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===== Collins R-392 / URR =====
Manufactured by [[Collins|Collins Radio Comp., Cedar Rapids]].

The Collins R-392 is a double / triple conversion receiver technically based on the legendary R-390, the design of which was reduced to a mechanically very compact format; the receiver was mainly used onboarf vehicles. The receiver R-392 was developed by Collins and also built by several contractors under licence.

{{:images:collins-r392.jpg?direct&400|Collins R-392}}
==== Technical data =====
  * [[Principle]]: [[triple conversion superhet]], [[IF]] 9.5 - 18 MHz / 3 - 2 MHz / 455 kHz
  * [[Operating modes]]: [[A1]] with BFO, [[A3|AM (A3)]]
  * [[Frequency range]]: 500 kHz - 32 MHz
  * [[Frequency display]]: mechanical - digital display, 100 Hz
  * [[Frequency memory]]: none
  * [[Signal strength indicator]]: [[S-Meter]]
  * [[Signal processing]]: [[RF Gain]], [[AGC]], Antenna trimmer
  * [[Sensitivity]]: [[A3|AM (A3)]] / [[Selectivity]]: 2 / 4 / 8 kHz (-6 dB)

==== Power supply ====
  * [[Batteries|Accumulator / Battery operation]]: 28 V DC (on-board power supply)

==== Dimensions ====
  * 275 x 360 x 275 mm, weight 23.7 kg

==== Accessories ====

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{{:images:collins-r392-front.jpg?direct&400|Collins R-392}}
==== Operation =====
The Collins R-392 was developed as a more compact variant of the Collins flagship receiver [[R-390]] for use on military vehicles, with a minimal footprint.

The receiver comes in a 27.5 x 36.0 x 27.5 cm splash-proof aluminium die-cast cabinet that looks fairly cubic. All controls and connections, unfortunately many of them are military multipole connectors, are located on the front panel.

The receiver is operated with 28 V DC, the power consumption is a considerable 85 watts, so an external power supply is usually required.

The receiver covers the range from 500 kHz to 32 MHz in 1 MHz segments. The reception frequency can be read directly on a mechanical counter (mechanical digital display), the display of which is similar to an odometer. The MHz digits are set using the left-hand knob and the kilohertz digits from 000–999 are set using the right-hand tuning knob below the frequency display. With its 200 Hz dial lines, a maximum frequency accuracy of up to 100 Hz is possible. In the 0.5–8 MHz range, the receiver acts as a triple conversion superhet, and on higher frequencies as a double conversion superhet.

The R-392 has a BNC and a long-wire antenna connection. The antenna signal is fed to the first mixer via a mechanically controlled tracking preselector and two RF amplifier stages.

To achieve absolute frequency accuracy, calibration is necessary before operation. The CAL calibrator (same knob with the AGC switch) provides a calibration signal every 100 kHz. The counter is set exactly to a 100 kHz dial setting using the KHz button, then the counter is decoupled from the VFO by turning the Zero Adj. button clockwise. With a bandwidth of 2 kHz and the BFO switched on, the pitch control in the 0 position, the set is now tuned to zero beat, i.e. the kHz knob is turned until the whistle becomes lower and disappears; the drop in the line level meter to O can also be observed. Turning the Zero Adj. knob to the left causes the counter to reconnect to the VFO, and now the frequency display is set with a dial accuracy of 200 Hz.

{{ :video:collins-r-392-mixer-slug-table.mp4?&400|Mechanically synchronised preselector}}To receive a signal, turn the main switch to the NORMAL position, turn the RF Gain clockwise to the full stop (the line on the knob is difficult to see), set the AF Gain (volume) in around middle position, [[AGC]] on ON, [[BFO]] on OFF, bandwidth 4 KC. The frequency is now set using the MHz and kHz tuning knobs. The pre-selector is mechanically tuned using numerous synchronisation discs that are moved by gears; this mechanically implemented tracking preselection gives the receiver great performance with high rejection of image frequencies and immunity to large signal effects.

The desired frequency, for example 6,155 kHz, is now set reading the frequency from the mechanical counter, and a "dial lock" control allows the main tuning to be mechanically locked. With the bandwidth switch, you can select the appropriate filter for the reception situation: I usually use the 8 KC filter for uncomplicated AM reception. If one of the two 5 KHz adjacent channels is occupied, I recommend switching to the 4 KC filter. This and the 2 KC filter, although coil filters and not the famous Collins mechanical filters are used, provide the receiver with a very useful selectivity. A switchable BFO enables the reception of [[CW]] signals and, to a limited extent, SSB transmissions. If you try ECSS reception, the reception of only one sideband of an AM signal, the receiver is not an outstanding performer.

Finding a power supply for the receiver is demanding: A sufficiently powerful 28 V power supply is necessary (with less than 25 V, the performance of the receiver drops significantly). Equally difficult is the connection of headphones. As special military connectors are used, it is important to ensure that a corresponding plug or connection cable is included when buying a second hand set.

==== Technical principle =====
{{ :images:collins-r392-top.jpg?direct&300|Collins R-392 chassis from above}} In the frequency range from 0.5 to 8 MHz, in which the receiver acts as a triple conversion superhet, a first IF between 9.5 and 18 MHz is generated and then converted to the range 2 - 3 MHz in the second mixer. When receiving frequencies above 8 MHz, this step is bypassed and the signal is fed directly to the second mixer.

At the second mixer, a crystal signal selected with the MHz knob is added so that the mixing product always results in the 3 - 2 MHz range, thus generating the second intermediate frequency.
The kHz tuning within every 1 MHz range is derived from the signal of a high linearity permeability-tuned oscillator so the last intermediate frequency of 455 kHz is created. The permeability-tuned oscillator is driven via numerous gears, which also drive the mechanical counter.

This intermediate frequency is routed through the three coil IF filters 2 / 4 / 8 kHz. Similar to the original R-390 (not the a version), the legendary Collins mechanical filters are not used in the R-392.

After the IF amplifier stages, the signal is fed to a diode demodulator for AM reception. The BFO oscillates on a variable frequency between 452 and 458 kHz, so the BFO control range is +/- 3 kHz. This makes SSB reception possible; in difficult situations, the RF gain must be carefully adjusted manually. Next follows a noise limiter stage and a squelch circuit, above a certain RF level, the NF is switched on by a relay to the outputs. The AF output signal of 200 mW at 600 ohms is suitable for operating headphones, a 600-ohm speaker (e.g. [[LS-166]], which comes with the matching plug) or for driving an AF amplifier; the R-392 does not have a built-in speaker.

===== Components ====
{{ :images:collins-r392-bottom.jpg?direct&300|Collins R-392 chassis from below}} The device is equipped with radio tubes. As a special feature, all the battery tubes operate with the operating voltage as a very low plate voltage of 28 V. For this reason, reception is particularly susceptible to a drop in battery voltage. If the receiver is supplied with 24 V, the receiver sensitivity is fairly reduced.

Since the receiver is hermetically sealed in the closed cabinet, the interior is usually in good condition. After loosening the ten captive screws, the receiver can be pulled out from the front of the cabinet. When turning the tuning and changing the bandranges, the action of the tracking preselector, which is driven by gears, can be observed.

==== Technical documents =====

==== Development ====
{{gallery>:images?collins-r392*.jpg&0&80x80&lightbox&showtitle&titlesort}}

==== Further information ====
* [[https://www.radiomuseum.org/r/collins_r_392urr.html|Collins R-392/URR on the www.radiomuseum.org website]]