H/F D/F Stations

[Resmoroh]

Dear All,
Whilst looking for something entirely different I noted some odd-looking RAF D/F Stations (isn't it always the case!!)
One pair were described as "LRCR D/F Station" - at Dyce and St Eval, and the other as "No 6 D/F Station" at Wick. The Dyce/St Eval pair would have a long base-line for good East/West fixes. The Wick station would have a relatively short base-line for fixes with Dyce. If it was No 6 then where were the other 5 - and were there any more?
Were these stations primarily for RAF use?, or were they also part of the wider "Y Service" D/F system?
Any help gratefully received.
Rgds
Peter Davies

[Amrit]

Hi Peter

"No 6 D/F Station" may not actually be a location, indicating another five but actually mean the Marconi No.6 direction finding station which is a type rather than a place.

I don't know anything more about the system as such but it maybe one avenue to explore. I'm just about to pop out and so haven't a chance to do a proper search but this is what I mean:

http://www.mhs.ox.ac.uk/marconi/collection/catalogue.php?invnum=18067&mode=basic

HTH

A

[Resmoroh]

Amrit, Hi,
Thanks for the heads-up on that. However I would be surprised to find that the Marconi No 6 D/F set which was a 1920's animal was still in use 44 years later!! But one never knows!
Having been involved in L/F, H/F, and VHF/UHF D/F-ing I know what the problems are. As I undertsand it H/F D/F was used for the very long ranges (LRCR = Long Range Communications Receive?) well beyond radar ranges (in WW2). In those days H/F propagation conditions forecasting was an art-form rather than a science!!! Perhaps if Ian Brown is on the 'net' he may be able to offer some words of wisdom?
This is a "Wiggly-Amps" problem. Need a Kipper Fleet hairy old Signaller!!
Rgds
Peter Davies

[Dick]

Hi Peter
I trained as an Air Signaller in 1956 and used a D/F station at Wick and one at Manston. By then they had become part of a Civilianised D/F Network for Airline operation and were winding down,but I am sure they were all of war-time origin.From an oldish book "The Challenge of War" by Guy Hartcup it seems that the RAF developed HF/DF as a back-up to the new Radar coming on line in the early 30's(it could have been used to sort out our a/c from the enemy if the Germans didn't co-operate!!) and of course it was useful for SAR.We mustn't forget the use of HF/DF against U-Boats where I am sure that RAF Stations were utilised. It is probably significant that your LRCR Stations are both at Coastal Command airfields, I suspect that CR stands for Cathode Ray indicating a display that gave an instant visual bearing(I'm sure in your Met days you will have seen the AD210 d/f in the Tower for VHF). Such displays were also on ships but the vagaries of HF Radio propagation could mean that a U-boat 40miles from a convoy could be D/F'ed from a shore station 1000 mls away but not heard by the convoy. Perhaps when Amrit gets back he might have a source to develop this further
Regards
Dick

[Resmoroh]

Dick, tks yr input.
With a ex-Kipper Fleet Brass-Pounder (and I've done my bit of that on land - although the W/Ops preferred 'side-swipers'!!) on the net we may be getting somewhere near unravelling this one! Yup, seen the ATC VHF CRT system, and, Yup, noted yr confirmation of the vagaries of H/F propagation conditions. Most of my Mobile Met Unit service (before satellites!) was receiving H/F RTP and Facsimile. If you knew what you were doing you could get something out of apparently nothing but "mush" in the earphones - which is why I referred to the problem being an art-form rather than a science.
Thanks yr help
Peter Davies

[Amrit]

My apologies, Peter, for the (mis)information. That will teach me not to post in a hurry when I was about to go out.

[Andy Fletcher]

HF signals are heavily affected by atmospheric conditions (D & E layers if I remember correctly). The signal can get bounced off the layers and the earth which can result in reception of the signal at very long distances but dead spots (no reception) even very close to the transmitter (skip distance). Nowadays with the use of a Chirp Sounder you can identify the best frequency to use for propogation of a HF signal.

VHF signals and higher are line of sight so their range is limited due to the curvature of the earth.

VLF signals use what is known as ground wave, the signal literally hugs the ground so distance is mainly dependent on transmitter power.

I think the above is more or less correct, it's been a long time since I did comms theory.

Best Regards

Andy Fletcher

[Resmoroh]

Andy, tks yrs,
We always used to use the excuse "Sorry, Boss, but there appears to be a bit of sporadic E about tonight", knowing full well that the 'Boss' had no idea what we were talking about but it sounded technical!!! My experience is well before the days of Chirp Sounders, but they were just coming in as I retired. When asked for a good frequency by the RAF Tac Comms Wing (where the Mobile Met Unit was a part) one would go outside, look at the sun/moon, check the path length from Tx to Rx, check the time of year, check the locations of Tx and Rx, and then say, quite definatively, "I reckon somewhere in the top 7's till midnight, then drop to 5's, and at dawn we'll be lucky if we hear anything below 2's, or above 20's". And this was in the late 50's/60's/early 70's. Bear in mind that aerials (in the field) had to be cut and mounted to cater for all these frequency changes and you'll get some idea of the problem. Art-form - not science. If you want a real problem try working out the best aerial array to receive Darwin, Oz, on Ascension on 22 megs at night in N Hemisphere summer (1982). This was in the Black Buck days!!
Slightly outside the parameters of this Forum, but I'll bet your pension that the same problems were encountered in WW2.
Interesting problems.
Tks yr input
Peter Davies

[Andy Fletcher]

Hi Peter,

Before we got a chirp sounder we would look up the "best" frequencies to use in a comms book (can't remember the official document name) that was usually tucked away on the flight deck. It was supposed to give the optimum frequency of operation depending on time of day and where you were trying to contact, 9 times out of 10 it was no use what so ever for where we were trying to contact but eventually we'd raise someboby somewhere which was good enough for us as we were only testing the system.

Hate to think of the problems associated with HF use during WWII, we at least had the benefit of better technology and supposedly a better understanding of the science involved.

Best Regards

Andy Fletcher

[Chris Scott]

Have enjoyed your anecdotes, Chaps. HF propogation will always be 50 percent art, I guess. Was it the Aerad Supplement that you found in the cockpit, Andy? An A5-sized soft-covered booklet, usually grey. it gave propogation forecasts for "Speedbird London" according to world regions and GMTs. Nowadays, it also includes thumbnail graphs for "Stockholm Radio" and "Portishead Radio" (BT, Somerset).

When overseas and trying to call the UK though, it's often worth running through a spectrum of BBC World Service freqs (UK Tx, not Ascenscion relay Tx), to get an idea of what freq to use. 17705/15070/12095/9410 (kHz) spring to mind, can't remember the lower ones. We pilots don't have a 'chirp sounder ' (what IS that?), but at least it got better when AM was superseded by USB, eventually even for ATC, in the late 1970s.

Just a reminder - to get back towards Peter's topic - that the ionosphere and HF go completely bananas for about 2 hours around sunrise. [For us there was a temptation to get climb clearance early (say, from F/L 370 to F/L 410, if your weight had fallen sufficiently to enable it) because there was no way you would get 2-way with, say, Khartoum ATC during that period.] So it would be useless for DF-ing, just when it might have been needed most desperately in some WW2 operations. And static, of course, goes without saying.