View source for AN/URM-25D Signal Generator

{{Infobox laboratory equipment
|name     = 
|image    = URM25d-SignalGenerator.jpg
|alt     = 
|caption   = URM-25 Signal Generator c. 1955
|acronym   = 
|other_names = 
|uses     = Aligning antique radio equipment
|notable_experiments =
|inventor   = 
|manufacturer = Various, commissioned by U.S. Military 
|model    = 25D
|related   = 
}}

The '''AN/URM-25 Signal Generator''' was a device used during the 1950s and 1960s by the [[U.S. Military]] to test [[electronics|electronic]] equipment.

==History==
The AN/URM-25 were part of a series of [[vacuum tube]]-based [[signal generators]] built for the U.S. Military during the [[Cold War]]-era. 

Today they are collected and used by [[vintage amateur radio]] and [[antique radio]] enthusiasts who say they provide a reasonably high accuracy and stability for a low cost with build quality reflecting tough military construction standards.<ref name="r-390a.net">http://www.r-390a.net/Pearls/URM-25.pdf ''R-390a.net'', URM-25x discussions</ref>

==Specifications==
[[Image:URM25D-SignalGenerator-FreqMeter.jpg|thumb|150px|right|w/Freq. Meter]]

RF ([[Radio Frequency]]) can be varied between 10&nbsp;kHz and 50&nbsp;MHz with [[modulation]] selectable at 400 and 1,000&nbsp;Hz. RF level from .1 to 100,000 microvolts or 2 volts is available depending upon termination load. [[Output impedance]] is 50,500 ohms. 

Carrier oscillation is performed by 6AH6 with an additional 6AH6 buffer stage followed by a 6AG7 output amplifier. Modulation oscillations at 400 and 1,000&nbsp;Hz are provided by [[5814A]]. URM-25x models also contain internal VTVM ([[Voltmeter#Vacuum_Tube_Voltmeter_.28VTVM.29|vacuum tube voltmeter]]) and crystal calibration.

The carrier frequency can be set by interpolation using the graduated dial. Additionally, the URM-25's have a [[BNC connector|BNC jack]] for constant 200 mV output that can be connected to a frequency meter to eliminate guesswork. A sufficient warm-up period is required to ensure the best stability at higher frequencies.

The cabinet cover includes accessories such as an impedance adapter, fixed attenuator and antenna simulator. Additional accessory kit MK-288 includes adapters and more dummy loads.<ref>''R.F. Signal Generator Set AN/URM-25D'', by United States Dept. of the Army, Dept. of the Army, United States Air Force, United States, Air Force. Published by Departments of the Army and Air Force, 1993</ref><ref>''TM 11-6625-278-20P, DEPARTMENT OF THE ARMY TECHNICAL MANUAL'' ORGANIZATIONAL MAINTENANCE REPAIR PARTS AND SPECIAL TOOL LISTS, SIGNAL GENERATOR SET AN/URM-25D</ref>

==Nomenclature and Model Differences==
The URM-25 units were released in several series from 25A through 25J and some can have substantial differences in both circuitry and configuration from previous models. It is common to find units having differing identification tags; i.e. front face tag may differ from the cabinet tag. Additionally, some units have additional minor circuitry that do not show up on the schematic. The "URM" code is broken down to indicate General Utility, Radio, and Maintenance and Test Assembly.

==Overhauling==
Some present day electronic hobbyists say the URM-25 series is a good cost-effective choice to use for tuning radio equipment but overhauling can be tricky and time-consuming. Many say that the model F is easier to work on than the model D which is in relatively plentiful supply.<ref name="r-390a.net"/>

==See also==
* [[List of military electronics of the United States]]

==References==
<references/>

==External links==
*BAMA: Boat Anchor Manual Archive - http://bama.sbc.edu
*Example Overhaul: http://www.chuckg.com/urm25d_repairs.htm
*Example Overhaul: http://www.willydog5.com/index.php?option=com_content&task=view&id=27&Itemid=39
*Example Overhaul-capacitors, resistor replacement: http://www.wikihow.com/Restore-an-Urm-25D-Signal-Generator

[[Category:Laboratory equipment]]
[[Category:Electronic test equipment]]
[[Category:Military electronics of the United States]]
[[Category:Joint Electronics Type Designation System]]
[[Category:2Fix]]