Alex Pettit conducted some investigations and posted the results on SARA Mailing List 20/1/2026.
Alex made the followong conclusions. Please note that correct length of the feed does depend on the design of the dish, so the following will not be true of other dish focal ratios.
The dipole on the Nooelec 1.4GHz feed appears to be positioned beyond the ideal Focal Point of a 1m f/D 0.35 dish is 35cm (with a small variation from that depending on feed design). This may be because it was designed to cover a wide frequency range.
Alex has recommended trying positioning the mid point of the black enclosure ( location of the dipole ) at 29cm from the dish or considering upgrading to the Kraken Discovery Dish Feed & LNA.
This is the same as ensuring that the flat apex of the inverted V reflector element is placed 33cm from the surface of the same side of the dish as the reflector element.
https://github.com/AP-HLine-3D/HLine3D/blob/main/21cm_Step1b_KrakenDiscoveryFeed_Eval_05.pdf