GEC (for GPO) 27A Receiver/Measuring Set - Anyone know about these? - UK Vintage Radio Repair and Restoration Discussion Forum

Toothy Chris · 27th Apr 2016, 2:32 pm

Forgive me colleagues, for it is many many years since my last post...

Many years ago I bought a 'GEC 27A Radio Receiver' (MW and LW), which was designed for the then GPO. Reading the instructions in the lid, it was used to detect/measure electrostatic and electromagnetic radiation, on the MW and LW bands.

Looking on-line I have only found one reference to one of these, but the details seems a bit vague:

http://www.radiomuseum.org/r/gec_gpo...eiver_27a.html

I would be interested to hear from anyone who may be able to supply a bit more information about when these were made, how many might have been made (I am guessing not many), and exactly what they were used for.

In addition to being able to receive MW and LW stations, it also has a built in oscillator, covering the same frequencies, although the purpose of this is not clear, as it does not seem to have an o/p - it just seems to go 'over the top' of the received station/signal.

As you can see from the attached photo, this one was last calibrated in 1980, so I guess it was decommissioned shortly after that. I have not found anything to date it, but I'm guessing late 50s or early 60s

Many thanks,

Toothy Chris

dseymo1 · 2nd May 2016, 9:49 pm

Something to do with investigating interference, perhaps?

Radio Wrangler · 3rd May 2016, 8:38 am

It's an interference chasing set. The sort of thing brought along by someone sent out to investigate a complaint of interference.

The oscillator is used to establish a beat with any unmodulated carrier found, because otherwise on an AM set they are silent, and sometimes you can hear some identifiable characteristics brought out this way.

Later equipment like the 40A set (made by Eddystone) had wider coverage and an array of internal ferrite rods, and a step attenuator set for much more serious measurement of levels.

David

Toothy Chris · 14th Jun 2016, 10:11 pm

Thanks David,

I found out from an old colleague, that this very much resembled the later PI FIM - 22/41 which was used by the DTI/Home Office/Radio Authority/Ofcom, to measure field strength, and as you say, to locate the sources of interference. Your comment about the unmodulated AM signals makes perfect sense, and I can now see why the internal oscillator would be required.

Ironically, my colleague and I were both involved in student radio stations, which were then only on MW, and where the electromagnetic signal (it was broadcast using inductive loop aerials) had to be below a certain threshold at the site boundry. So one of these GEC devices could have been used to ensure compliance with that restriction, in the early days of student broadcasting, in the mid 70s.

Chris

27th Apr 2016, 2:32 pm	#1
Toothy Chris Triode Join Date: Jan 2009 Location: West Sussex, UK. Posts: 16	GEC (for GPO) 27A Receiver/Measuring Set - Anyone know about these? Forgive me colleagues, for it is many many years since my last post... Many years ago I bought a 'GEC 27A Radio Receiver' (MW and LW), which was designed for the then GPO. Reading the instructions in the lid, it was used to detect/measure electrostatic and electromagnetic radiation, on the MW and LW bands. Looking on-line I have only found one reference to one of these, but the details seems a bit vague: http://www.radiomuseum.org/r/gec_gpo...eiver_27a.html I would be interested to hear from anyone who may be able to supply a bit more information about when these were made, how many might have been made (I am guessing not many), and exactly what they were used for. In addition to being able to receive MW and LW stations, it also has a built in oscillator, covering the same frequencies, although the purpose of this is not clear, as it does not seem to have an o/p - it just seems to go 'over the top' of the received station/signal. As you can see from the attached photo, this one was last calibrated in 1980, so I guess it was decommissioned shortly after that. I have not found anything to date it, but I'm guessing late 50s or early 60s Many thanks, Toothy Chris Attached Thumbnails

2nd May 2016, 9:49 pm	#2
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: GEC (for GPO) 27A Receiver/Measuring Set - Anyone know about these? Something to do with investigating interference, perhaps?

3rd May 2016, 8:38 am	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: GEC (for GPO) 27A Receiver/Measuring Set - Anyone know about these? It's an interference chasing set. The sort of thing brought along by someone sent out to investigate a complaint of interference. The oscillator is used to establish a beat with any unmodulated carrier found, because otherwise on an AM set they are silent, and sometimes you can hear some identifiable characteristics brought out this way. Later equipment like the 40A set (made by Eddystone) had wider coverage and an array of internal ferrite rods, and a step attenuator set for much more serious measurement of levels. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

14th Jun 2016, 10:11 pm	#4
Toothy Chris Triode Join Date: Jan 2009 Location: West Sussex, UK. Posts: 16	Re: GEC (for GPO) 27A Receiver/Measuring Set - Anyone know about these? Thanks David, I found out from an old colleague, that this very much resembled the later PI FIM - 22/41 which was used by the DTI/Home Office/Radio Authority/Ofcom, to measure field strength, and as you say, to locate the sources of interference. Your comment about the unmodulated AM signals makes perfect sense, and I can now see why the internal oscillator would be required. Ironically, my colleague and I were both involved in student radio stations, which were then only on MW, and where the electromagnetic signal (it was broadcast using inductive loop aerials) had to be below a certain threshold at the site boundry. So one of these GEC devices could have been used to ensure compliance with that restriction, in the early days of student broadcasting, in the mid 70s. Chris Last edited by Toothy Chris; 14th Jun 2016 at 10:19 pm.