Marine HF-SSB Simplex Frequencies

MF & HF-SSB Simplex Frequencies

So What is a Simplex Frequency?

The simplest definition is:

A frequency that you both transmit and receive on.

Simplex frequencies whether MF, HF, or VHF are primarily used for Distress, Urgency, Safety, Calling, and Ship to Ship communications. Rarely, they may be also used for ship to shore communications.

The International Telecommunication Union (ITU,) the same organization that sets international regulations and treaties governing Marine VHF usage is also responsible for the Marine Medium and High Frequency spectrum. The intent is to provide the maritime radio communications user with a group of standard distress, safety, hailing, and working frequencies that are known to all mariners and can be used worldwide.

So why is it that Duplex Frequencies can't be used for ship to ship communications? Well, technically they can. The problem is that it would require a completely different equipment setup than today's common VHF or MF/HF Transceiver found aboard most vessels.

So, Why Not Duplex?

Let’s Formulate an Example to Show You Why:

Say you are cruising along in Penobscot Bay, ME around 1300 EDT and you decide to call a friend on HF-SSB using DSC Routine Calling.

You know he is about 200 NM south of Bermuda, putting him somewhere in the vicinity of 950 NM away.

A quick check of the propagation tables tell you that for the time of day and the distance involved the 12 MHz Band is probably your best bet.

So you send out a DSC routine traffic alert on 12577.0 kHz with a suggested duplex working channel of 1201.

You receive an acknowledgement to your alert from your friend, then switch frequencies to channel 1201. Your friend also goes over to 1201 and waits for your voice call.

You then begin calling your friend on the radio and Lo and Behold: Nothing Happens!

So What Went Wrong?

The (2) vessels were trying to communicate on a common duplex frequency pair (channel). You can choose any ITU channel that you wish, but for this example we chose channel 1201.

ITU Channel 1201
Your Boat   The Other Boat
You Xmit You Recv   They Xmit They Recv
12,230.0 kHz kHz 13,077.0 kHz   12,230.0 kHz kHz 13,077.0 kHz

As you can see, both boats are transmitting on 12,230.0 kHz, and you are both listening on 13,077.0 kHz. Neither one of you are listening on 12,230.0 kHz the frequency everyone is transmitting on. Are we seeing the problem here? Neither party hears what the other is saying.

Public Coast Stations on the other hand are set up differently and that is why duplex channels work for them. When they dial up 1201 the frequencies are reversed. They are transmitting on 13,077.0 kHz and listening on 12230.0 kHz

ITU Channel 1201
Your Boat   Public Coast Station
You Xmit You Recv   They Xmit They Recv
12,230.0 kHz 13,077.0 kHz   13,077.0 kHz 12,230.0 kHz

This brings us back again to the use of simplex frequencies for ship to ship communications. Everyone transmits and receives on the same exact frequency, such as 12353.0 kHz. So everyone hears the traffic the other is sending.

Primary MF/HF-SSB Simplex Frequencies

Medium and High Frequency Simplex is provided for worldwide common use by ships of all categories and of all nations. By international agreement, it is used for communications with other ships or shore stations. Intership communications being the primary use for simplex frequencies.

Primary Intership Simplex Frequencies
2 MHz 4 MHz 6 MHz 8 MHz 12 MHz 16 MHz 18/19 MHz 22 MHz 25/26 MHz
2065.0 4146.0 6224.0 8294.0 12353.0 16528.0 18825.0 22159.0 25100.0
2079.0 4149.0 6227.0 8297.0 12356.0 16531.0 18828.0 22162.0 25103.0
2093.0 4417.0 6230.0   12359.0 16534.0 18831.0 22165.0 25106.0
2096.5   *6516.0   12362.0 16537.0 18834.0 22168.0 25109.0
2214.0       12365.0 16540.0 18837.0 22171.0 25112.0
          16543.0 18840.0 22174.0 25115.0
          16546.0 18843.0 22177.0 25118.0
* Authorized for Daytime Use Only
All frequencies in "kHz."

Shared HF-SSB Simplex Frequencies

In addition to the primary simplex frequencies above, there are a large number of frequencies in the 4 MHz and 8 MHz bands that may be used on a shared basis with fixed services ashore.

Shared Simplex Frequencies
4 MHz Band 8 MHz Band
4000.0 kHz 8101.0 kHz
4003.0 kHz 8104.0 kHz
4006.0 kHz 8107.0 kHz
4009.0 kHz 8110.0 kHz
4012.0 kHz 8113.0 kHz
4015.0 kHz 8116.0 kHz
4018.0 kHz 8119.0 kHz
4021.0 kHz 8122.0 kHz
4024.0 kHz 8125.0 kHz
4027.0 kHz 8128.0 kHz
4030.0 kHz 8131.0 kHz
4033.0 kHz 8134.0 kHz
4036.0 kHz 8137.0 kHz
4039.0 kHz 8140.0 kHz
4042.0 kHz 8143.0 kHz
4045.0 kHz 8146.0 kHz
4048.0 kHz 8149.0 kHz
4051.0 kHz 8152.0 kHz
4054.0 kHz 8155.0 kHz
4057.0 kHz 8158.0 kHz
4060.0 kHz 8161.0 kHz
---- 8164.0 kHz
---- 8167.0 kHz
---- 8170.0 kHz
---- 8173.0 kHz
---- 8176.0 kHz
---- 8179.0 kHz
---- 8182.0 kHz
---- 8185.0 kHz
---- 8188.0 kHz
---- 8191.0 kHz

Special Use Simplex Frequencies

In addition to the international frequencies listed above, individual nation states will often have other frequencies available for use for particular purposes or for use in particular geographic areas. An example would be in the United States there are additional 2 MHz simplex frequencies shown below:

Intership Safety and Operational Communications
Frequency Geographic Area
2003.0 kHz Great Lakes Only.
2782.0 kHz Mississippi River Working Frequency.
2082.5 kHz All Areas. Also Intership Non-Commercial Fishing.
2086.0 kHz Mississippi River Working Frequency
2093.0 kHz All Areas.
2142.0 kHz Pacific Coast, Daily, South of 42°N.
2203.0 kHz Gulf of Mexico. Also, Intership Non-Commercial Fishing.
2214.0 kHz All Areas.
2635.0 kHz ITU Regions 2-3 (ITU RR 4193). Not in FCC rules.
2638.0 kHz All Areas.
2670.0 kHz All Areas.
2738.0 kHz All Areas, Except Great Lakes. Shared with Aircraft.
2830.0 kHz Gulf of Mexico Only. Shared with Aircraft.
Business and Operational Frequencies
Frequency Geographic Area
2065.0 kHz All Areas.
2079.0 kHz All Areas.
2096.5 kHz All Areas.
3023.0 kHz Government shore, ship and aircraft stations for search and rescue coordination.
These 2 MHz SSB simplex radiotelephone frequencies are available for ships in or near U.S. waters.

Download all of the above MF/HF-SSB Simplex Frequency Tables

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