UHF - Ultra High Frequency

Frequency Range   225-399.975 MHz
Power Out            10 watts

A quick look at Havequick

Jamming an RF radio can take quite a bit of power, which means that one generally sticks to one frequency as it would take a lot of power to jam multiple frequencies. So, to foil jamming, the ARC-164 uses Havequick, which employs frequency hopping. By quickly jumping to various channels, the radio can evade attempts at jamming by minimizing exposure to any one frequency.

To accomplish frequency hopping, both users must have a pre-established channel-hopping pattern as well as a number of preselected frequencies, of course, they need to synchronize their systems so that they are also on the right channel at the right time. The WOD or Word-of-the-Day determines the pattern, rate, and dwell time, and can either be transferred via a cryptographic loading device or manually input. To synchronize internal clocks, you need a valid TOD or Time-of-Day. You can receive TOD from a ground station, aerospace vehicle or even another system like GPS. TOD from one of these sources will allow you to use havequick and communicate with any other aircraft worldwide. However, if you do not have a universal TOD available, or do not wish friendly aircraft to listen, you can randomly generate your own TOD, which will be out of sync with other aircraft. Then you can pass your random TOD to aircraft of your choice for communication with only those aircraft which you have passed your unique TOD to. Finally, you need to choose a net number which is the actual table of frequencies you will be using. This is selected with the frequency select knobs on the UHF control.

Using the radio buttons below the text box and on the right, you can see how the 3 elements are used to make Havequick happen:

Radio #1                 Radio #2
Radios on
Radios off
#2 WOD match
#2 WOD unmatch
#2 TOD sync
#2 TOD desync
#2 Net number match
#2 Net number unmatch
EDIT (2010): Argh... it looks like I was taught incorrectly. Here's an excerpt from JP 6-06.1 that properly explains net number:

c. Net Number Assignment. The net number, a three-digit number, enables several radios using the same WOD and TOD to communicate without interfering with one another. The net number determines the frequency in the hopping pattern at which the radios in that net begin to hop. Because there may be many more nets required for an operation than there are net numbers available, HAVE QUICK planners must assign net numbers carefully. This minimizes the number of users with the same net number in the same geographical area and thereby reduces the opportunity for them to interfere with each other.

ARC-164 LRUs

ARC-164 R/T RT-1504 - The only really notable points of interest about the R/T are that it has two receivers (one main, one guard) and the ECCM slice (Electronic Counter Counter Measures). Other than that, there isn't too much to point out. Remember that when you remove or reinstall a remote R/T, you need to be careful of the single wire that is hooked up in the back. If you forget, you may break the wire off.
C-11719 - It's important to understand the control functions. The main function switch has four positions: Off, Main, Both, ADF. In Both, both the Main Receiver and the Guard receiver are activated so that the radio operator can communicate as normal with the main reciever and transmitter while listening to the guard channel for emergency response. If the aircraft is equipped with a UHF direction finding system, the ADF position will activate the UHF/DF antenna and actuate relays so that the system uses a DF antenna instead of the comm antenna. The DF antenna independantly drives toward the station and sends bearing signals to the appropriate instrumentation. Meanwhile, the RF signal is still sent to the UHF R/T for demodulation of the audio.

The M-P-G switch has 3 positions: Manual, Preset and Guard (GRD). By selecting manual, your opertaing frequency will reflect what you have dialed in. In preset, you will use the selected preset. By putting the switch in Guard, you will be operating at 243 MHz. The operational difference between this and the Both function, is that in Both, you want to listen to the guard channel. But if you want to make an emergency transmission, you want GRD. Selecting GRD tunes the transmitter and main receiver to 243 MHz. If you leave it in Both, the guard receiver will be disabled so that you do not burn it up with your your guard transmission (just as the receiver is not receiving when you transmit for any radio).
ARC-164 Control

Then, there's the T-Tone switch. T is primarily for the receiving TOD. If you are tuned to a station that is transmitting TOD, actuating T will allow you to receive TOD for a short period of time. Conversely, Tone (in addition to creating a 1020 Hz tone) will allow you to transmit your TOD. And if you want to generate a random TOD, you simply hold Test Display and actuate T. You should hear a peculiar squelch break when you do this that sounds the same as when you receive TOD.

Basic Troubleshooting

The ARC-164 is a pretty simple system to troubleshoot and a very easy system to maintain if you're fortunate enough to have a panel mount installation. For the purposes of this training guide, we'll stick to remote (control and R/T are seperated), which is still easy to troubleshoot, but less easy to maintain if the R/T is in a difficult location.

As always, when dealing with any radio tied into a secure system, it's important to realize that the secure equipment can sometimes cause problems even when it's completely turned off. This means you could have a problematic KY-58 processor or if installed, Z-AHQ adaptor (which is used to retro-fit the KY-58 into KY-28 installations) or a guard relay.

Most problems, however, deal with the R/T and transmission elements (cabling or possibly an antenna). Anytime you have a transmission problem, you need to bring out a wattmeter and TDR. These 2 pieces of test equipment can help you to find the problem.

Take the UHF test
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