The locked room mystery by Jakey G3JKY

Strictly speaking, the door wasn’t locked, it was shut tight, but first some background.

The affair occurred in the late 1970s during my time as a laboratory manager at Woolwich Arsenal. Our part of the site was QAD(FVE), Quality Assurance Directorate, Fighting Vehicles and Equipment. My little bit of the QAD was devoted to radio frequency interference tests on their products.  We had two screened rooms of our own, one about the size of a Portacabin, for testing components, and another one to accommodate a whole vehicle. The latter was big enough not just to swing a cat but to swing the gun turret of a Chieftain tank!

Such screened rooms are designed to exclude any external RF signals so that measurements can be made without outside interference.  Even under-floor screening is necessary. Older rooms were made from two wire mesh cages one inside the other, while later models are solid metal boxes.  All power and telephone lines have to be heavily filtered to prevent any signals from by-passing the screening.  Doors close tightly and have “spring fingers” to prevent any “slot aerial” effects.

To get back to the locked room, we were asked to test a mobile screened room for use by REME units working away from their base workshops.  It was a solid metal job on the back of a truck, with just one door.

The usual procedure was followed, with measuring receivers and aerials inside the room and a series of transmitters and aerials outside.  Signal level  was measured with the door open and again with it closed, the difference giving a measure of the attenuation. As was usual with a solid room, there was barely any discernible signal with the door closed, but somewhere in the region of 700 MHz there was a sudden peak in signal level.

Most of the team were vehicle electricians who had learned enough radio to conduct specified tests, so as far as they were concerned this was a puzzle worthy of  Sherlock Holmes or Miss Marple!

After a certain amount of  brain-racking, I realised that the metal door-handles were about a quarter wavelength long at the offending frequency. So, the outside handle received the transmitted signal which was then conducted  through the lock to the inside handle which promptly re-radiated it to the receiver.

I can’t remember whether there was electrical continuity between the lock spindle and the door itself but I assume there was not.

I never heard the end of the story because the room was returned to the makers and it had not re-appeared by the time I left the establishment.

Funny stuff RF!

Return to the index of Vital Spark articles.

Jakey – (G3JKY). From VS April 2009.

G3MGQ’s Month on the Air

Prepared by the clubs RSGB trainer, G3MGQ, you will find the latest DX contests including the ones to shoot for as well as ones to give a wide berth. Why not download the latest edition of Month on the Air and enjoy your DX just that little bit more.

Become a member of HERC

Join the Hastings Electronics and Radio Club.

Why not join one of the largest and most established Radio clubs in the South East of England? Very low joining cost, and free for a year to new licencees.

Vital Spark Archive

Vital Spark newsletter articles

Take a look through a large selection of articles written by club members over the years which have been published in the monthly Vital Spark newsletter .

Used Ham Radio Equipment

View HERC's Used Ham Radio Equipment for sale list..

Every four weeks, HERC's Used Ham Radio Equipment for sale list is updated on the site. Bookmark the gear for sale page to re-visit easily and take advantage of the used equipment on sale through the club.

Club Photographs

HERC Image Galleries.

Here is the official HERC photograph archive which contains multiple image galleries spanning several decades since the club was formed many years ago. Enjoy the images!

UK Amateur Radio Repeaters

UK repeaters

Click button above for full list, or a local repeater callsign below for info.

GB3EB 2m in Uckfield- Active
MB6EB 2m DStar Node in Eastbourne - Active
MB6RY Wires-X DigiGate in Broad Oak - Active
GB3HE 70cm in Hastings - Active
GB7HE 70cm DStar in Hastings - Coming soon
GB3ZX 70cm in Eastbourne - Low Power
GB3JT 23cm ATV in Hastings - NoV cleared
GB7RY 70cm X-Wires Repeater Rye - Active
GB7ES Eastbourne - DSTAR Rpt. - Active
GB3ES 2m in Hastings - Active

For a complete list of repeaters, head over to
the UK Amateur Radio repeaters list.

Popular pages

Get your amateur radio licence - Find out more about amateur radio licence training.
Month on the Air - G3MGQ's popular monthly DX contest/expedition list.
Wilf Gaye Memorial Cup - The clubs annual operating event in the memory of Wilf Gaye M0GYE.
St. Richard's College Buildathon/STEM/ARISS - HERC attends St. Richard's Catholic College for their various events surrounding the Tim Peake ARISS contact.
G3BDQ - John Hey's Rare QSL Cards.
Sussex Electronics Radio Fair - SERF Sussex Electronics Radio Fair 2016.
Vital Spark - A selection of articles re-published from the Vital Spark.
RSGB News - Find out how to get RSGB news on your mobile or PC.
Experimenters Corner - A selection of Proteus projects by Bob Gornal (G7DME)
BBADL - Bath Based Distance Learning Course.
Conquest Hospital Radio - Presented by HERC member Antony (G4CUS).
Radio Rallies 2016 - An up to date list of radio rallies scheduled for 2016.
Club QSL Cards - A selection of QSL cards the club has received over the years.
Other Newsletters - Excellent newsletters and magazines from other clubs.
TX Factor episodes - Take a look at the TX Factors YouTube videos.
John Taplin - A bio of the late John Taplin.

Amateur Radio Resources

Other Radio Clubs & RAYNET

BSARS - Brede Steam Amateur Radio Society

RAYNET - The Hastings and Rother RAYNET Group.

HERC members sites

Sigord - Gordon Sweet
Hastings Radio Comms - Andrew Haas-Campbell
Hoofbags - Liz Costa

Categories