MARSRADIO
Phone Patch Net
Phone Patch Procedure And SELCAL
The USAF MARS Phone Patch Net provides worldwide 24 / 7 / 365* telephone service to US military aircraft via HF radio.

All US Air Force, Army, Navy, Marines and Coast Guard Aircraft are supported. The net is staffed by Amateur Radio (Ham) volunteers who are members of MARS (Military Auxiliary Radio System). US Air Force MARS is sponsored by the Air Force 38th Cyberspace Readiness Squadron  (AFSPC) at Scott AFB, Illinois.  There is no charge for using the Phone Patch Net.  Only DOD aircraft or units are authorized to use the net.

Contacting A MARS Station

There are several things to keep in mind when calling MARS Radio:

Use the primary frequency first and call MARSRADIO. All MARS stations monitor the primary frequency both day and night. The alternate frequency if there is no answer on the primary. 

Often times the MARS station can improve reception if the operator knows which way to aim the antenna. At times, having the antenna pointed correctly can make the difference between Loud and Clear and Weak, Barely Readable.

Call multiple times. To avoid confusion, the only station that will answer you on the first call is the Net Control station. If Net Control does not hear you, other stations will respond after your second radio call. This is why you should always call several times. Also, if you are answered by an operator other than the net control, he will usually first contact the NCS to see who will handle your patch.

                               EXAMPLE RADIO CALL:    MARSRADIO, REACH 123, NORTH ATLANTIC, OVER

If after calling several times you do not get any response try the alternate frequency.  Try again in 20 - 30 minutes when propagation may be different due to the time of day, and/or your location if still unable to raise an operator.

Another station may be asked to run the patch. Operators are volunteer and every attempt is made to spread out the phone patches so all stations can be involved.

Running A Phone Patch

Once initial contact has been established, the MARS station will ask you for your phone patch request. Give the operator the phone number to be dialed, and if making a morale call, YOUR first name. The net normally does not need the name of the party being called unless you feel that is important.  Keep in mind that the phone call is NOT secure, as it does go out over short-wave radio. This is the reason that last names are not normally used.

Morale calls are made courtesy of the individual operator who normally has unlimited dialing within the US. Some stations can do international calls. Official calls can be made to a DSN or commercial number.

Your phone call may be picked up by an answering machine. Normally, the MARS operator will give you the option of leaving a message on the machine. If you know that you do not wish to leave a message, you should advise the operator of this when placing the call.

Since this is a radio phone call, each party must take turns talking. You cannot both talk and listen at the same time, as you do over a regular telephone. It is proper procedure for both parties to say the word OVER at the end of each transmission so that the MARS operator knows when to key the transmitter.

Morale calls should be limited to 5 minutes. Official calls do not have a time limit, and have at times been known to run several hours.

When you are finished with your patch, you should advise the MARS operator to TERMINATE THE PHONE PATCH so that the end point of the patch is clear to the operator.

Advise the operator if you have another request. As MARS operators take turns running patches, you may be routed to a second operator. If the reception of the second operator is not satisfactory, you may request net control to assign you a different operator. The Phone Patch Net wants to provide the highest quality patch possible.

 * Based on volunteer availability and propagation

Selective Calling (SELCAL)

The phone patch net has limited capability of broadcasting a SELCAL.
 
Currently there is one station located in Arkansas.  Propagation might be different to the aircraft from the SELCAL broadcast location than the controlling net station.  HF SELCAL is used by ATC for international flights however it is available for any flight on the MARSRADIO primary frequency.  An aircraft must be tuned to the MARSRADIO's primary frequency to receive the alert.
​​"SELCAL operates on the high frequency (HF) or very high frequency (VHF) radio frequency bands used for aircraft communications. HF radio often has extremely high levels of background noise and can be difficult or distracting to listen to for long periods of time. As a result, it is common practice for crews to keep the radio volume low unless the radio is immediately needed. A SELCAL notification activates a signal to the crew that they are about to receive a voice transmission, so that the crew has time to raise the volume.  

An individual aircraft has its own assigned SELCAL code. To initiate a SELCAL transmission, a ground station radio operator enters an aircraft's SELCAL code into a SELCAL encoder. The encoder converts the four-letter code into four designated audio tones. The radio operator's transmitter then broadcasts the audio tones on the aircraft's company radio frequency channel in sequence: the first pair of tones are transmitted simultaneously, lasting about one second; a silence of about 0.2 seconds; followed by the second pair of tones, lasting about one second.

The code is received by any aircraft receiver monitoring the radio frequency on which the SELCAL code is broadcast. A SELCAL decoder is connected to each aircraft's radio receiver. When a SELCAL decoder on an aircraft receives a signal containing its own assigned SELCAL code, it alerts the aircraft's crew by sounding a chime, activating a light, or both.

The crew next turns up the volume on the aircraft radio to hear the incoming voice transmission. Using ICAO radio protocol, they must verify with the transmitting operator that they are the intended message recipients. The crew then uses the received information."    (https://en.wikipedia.org/wiki/SELCAL )

An aircraft may request that they be notified via SELCAL on the MARSRADIO primary frequency if they do not want to listen to the background static.  Aircrew should contact MARSRADIO within an agreed time period if no SELCAL has been received in case propagation has changed from the broadcast site to the aircraft.

Base operations may request a SELCAL attempt with an aircraft via the net's PBX system.  The aircraft will need to have their radio tuned to the MARSRADIO primary frequency and be within range of the broadcast site.

Further information may be obtained by emailing us through the contact page .