Another What's This?

Carnaby;31140 wrote:

Interesting and useful chart Stevo (do you have one for Middleton-St_George?).

The Cambridge one shows the ILS localizer just off the end of Rwy05 - frequency 111.3 Mhz.
The Inner Marker should be 1,000 feet off the other end, i.e. Rwy23 - certainly not just in front of the CT.
The plan may not show the IM as they were 'standard' items operating on 75MHz.
The length of the elements in Bill's photo, (2 metre-ish) however suggests something around that frequency.

Hmm :confused:

Does Essex Girl, or EGDGZTCW have a contact there?

Graham

I agree with DS, I'm fairly sure it's not ILS related. Could it be VDF of NDB.
Certainly not MM and definately not OM. I know a chap at Cambridge, I'll give a ring tomorrow see if we can solve this one

Chris

EGDGZTCW;31252 wrote:

I agree with DS, I'm fairly sure it's not ILS related. Could it be VDF of NDB.
Certainly not MM and definately not OM. I know a chap at Cambridge, I'll give a ring tomorrow see if we can solve this one
Chris

That dosen't quite make sense, I believe DS is saying it is ILS related?

The ILS localiser and the antenna for breaking the beam is generaly at the end of one of the runways.

The pictured item certainly dosen't look big enough for NDB.
VDF is the new version of DRDF that I mentioned at the end of my previous post, and I think that is what is denoted on the opposite side of the airfield on the plan.
I'm sure it is an old RDF.

mawganmad;31260 wrote:

That dosen't quite make sense, I believe DS is saying it is ILS related?

No it doesn't make sense, you're right, sorry.......where's me coat?

Just found my slide of the Inner Marker by the side if the A67 at Middleton St George (c.1980) and it looks pretty identical to the Cambridge device. The IMs at Leeming and Church Fenton are also easy to see from the road and I'm sure they were similar.

But the Cambridge one, in its position, certainly isn't an IM. Whatever it is, (assuming that Yagi aerial is upright), it's going to squirt a 90 degree-ish 'fan' at around 75Mhz straight up into the sky.

The search continues.

Graham

Carnaby;31125 wrote:

Bill,
It looks like an Inner Marker beacon for the ILS, but....

a) The IM is normally just outside the airfield - the pic suggests it is too close to the airfield.
b) Why is the antenna at some strange angle. Two possibilities:

• It's fallen over
• It has been configured for mixed polarity.

With the old wartime SBA system the Main Beacon had vertical aerial elements, and the aircraft had a vertical aerial to receive this. The SBA Inner and Outer markers had horizontal elements, and the aircraft was equipped with a horizontal rod antenna - often described as a 'handrail'.

Then along came VHF BA for using in single-seat fighters, using only the aircraft's R/T set. The aircraft R/T aerial was a vertical element and was therefore insensitive to horizontally-polarised marker beacons. They didn't want to add an extra horizontal aerial to the fighter, so the solution was to move the ground marker beacons well to the side of the runway centre-line axis, and angle their antennas accordingly. An angle of 45 degrees would be optimal. A far from ideal solution but necessary at the time.

Having said all that Option 1 above seems likely.

Where is the device physically located?

Graham

(I do like these 'What is this?' threads)

Hi carnaby, I suspect the antenna is a later addition but the building could have been CADF, the forerunner of DRDF. CADF was before my time I'm afraid so not sure what the ae array looked like but I think I've seen a picture of DRDF complete with array elsewhere on one of the threads, will have a mosey and try find it again.

Found the picture of DRDF on REF'S Swinderby site, airfield navigation beacon 01/02, wish I'd had the gumption to photo the interiors of these buildings when I was in, as well as the exteriors!!:|doh

cbrjock;31506 wrote:

Hi carnaby, I suspect the antenna is a later addition but the building could have been CADF, the forerunner of DRDF.

Thats what I'm saying, though I called it (probably incorrectly) RDF.

Not sure why people are still suggesting ILS kit, this dosen't appear in the middle of an airfield!

mawganmad;31632 wrote:

Not sure why people are still suggesting ILS kit, this dosen't appear in the middle of an airfield!

I wasn't aware any one still was.

Regarding CADF - the web tells me this stands for:

• Commutated Antenna / Aerial Direction Finder
• Communications and Acquisition Direction Finding
• Cathode-ray tube automatic direction finding

I suspect we are talking about the first one. I then found this comment after a Google search.

A new direction finder working on this band was eventually produced, known as CADF (commutated aerial D/F). A brick building with a 20ft diameter metal mesh disc on its roof appeared on all airfields.

This source has got to be 100% correct as I discovered the author was NP no less . Link here

What is strange about the building is that its four obstruction lights are mounted at roof level. Hence they would be below any aerial structure mounted on its top. Perhaps it wasn't a radio / radar facility at all?

Graham