan 360 0 100
   MOT> a 1 22
   MOT> azscan 360 0 100
   MOT> a 1 25
   MOT> azscan 360 0 100

   Most terrestrial interference drops sharply between 18 and 25 degrees. The rate of falloff tells you whether the source is nearby (steep falloff) or distant (gradual falloff).

5. Check dual polarization. Some terrestrial emitters are polarized. Run the 18-degree sweep in both H-pol (18V, boot default) and V-pol (13V via lnbdc odu).

   MOT> a 1 18
   MOT> azscanwxp 0 360 100 8

   Compare H-pol and V-pol RSSI at each azimuth. A source that appears in only one polarization is a linearly polarized emitter — consistent with microwave backhaul antennas, which are typically single-polarization.

6. Time-of-day comparison. For a thorough site survey, run the 18-degree sweep at different times:

   • Early morning (05:00-06:00) — minimal human activity, automotive radar quiet
   • Midday (12:00-13:00) — peak industrial and commercial activity
   • Evening (20:00-21:00) — residential electronics, LED lighting harmonics
   • Late night (02:00-03:00) — quietest baseline

Interpreting results

Plot RSSI versus azimuth for each elevation angle. Terrestrial interference shows these characteristics:

Pattern	Likely source
Sharp peak (1-3 deg wide), constant across time	Fixed microwave backhaul link or point-to-point relay
Sharp peak, appears only during certain hours	Intermittent emitter (automotive radar, industrial process)
Broad rise (10-20 deg wide) at low EL, absent at 25 deg	Urban RF clutter — aggregate of many weak sources at the horizon
Peak that shifts azimuth between sweeps	Moving source (vehicle radar) or multipath reflection
Peak present in H-pol only, absent in V-pol	Linearly polarized fixed emitter (backhaul antenna)
Peak present in both polarizations	Unpolarized or circularly polarized source

RSSI scale for terrestrial sources:

RSSI range	Interpretation
489-520	Normal noise floor with LNA, no detectable interference
520-600	Marginal — may or may not affect sky observations at this azimuth
600-800	Moderate interference — will degrade weak-signal DVB measurements
800+	Strong interference — avoid this azimuth for sky work

FCC license lookup

If you identify a strong, persistent interference source at a specific bearing, you can correlate it with FCC license data. The FCC Universal Licensing System lists licensed microwave links with their coordinates and frequencies. Convert your azimuth to a geographic bearing, draw a line on a map, and see what’s there. Many 10-12 GHz emitters are licensed fixed-service microwave links between cell towers.

Common Ku-band terrestrial emitters

Understanding what generates Ku-band interference helps you classify what you find:

Source type	Frequency range	Characteristics
Fixed-service microwave links	10.7-11.7 GHz	Narrow beam, fixed bearing, 24/7, single polarization
Weather radar (X-band spillover)	9.3-9.5 GHz harmonics	Pulsed, rotating (bearing shifts each sweep), broadband
Automotive radar (77 GHz subharmonics)	Sporadic	Appears as brief spikes at road-facing azimuths, inconsistent timing
Industrial ISM equipment	10.525 GHz	Motion sensors, door openers — weak, very short range
Satellite uplink earth stations	14.0-14.5 GHz	Strong, fixed bearing, directional — may appear as ground reflection off nearby structures
LED driver harmonics	Broadband	Very weak, correlates with lights-on hours, from switching power supplies

Most persistent interference at Ku-band comes from licensed fixed-service microwave links. These are point-to-point connections between cell towers, data centers, and broadcast facilities, typically transmitting at 10-100 mW into high-gain dishes. They produce the sharpest, most consistent RSSI peaks in your survey.

Building an RFI database

For ongoing site monitoring, save each sweep with metadata:

# Filename convention
rfi_<date>_<time>_EL<deg>_<pol>.log

# Example
rfi_2026-02-16_0600_EL18_Hpol.log
rfi_2026-02-16_0600_EL18_Vpol.log
rfi_2026-02-16_1200_EL18_Hpol.log

Over weeks and months, this database reveals seasonal patterns (foliage blocking/unblocking microwave paths), new emitter deployments, and the overall interference trend at your site. If you’re planning extended sky observation campaigns, this data tells you which azimuths are safe and which hours are quietest.

Elevation falloff analysis

The multi-elevation sweep data reveals source distances. Plot RSSI versus elevation for each interference peak. The rate at which a source fades as you tilt upward depends on how far away it is and how directional it is:

• Nearby source (< 1 km): RSSI drops rapidly between 18 and 22 degrees as the dish beam lifts above the source
• Distant source (5-20 km): RSSI decreases gradually, still detectable at 25 degrees or higher — the source is far enough away that even at higher elevation the dish beam still clips it
• Reflected/scattered source: Broad, low-level rise that doesn’t fall off cleanly with elevation — the signal is arriving from multiple directions via reflections off buildings or terrain

If a source persists above 30 degrees elevation, it may actually be a geostationary satellite rather than a terrestrial emitter. Cross-reference with the Geostationary Census to confirm.

Going further

• Correlate with weather — atmospheric ducting during temperature inversions can bend distant microwave links into your beam. An interference source that appears only on certain weather conditions is likely a ducted signal from beyond the normal horizon.
• Frequency discrimination — run sweeps with different transponder selections to see if interference is broadband (present across all transponders) or narrowband (affects only specific frequencies). This helps classify the emitter type.
• Combine with the Geostationary Census — overlay your RFI map on the satellite detection map to identify which satellite slots are contaminated by terrestrial interference. Satellites at azimuths with high RFI readings may show artificially elevated RSSI or degraded SNR.
• Site selection — if you’re choosing between multiple locations for a permanent dish installation, run the RFI survey at each candidate site and compare. A site with fewer and weaker interference sources will produce better science data.
• Regulatory reporting — if you identify unlicensed interference that’s degrading satellite reception, the FCC’s Interference Complaint process allows you to file a report. Your RSSI data, bearing, and time logs constitute solid evidence.

Radio Telescope Mode Full guide to the azscanwxp and azscan commands used in these sweeps.

Console Command Reference DVB, MOT, ADC, and PEAK submenu command details.