That helps a lot — Ptarmigan Triffid immediately explains the confusion 👍
You have not used the wrong antenna, only the wrong band name.
Ptarmigan & Triffid (UK Army)
The Ptarmigan system was a modular battlefield trunk communications network used by the British Army from the 1980s onward. It supported multiple radio bearers, not a single band.
TRIFFID specifically was the line-of-sight digital radio bearer, and it operated in L-band, not VHF Band III.
Triffid frequency range
Open technical references and surplus documentation consistently place TRIFFID in the ~1.3–1.5 GHz region, which includes:
- Around 1420 MHz
- Short-range, high-capacity digital battlefield links
- Mast-mounted or vehicle-mounted antennas
- Polarisation often horizontal or configurable
So an antenna from the Ptarmigan Triffid system covering ~1420 MHz is exactly what you’d expect.
Why it sometimes gets called “Band 3”
This is where the confusion comes from:
- “Band 3” in Ptarmigan documentation does NOT mean UK VHF Band III
- It often meant:
- Bearer 3
- Radio Type 3
- Configuration Band 3
- Military systems frequently reuse “band” as an internal system designation, not an RF spectrum definition
Civilian surplus listings then repeat “Band 3” without context.
What your antenna really is
In correct RF terms, your aerial is:
- L-band antenna
- ~21 cm wavelength
- Designed for Ptarmigan Triffid LOS digital links
- Very suitable for 1420 MHz hydrogen-line work
Given your radio astronomy background, this is actually a very nice bit of surplus to have — Triffid hardware was well-engineered, low-loss, and broadband by military standards.