Hi All

Does anyone have actual experience of using SBA or have a good training manual for it?

I am restoring an SBA system to working order and I can't find an explanation of why there is a GLIDE-COURSE switch. I know that in the course setting there is automatic gain control for the main receiver so in theory the Course/Glide indicators would have a constant reading, however when set to GLIDE the pilot can then control the gain of the receiver - but why? How? I surmise that the signal strength would change as the A/C approached the transmitter and so it would be handy if the indication was turned down as the signal got stronger - but on GLIDE what would the Pilot have done? Why?

The SBA I'm referring to is the one where there are just two 'beams', not the 4 quadrant one or ILS, etc.

Incidentally, there was only ever one transmitter on the ground in that system - when you see pictures of it it is clearly a large and expensive item so having more than one would have been a commercial issue. The clever part is that the single transmitter aerial was flanked on either side by identical - but unpowered aerials. Basically these were each just a single wire with a break in the centre.  These were short circuited by a rotary switch driven by a motor such that one was short circuited for the 'DASH' and the other for the 'DOT', The short circuited aerials changed the radiation pattern of the powered aerial from basically a circle into a kidney shape pointing out at right angles to the landing strip. The shape of each DOT and DASH kidney overlapped and gave you the 'constant beam. So in fact the radiated fields were never 'narrow', they were fat, it is the overlap that was narrow.

You can see this 'distortion' of the radio field in a more common use by looking at any of the old TV aerials - the long pointy ones with many cross wires that get smaller towards the end. None of those cross wires are connected to the aerial itself - what they do is to distort the pickup pattern of what would be a circular reception into a long thin lobe/finger that is very much more sensitive and directional. These types then would need 'pointing' at the TV transmitter, which is what you see them doing (OK did see them doing, they have long since been made obsolete!

 Incidentally, I'm going to post this request on another forum as I'd like to reach as wide an audience as possible - I know that this annoys some people - but I can't think why.

Cheers

James

-- Edited by jamesinnewcastle on Tuesday 16th of August 2016 06:52:59 AM

-- Edited by jamesinnewcastle on Tuesday 16th of August 2016 06:58:29 AM