Mystery RF(?) Items!  - Page 1
Forum section: electronics / rf-microwave

author: WikusVanDeMerwe
author_rank: Newbie
timestamp: January 18, 2024, 09:47:39 pm
content: Greetings All!I've worked for the government for most of career and along the way I've made it my business to be the go-to man for any old odd looking electronics I can sniff at in my lab during downtime...Recently a colleague who'd been in a sub sub basement somewhere had found some items they thought I would appreciate and of course they were correct.When I first got them I realised quickly they were too filthy to do anything with in the immediacy so I brought them home and I've spent the last several hours trying to remove the residue of the black foam that these things were fitted into inside their (very sleek I thought) looking containers. Real wood!I have done my best to try and figure out what these items are but I am totally stumped. The front face shown in the pictures below has a mesh screen behind the apertures, I'm not sure if this shows well in the pictures but it was hard to photograph as my fingers were and still somewhat are, covered in schmoo.Are these some kind of RF filter? A means of tuning a signal? Calibration?They're clearly not Microphones as the finder thought and have been etched with some information once you unscrew them at the end... Sadly I can find nothing on the company 'General Radio Company' it's a smidge non-specific for Google's taste and I'm not steeped in RF lore.Can anyone solve this mystery for me?Two stainless cylindrical devices of different lengths, both with fine pitch threads for screwing onto / into something, both with a face covered in circular apertures with a mesh screen placed behind. They were found in an old building that at one point had been used to monitor fallout - possibly unrelated.Many thanks all!

author: The Soulman
author_rank: Super Contributor
timestamp: January 18, 2024, 10:08:25 pm
content: General Radio is/wass a well known test equipment now owned by iet labs who have all the old General Radio catalogs online.Your device must in there somewhere..https://www.ietlabs.com/genrad_history/historic_catalogsI'd say it's some form of sensor+ampifier.

author: TimFox
author_rank: Super Contributor
timestamp: January 18, 2024, 10:20:38 pm
content: The General Radio Company of Massachusetts (also known as GenRad) was a renowned manufacturer of test and measurement equipment from 1915 until late in the 20th century, when they switched to ATE as a focus.That range was acquired by Teradyne, while their T&M went to IET, and GenRad ceased in 2001.During their heyday, they made sound meters, vibration meters, and acoustic noise meters, along with RF and component measurement units.Those units look like microphone heads for their acoustic meters.I’m surprised you weren’t able to find General Radio Co. in Google; the first thing that came to my search was a short Wikipedia article.I was often able to locate information and manuals for G-R equipment through Google.

author: Andy Watson
author_rank: Super Contributor
timestamp: January 18, 2024, 10:20:59 pm
content: I would say that they are microphone capsules - specifically for use with a sound level meter.https://ietlabs.com/pdf/Manuals/GR/genrad%20microphones.pdfSee page 13. Apparently the 1961-9611 is an electret microphone.Edit: Actually, it is page/section 1-1 as labelled in the above link, and has a picture fo the microphone capsule in its box.

author: berke
author_rank: Frequent Contributor
timestamp: January 18, 2024, 10:25:32 pm
content: Quote from: Andy Watson on January 18, 2024, 10:20:59 pmAlso see the 1973 catalog, p.87, 1961-9602 is a 5 Hz to 12 kHz electret mic.

author: WikusVanDeMerwe
author_rank: Newbie
timestamp: January 18, 2024, 10:32:26 pm
content: Thanks for the prompt reply gents, maybe it was my brain that was failing and not google, I am sorry google overlords for this affront to you!Fascinating, I had never heard of electret microphone thank you so much for the link to the old pdf Andy that will provide me with hours of entertainment!!

author: The Soulman
author_rank: Super Contributor
timestamp: January 18, 2024, 10:34:07 pm
content: Quote from: Andy Watson on January 18, 2024, 10:20:59 pmYep, found that one too, just love the read these old catalogs/manuals, so much better than the marketing crap we get these days.

author: WikusVanDeMerwe
author_rank: Newbie
timestamp: January 19, 2024, 04:18:41 pm
content: Hi Again all,I bought my friend a coffee and apologised for doubting his Microphone diagnosis although like me he'd never heard of this particular variety.Now... how to hook one up...

author: WikusVanDeMerwe
author_rank: Newbie
timestamp: January 21, 2024, 02:35:35 pm
content: Greetings all - a follow-up adventure and I scored the only other thing worth bringing back..It's another GenRad doodah!9V supply board seems in good condition, seems to have been inserted into some larger apparatus?

author: The Soulman
author_rank: Super Contributor
timestamp: January 21, 2024, 11:32:44 pm
content: Cool, it says on it what it does, puts out a 1KHz tone at an (accurate) 114 decibels.You put the microphone end of a sound level meter into the hole and see if the meter reeds 114 decibels, if not, adjust the meter.You have not yet found the sound level meter in the basement?

author: Gyro
author_rank: Super Contributor
timestamp: January 22, 2024, 10:30:49 am
content: 114dB at 1kHz is going to make you really popular with the neighbors!