HISTORY:
These curious devices date back the 1970's when remote control of devices and equipment was commonly performed by sending audio frequency tones (sub-tones and dual tones), often via a radio communications link. The audio frequency accuracy and stability was critical to these applications, these devices were manufactured to an accuracy of 0.5Hz
These devices were used for everything from remote controlled garage doors, pagers, security access systems etc
While there may not be a call for such devices with modern digital based equipment, these could well provide an extremely accurate source for custom designed audio frequency reference oscillators OR special audio frequency filter systems.
Used in VERY OLD audio tone based remote control equipment...well before the days of PLL's such as the NE567 - no digital here, everything was analog based
Used for both tone generation or as part of an audio tone filter
MURATA (Japan) - Tuning Fork Resonators (also referred to as "Microforks")
Made in Japan
USED Ex radio communications equipment "PULLS" absolutely functioning, these were removed from working (but of course obsoleted) equipment
Various frequencies (see the selection list)
I have more of these (different frequencies) from another Japanese manufacturer, take a look HERE
Never seen one of these? They were used to filter or generate audio signals, I also have the "associated devices" such as the Murata D1200 and D1055 to make a complete analog tone control system.
These microforks were considered "hi tech" in their day as prior to these special devices, discrete LC tuned circuits were used for these audio frequency functions.
They have three terminals, input, common and output, physically very small - they appear very similar to crystal filters but these microforks are ONLY for much lower audio frequencies than quartz crystal based systems and use a piezo element.
So specialised and precision was the manufacture of these means that some of these devices (the larger case type) has its own manufacturing serial number - almost hand made!
Bandwidth is 2 ~ 5 Hz
They are used as band-pass filter or resonator in high stability audio oscillators
The frequencies I have available are in the list provided in this advertisement, just select which frequency you require and the correct resonator will be sent to you.
There is two types (sizes) of packaging:
All are identified by MuRata as Type EFM
The larger packaging is type EFM-S and the smaller, EFM-G
EFM-S
All metal case body except the underside which looks to be a resin
Measures 32mm x 7.8mm x 7.85mm height
All of the resonators have this package type EXCEPT the 879.0Hz frequency
EFM-G
All metal case body except the underside which looks to be a resin
Measures 18.15mm x 7.25mm x 8.5mm height
Very interesting devices to experiment with - I can supply a very detail 22 page applications book (pdf format) - one of the photographs shows a very simple and yet extremely accurate audio oscillator built around these devices.
Each resonator is individually packed into a sealed, clear plastic packet
2500.0Hz
1700.0Hz
967,5Hz
879.0Hz (2)
877.5Hz
832.5Hz
802.5Hz
Very interesting devices to experiment with - I can supply a very detail 22 page applications book (pdf format) - one of the photographs shows a very simple and yet extremely accurate audio oscillator built around these devices.
