Custom Products from Masters Communications

Brief Description:
Nothing beats having a real communications Service Monitor to test FM radios and repeaters for various functions, but they are incredibly expensive new, and even used ones (that are worth while) are commonly $2000.00 or more. There are inexpensive frequency modulated RF signal generators currently available that provide reasonable accuracy for testing receivers. These signal generators allow you to do basic sensitivity and simple audio tests including CTCSS tones. But, there are no manufacturers left making inexpensive test equipment for measuring FM deviation of transmitters. The Heathkit IM-4180, AEA DM-1, and MFJ-224 are long gone. I've owned all of these, and they are mediocre at best - even when they were brand new. The test equipment offered here is an attempt to provide a better solution than anything prior, with reasonable accuracy, on a hobbyists limited budget.

The FMDM-150M FM Deviation Meter provides direct / accurate measurement of Frequency Modulation from 0 to over 5kHz deviation with modulating frequencies from 50 Hz to over 4 kHz without the need of a computer, SDR, or spectrum analyzer or involving Bessel nulls or any complicated math. The system is comprised of several individual components that are available separately in kit form or assembled and tested and calibrated. The receiver is a current production Uniden "Bearcat" BC355N "police"scanner (chassis 367E) that is modified by adding a 3.5mm (1/8") stereo jack to its rear panel to bring out discriminator audio and a squelch logic signal. These signals are routed through a stereo audio cable (included) to the Analog Measurement Unit where the discriminator audio is processed, and made available to the different meter displays. The "AMU" is the heart of the system and is powered by a source of 12VDC (power supply or battery - not included). A small AC power supply is available separately.

There are two outputs on the Analog Measurement Unit - one drives the Analog (needle) Meter Display (AMD) and the other drives a (LED bar-graph) Digital Meter Display (DMD). A short connecting cable is included in the purchase of each display type. The analog meter displays deviation in kHz and frequency error in kHz. This meter "panel" also has a female BNC jack to connect an oscilloscope (not included) for waveform analysis / seeing distortion. Connection to an oscilloscope normally requires a BNC-M to BNC-M cable (not included - but available separately). Both types of meter displays are very accurate and capable of displaying the amount of FM deviation in the form of analog voice, digital voice or data, CTCSS / CDCSS tones, DTMF tones, VARA FM [QAM] (wide or narrow) and 1200 / 9600 baud packet - to name a few.

What's Required:
The Uniden BC335N scanner is a programmable / frequency agile receiver covering several commercial and amateur HF / VHF / UHF bands. Deviation and Frequency Error (offset) measurements are built off of this receiver platform, and it is a required component. The scanner is available already modified for directly connecting the Analog Measurement Unit. All of the components of the deviation measurement system are available separately, but, a modified scanner, analog measurement unit, and one display type is required to make deviation measurements. Optionally, you can purchase both display types if you like. Except for the scanner, everything is available in kit form or assembled/tested and calibrated. There are no cables to build - the components connect together with pre-made cables that are included with the purchase of the corresponding component. Powering is available for those that don't already have a suitable 12VDC power source. Powering pigtails are included with the purchase of the scanner and analog measurement unit. Power for the digital meter display comes from the analog measurement unit, and doesn't require a separate power source.

Simple Operation:
To measure deviation, connect the assembled / calibrated modules together with the supplied cables, apply power to the scanner and AMU, set the frequency into the scanner, and read the deviation on the meter(s).
Optionally, store the frequency into one of the 300 memory channels to be later recalled (or scanned).

Please navigate to and read the detailed description page below - when you have time.
Detailed Description of the FMDM-150M FM Deviation Measurement System.

Features:

	Small size - - does not require a computer or expensive / difficult software.
	Simple to hook up and use. Takes the guess work out of setting transmit audio levels.
	Measures and displays deviation directly - in both analog (needle) and digital (LED bar-graph) formats.
	Frequency Coverage of the BC355N Scanner: VHF Low Band = 25.0000 - 54.0000 MHz 28 - 54 MHz FM Aircraft Band = 108.0000 - 136.9916 MHz (AM) VHF High Band = 137.0000 - 174.0000 MHz UHF Band = 406.0000 - 512.0000 MHz 800 MHz Band = 806.0000 - 823.9875 | 849.0125 - 868.9875 900 MHz Band = 894.0125 - 956.0000 MHz
	Accurately measures all Two-Way FM modulation forms from 0 to over 5 kHz deviation from DC to 3kHz of modulating frequency within 4% accuracy. The frequency response extends from 30Hz to beyond 5400Hz at 10% or better accuracy.
	Deviation is read directly on the left analog (needle) meter and accurate within 4% for modulating frequencies of 3kHz and under - immediately upon power up. The digital LED display is considerably more graular but still very effective for most applications. The oscilloscope output is accurate within 2% deviation across its frequency range.
	Frequncy Error is shown on the right analog meter and is accurate within 200 Hz or better after a 10 minute warm-up of scanner. This is a center zero analog (needle) meter reads +/- 5kHz carrier frequency.
	Oscilloscope output (located on AMD) is calibrated for 100mV P-P / kHz of deviation. Very flat frequency response from DC to more than 5kHz.
	Power Source for Analog Measurement Unit (AMU) +12VDC nominal - regulated - 1A (not supplied - available separately).
	The AMU has onboard voltage regulation for all critical signal processing, measurement, and logic circuitry.
	Can be operated for several hours from a small 12V storage battery (not included).
	An affordable alternative to a service monitor - providing very reasonable accuracy. Assembled-Tested-Calibrated units are calibrated using equipment with NIST Tracable Calibration.
	Cables to connect the components together are included in the purchase. BNC-M to BNC-M cable available for an added fee.
	DC Power Cables (pigtails) are supplied with the Uniden Scanner. (When purchased already modified from us) and also the Analog Measurement Unit (AMU).
	The analog meter display 'panel' (AMD) does not require a power source. The digital (LED) bar-graph display (DMD) gets its power from the AMU.
	A perfect companion to the popular FM RF signal generators (marketed as walkie-talkie testers) available on eBay and other outlets. Gives you the capability of many of the tests provided by a real Service Monitor at a fraction of the cost.
	90 day Limited Warranty.  Repair and Recalibration available for units out of, or not covered under warranty (my determination).
	Calibration of the units should last for years of normal storage and service. TBD.

 

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