MF & HF-SSB Simplex Frequencies
Simplex frequencies whether MF, HF, or VHF are primarily used for distress, safety, hailing, ship to ship, and also for ship to shore communications. So why is it that duplex channels can’t be used for ship to ship communications? Well, technically they can. The problem is that it would require completely different equipment than today's common HF Transceiver found aboard most vessels.
Let's take a look at what happens when (2) vessels try to communicate on a common duplex channel. You can choose any ITU channel that you wish, but for this example we will pick channel 601.
So you are cruising along in Penobscot Bay and you call a friend on 6215.0 kHz who is, let’s say a couple of hundred miles south of Bermuda. After making contact, you both agree to switch to 601 to talk. So you both dial up channel 601 on your HF radios and here is what your frequency selection would look like:
ITU Channel 601 |
||||
|---|---|---|---|---|
| Your Boat | The Other Boat | |||
| You Xmit | You Recv | They Xmit | They Recv | |
| 6200.0 kHz | 6501.0 kHz | 6200.0 kHz | 6501.0 kHz | |
You are both transmitting on 6200.0 kHz, but you are both listening on 6501.0 kHz neither one of you are listening on 6200.0 kHz. So no one 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 601 the frequencies are reversed. They are transmitting on 6501.0 kHz and listening on 6200.0 kHz
ITU Channel 601 |
||||
|---|---|---|---|---|
| Your Boat | Public Coast Station | |||
| You Xmit | You Recv | They Xmit | They Recv | |
| 6200.0 kHz | 6501.0 kHz | 6501.0 kHz | 6200.0 kHz | |
This brings us back again to the use of simplex frequencies for ship to ship communications.
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." |
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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. | |
