Althenick
I was led to believe by a Pilot (Ok not FAA - but he told me he was a pilot -many times over in fact) that the Jetstream had a Sea King Radar in it which I took to be of the MK6 variety and therefore I thought it may be of some use.
I don’t know if the Mk2 was eventually upgraded, but Tourist’s post implies the Mk2 was/is still fitted with EW190, a.k.a. EKCO Weather Radar, MEL E190 which is a cloud and clunk beast. It was also fitted, among others, to Andover, Dominie, VC10, Nimrod AEW, Andover Calibration Sqn; and to commercial airliners. (British Caledonian were a major user).
The High Power version of this (EW290) was/is fitted to Nimrod MR1, Hercules and others. Many of the LRUs are common between variants, the main difference being the higher power Transmitter/Receiver.
The link to Sea King is that the Intellectual Property Rights were acquired from EKCO (whose factory was in Southend) by what was MEL (Mullard) in Crawley, who became part of the Philips empire and, in turn, Thorn Radar, Racal Radar and Thales.
The Sea King radars you speak of were MEL products, based on RSRE specifications (that is, if MEL flogged them to anyone else, which they did, we got a cut); whereas the EW series was wholly proprietary, which makes them a very lucrative bread and butter product over the years. However, the first SK version (Lightweight Helicopter Radar, fitted to RN ASW Mk1/2) had much commonality at component level with the EW series, which puts your friend on the right track.
The RAF then fitted this to their SAR Mk3 and, when they required a weather mode, some features of the EW series were incorporated in the LWR design. This programme was cancelled at the production stage, but a handful of weather mode radars were converted.
The RN "replaced" LWR with Sea Searcher, in the Mk5. The obvious difference is the larger, flat topped dorsal radome. But SS retained components of LWR (and, hence, EW) mainly in the display sub-system. SS development was cut short by a year when the Falklands War broke out, so for some years after that what was in-service didn’t align with the spec or pubs, lacking some key features like TWS and sonics interfacing.
When the RAF MK3As were built, they surprisingly specified a hybrid of the old LWR and the newer Super Searcher, a development of SS. In short, lovely processed, colour display, but sod all targets and huge blind arc due to the old low power Tx/Rx and smaller scanner. Nobody knows why, as they were offered, free of charge, the RN’s surplus Tx/Rx etc (as the RN had chopped the Mk6 fleet numbers). The RAF also inherited the RN’s stock of LWR when SS was introduced.
Hope that little potted history explains the links. You weren’t too far away (and I’ve probably got some aspects wrong). EW190 wasn't fitted to SK, but in a design sense is part of the same family of radars.