Transceiver, RT-1446/URC - Harris RF-350K:

NSN: 5820011623402

The RT-1446 is a microprocessor-controlled transceiver, conservatively rated at 100W Peak Envelope Power (PEP) and Average (AVG). The solid-state power amplifier ensures continuous rated output power during key-down operation. All operating and metering functions of the transceiver are fully remote controllable over 2/4-wire telephone lines.

Additionally, the built-in telephone patch and internally mounted AFSK option provide full communication flexibility.

Nomenclature

RF-350 is a 12 Volt radio without the attached power supply on the bottom.

RF-350K is a radio with the RF-366 power supply attached.  It can work on AC or DC power.

A RT-1446/URC  is the military designator for the RF-350K. 

A AN/URC-119 is a RF-350K system with either a 500 Watt or 1000 Watt LPA and automatic coupler.  

A AN/URC-121(V)  is nomenclature for a "portable" RF-350 based system.   The system is housed in 19 inch rack transit cases.  The 500 Watt LPA or RF-7210 Adaptive controller may be included.  

TECHNICAL

Block diagram of the transceiver in .pdf

Modification to use internal wiring for external speaker from terminal block on back of transceiver.

Modification to use 400 Hz CW filter in RTTY and other narrow digital modes.

Phone Patch hookup

IF frequency scheme

Modification pages have large graphics and will take time to download.  This is so you can print the diagrams on a full sheet.

 

TRANSMIT PATH

In the transmit mode, the 100W transceiver accepts audio/key-line inputs from a CW key, handset/mic, telephone line, or other source, and impresses the audio on a 455kHz intermediate frequency (IF) carrier. The 455kHz IF is raised in two conversions to the 1.6 to 30MHz transmitting range and amplified to a signal level of 100W PEP or AVG into a 50-ohm load.

A directional bridge in the transmit path measures the forward and reflected power levels. This information is used for front panel display and for transmitter gain control functions. A transmit/receive (T/R) switch separates the transmit and receive paths, which allows connection to a common antenna.

RECEIVE PATH

In the receive mode, the 1.6 to 30MHz received signals bypass the power amplifier and are reduced to a 455kHz IF using a double conversion process. The first conversion is made at an IF of 40.455MHz and band pass filtered to remove undesired image frequencies. The second conversion is made at an IF of 455kHz and band pass filtered to achieve selectivity. The resulting 455kHz IF signal is demodulated with an amplitude detector (Amplitude Modulation (AM) Mode) or product detector (Single Sideband (SSB) Modes) to obtain the audio output.

Control of the 100W transceiver is from the front panel or by remote input. Logic signals are processed by a microprocessor that provides the necessary memory, control, logic, and timing to coordinate the functions of the 100W transceiver in all modes of operation. The microprocessor also controls the detection and display indications of the Built-In Test (BIT) circuits. The synthesizer and reference/Beat Frequency Oscillator (BFO) modules generate the frequencies used in the modulation, demodulation, and double conversion processes. All reference frequencies are derived from a stable 10MHz frequency standard.

Click here for operating instructions for the RT-1446

NOTES AND INFORMATION:

I'm using a H161A/U headset, H-350 handset or M80 microphone with this radio and am receiving fine audio reports.  The H-350 is the telephone style handset typical on military gear.  You may also the H-250 as it is the essentially the same handset although the 350 seems to have a little bit more range in the microphone.  The M80 is a military hand microphone and I am told it sounds better than both handsets.  The H161U is a headset with a boom microphone, the headphones are great, but the microphone is like a Heil "DX Element".  All these microphones are noise canceling and have dynamic elements.  They are all for "communications quality" audio and you will win no awards from the hi-fi ssb crowd.  They usually can be found for under $20.  Check Fair Radio Sales or American Milspec.

Microprocessor in the radio is a 8088!

Interconnections - pin outs for various connectors including the power connector

Pin Out for Audio 2 connector.  Also sometimes labeled NBSV, this input is handy because you can switch audio and key-line in and out from the front panel by selecting AUDIO 2 with the AUDIO SOURCE button.  Originally for a KY-65 crypto voice unit, this is a good place hook up a PSK31 interface.  This corresponds to the DB9 on the back panel labeled AUDIO 2.  Both the transmit and receiver lines are balanced and isolated through 600 Ohm transformers internal to the RF-350.  Make sure the impedances are correct on your interface device, or you will see imbalance across the pass band with a range of frequencies being requiring less drive than others.  Response should be flat.  Pot. R29 on the Exciter Board will adjust the gain of this input should you need more drive.   

