DeltaRex on a 65-Meter Rooftop: Turning a Loop into a DX Weapon
When the DeltaRex is installed 65 meters above ground level, it becomes much more than a compact multiband loop. At this altitude, the DeltaRex exhibits significantly enhanced low-angle performance, making it one of the most efficient urban DX antennas available.
Operating Bands and Modes
| Band | Functionality | Notes |
|---|---|---|
| 10m | ✅ DX | Efficient, low-angle radiation |
| 12m | ✅ DX | Strong performance |
| 15m | ✅ DX | Slight multi-lobe pattern |
| 17m | ✅ DX | Good radiation, wide match |
| 20m | ✅ DX | Full-wave loop, strong DX |
| 30m | ✅ DX/NVIS | Mixed pattern, tunable |
| 40m | ✅ DX/NVIS | Low-angle performance from height |
| 60m | ⚠ NVIS | Usable with tuner, high-angle pattern |
| 80m | ⚠ NVIS | Sub-resonant, low efficiency |
| 160m | ❌ Not supported | Too short for practical use |
Radiation Angles at 65m Rooftop Mounting
| Band | Est. Elevation Angle |
|---|---|
| 10m | ~6° |
| 12m | ~7° |
| 15m | ~8° |
| 17m | ~10° |
| 20m | ~12° |
| 30m | ~18° |
| 40m | ~22° |
| 60m | ~35° |
| 80m | ~45° |
Why This Matters
At 65 meters height, the DeltaRex exhibits the kind of elevation angles normally associated with full-size verticals placed in ideal open terrain. This results in:
- Clear, low-angle radiation for long-distance DX
- Strong suppression of near-field coupling and ground losses
- Clean, symmetrical azimuth patterns, especially with central rooftop placement
Installation Tips
- Use a central mounting mast to preserve pattern symmetry
- Ensure coaxial feedline is well-choked (1:1 choke 4m down the line)
- Avoid placing near metallic structures that could re-radiate or distort pattern
-
⚠️ Guy the arms in two directions! This ensures mechanical stability against strong wind gusts — critical on tall rooftop deployments
Summary
On a 65-meter-high building, the DeltaRex transitions from a compact multiband loop to a serious DX antenna. With low takeoff angles from 40m to 10m, and usable high-angle NVIS coverage on 60m and 80m, it delivers real performance in places where radials and large installations aren't practical.
DeltaRex on a rooftop: compact. elevated. unleashed.
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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.