For 1420 MHz work, the advantage of a professionally manufactured WR-650 waveguide is usually much smaller than many people expect.
Electrical performance
A commercial WR-650 section will have:
- Precisely controlled internal dimensions.
- Very straight walls and accurate flanges.
- Low surface roughness.
- Predictable impedance and mode behaviour.
- Published specifications for insertion loss and VSWR.
At 1420 MHz, however, waveguide losses are already extremely low. For a short feed section on a radio telescope, the difference between a well-made homemade guide and a professional one may only be a few hundredths of a dB.
For example:
- Professional aluminium WR-650: perhaps 0.01-0.03 dB loss over a short feed section.
- Carefully built homemade guide: perhaps 0.03-0.10 dB loss.
In a hydrogen-line receiver system with a typical sky temperature and LNA, this difference is often undetectable.
What matters much more
For radio astronomy, these factors usually dominate performance:
- Feed probe design.
- Probe position.
- LNA noise figure.
- LNA placement directly at the feed.
- Spillover losses.
- Dish illumination efficiency.
A poorly designed probe in a perfect WR-650 can easily lose more signal than a homemade waveguide with an optimized probe.
Mechanical advantages
Professional WR-650 does have significant practical benefits:
- Weatherproof flanges.
- Better structural rigidity.
- Easy connection of standard components.
- Known dimensions for simulations.
- Long-term stability.
If you are repeatedly modifying feeds or doing interferometry where repeatability matters, these benefits can be valuable.
Homemade waveguide performance
Many amateur hydrogen-line observers have successfully used:
- Folded aluminium sheet.
- Galvanized steel ducting.
- Aluminium flashing.
- Plywood boxes lined with metal.
A homemade WR-650 can perform extremely well if:
- Internal dimensions are within a few millimetres of specification.
- Corners are electrically continuous.
- The probe dimensions and position are optimized.
- The structure remains mechanically stable.
At 1420 MHz, wavelength is about 21 cm, so the tolerances are relatively forgiving compared with microwave systems at 10 GHz or above.
For your radio telescope
Given your interest in 1420 MHz hydrogen-line observations, I would spend money on:
- A lower-noise LNA.
- Better feed optimization.
- More integration time.
- Better RFI mitigation.
before spending hundreds of pounds on commercial WR-650.
A carefully constructed homemade WR-650 feed can achieve well over 95% of the practical performance of a professional waveguide section for amateur hydrogen-line work. The biggest gains usually come from optimizing the feed geometry rather than from the waveguide itself.