Fault Codes.

Manuals:

There are a few choices in manuals available.  Harris still supports the RF-350 radios and has manuals available.  It is a big book with lots of fold out drawings, but will tell you everything you ever wanted to know about the radio.  Expect to pay lots.  Since the equipment was military used, there are military manuals.  Typically Air Force TO are harder to come by than Army manuals.  The Air Force, to their credit, is a little more careful who they disseminate information to.  What you need to know about the military manuals is there are several different types and they are written for different audiences.  If you want a users book they have one.  If you want a board level repair book they have one of those too.  If you want a component level repair book it is called the depot manual.  The depot manual is as thick as the Harris publication and has all the schematics and fold out drawings. If you are repairing a broken radio, and you will be doing board level repair the depot manual is the book you want.

Some people on ebay and other places are selling manuals without fold out drawings.  Read this to mean no schematics.  The real money in the manuals is reproducing the fold out drawings..  

 Scott Sidener at www.american-milspec.com has the manuals on .pdf at very reasonable prices.  I say reasonable because, Harris wants hundreds of dollars for them, it cost more than a hundred dollars to make a paper copy of an original IF you can find one to copy.  They are generally not available on the used book / manual market.  Scott's are on .pdf so you only pay to print out what you need to have a paper copy of.  His manuals are complete and have the fold out drawings.  Scott has both the depot manual and Harris RF350K manual.  The fold outs are reproduced a little better in the Harris RF350K .pdf file than the depot .pdf, however, in both they are reduced to fit on one page (at least they print that way for me).

 

Sources for Equipment

There are basically three types of used RT-1446 radios out there.  

There are those sold as working and with support of the guy who sold them to you.  Toronto Surplus and Scientific is an example of a place that will sell you a radio in a known condition and stand behind it.  Their price is $2500 for the RT-1446 on their web page.

There are those radios sold "as surplused", unknown condition.  This CAN be a good deal.  What your looking for here is a radio that came from the DMRO with out anybody monkeying with it on the outside.  You will want a good description, etc., like if it was run over with a tank or de-milled.  I got two AM-7223 amps, CU-2310 couplers and 1 RT-1446 this way.  I got lucky and they all worked without repair.  If a repair is required, it is likely to be a single problem which is relatively easy to track down as the flow charts in the depot books assume a single problem.   I do know of people who purchased from the same source at a much later time and got radios in the following category:

Then there are those radios that are sold as surplus but they are not "as surplused".  What happened is the guy who was previously selling "as surplus" radios discovered he could get double (usually around $900) for a radio he could show worked, without providing any other support.  So when he ran into a radio that didn't work, he swapped parts with some of his other non-working radios.  He did this until he ran out of working radios, repairable radios and had only radios that he knew were full of faulty parts.   He would sell these radios, known to him to be faulty, as.... you guessed it, "as surplused".  The two cases I know of where this happened the modules inside the radio were not completely screwed in, rubber grommets not in place, and connectors loose or not seated at all.  These radios have several problems on several boards.  

 

 

Frequency display and keypad.

Analog controls and display window.

You will notice my back lights are out.  The LCD displays should be backlight by green light panels.  The power supply for the panels is a small black epoxy sealed inverter located under and just to the left of the FREQ, CHAN and MODE buttons on the circuit board.  It's output is 120 volts at 400 Hz and is the reason for the high voltage sticker on the back of the board.

455Khz Crystal filters. The two large ones are 2.7 KHz SSB filters. The small one is 400 Hz CW filter.

The power supply.  Here 110 or 220 Volts are brought to 28 Volts (big transformer lower right).  The 28 volts is rectified (strip between the gold box and fan) and brought to 13 volts in a switching supply in the gold box.  There is a toggle switch in here to set 110 or 220 Volts.  Also jumpers to set DC input for 12 or 28 volts.

 

Band pass Filter board.  On some units the relays here seem to get stuck bringing an A5 fault code.  Sometimes this can be cured by tapping on the relays and exercising them until they work again.

 

Transceiver circuits.  Receiver Board, Exciter Board.

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