MF & HF-SSB Duplex Channels

We have already covered the recognized MF/HF Simplex Frequencies and their importance in ship to ship and distress communications. Here we will concentrate on the HF - Duplex Channels used in typical ship to shore communications.

In its simplest terms, a Duplex Channel is simply (2) different simplex frequencies paired together to form a channel. (1) frequency is used to transmit and the other is used to receive. As an example, If you select ITU Channel 401 on your HF-SSB to communicate on your radio, you will be transmitting on 4065.0 kHz and receiving on 4357.0 kHz.

It is important to note that Marine HF-SSB radios (much like the Marine VHF,) are not true duplex radios, but better described as "half-duplex." This means that the radio can only be in one of two states: either a transmitter or a receiver, it cannot be in both states simultaneously unless you have special equipment installed along with your radio. Most radios are toggled between these two states (transmit and receive) by the push to talk button. This however does not change the fact that the use of different paired frequencies are known as duplex channels.

Are there any advantages to the use of duplex channels? Surprisingly, very few. However, these advantages are major from the perspective of a coast station. They allow for "repeater" usage; which often extends the range of communications by allowing more transmit power to be used and also allows for the ability to locate the antenna in a more advantageous location. This being the typical reasoning behind the usage of duplex channels in ship to shore communications.

Frequency Bands

Like the simplex frequencies, the HF Marine SSB duplex frequencies are grouped into frequency bands. There are currently 9 bands that have been allocated for marine service:

2 MHz 4 MHz 6 MHz 8 MHz 12 MHz 16 MHz 18 MHz 22 MHz 25 MHz

We will ignore the 2 MHZ frequencies, due to their limited range, leaving us with 8 frequency bands that most duplex channels fall into.

HF Duplex Channel Pairs

In the dropdowns below, we have provided a complete list of all internationally accepted ITU standard frequency pairs. These frequency pairs have been broken down by their frequency bands and identified by their channel number.

In your typical marine HF-SSB radio a large number of these channels are pre-programed into the set by the manufacturer. They also have memory space available to allow the user to enter others.

Open Down Arrow ITU 4 MHz Channels

4 MHz Duplex Channel Frequency Pairs
ITU Channel No. Coast Transmit / Ship Receive Ship Transmit / Coast Receive
401 4357.0 kHz 4065.0 kHz
402 4360.0 kHz 4068.0 kHz
403 4363.0 kHz 4071.0 kHz
404 4366.0 kHz 4074.0 kHz
405 4369.0 kHz 4077.0 kHz
406 4372.0 kHz 4080.0 kHz
407 4375.0 kHz 4083.0 kHz
408 4378.0 kHz 4086.0 kHz
409 4381.0 kHz 4089.0 kHz
410 4384.0 kHz 4092.0 kHz
411 4387.0 kHz 4095.0 kHz
412 4390.0 kHz 4098.0 kHz
413 4393.0 kHz 4101.0 kHz
414 4396.0 kHz 4104.0 kHz
415 4399.0 kHz 4107.0 kHz
416 4402.0 kHz 4110.0 kHz
417 4405.0 kHz 4113.0 kHz
418 4408.0 kHz 4116.0 kHz
419 4411.0 kHz 4119.0 kHz
420 4414.0 kHz 4122.0 kHz
*421 4417.0 kHz 4125.0 kHz
422 4420.0 kHz 4128.0 kHz
423 4423.0 kHz 4131.0 kHz
424 4426.0 kHz 4134.0 kHz
425 4429.0 kHz 4137.0 kHz
426 4432.0 kHz 4140.0 kHz
427 4435.0 kHz 4143.0 kHz
428 4351.0 kHz (Varies)
429 4354.0 kHz (Varies)
*This channel is not recommended due to the use of the 4 MHz Distress, Safety, & Calling frequency within the channel pair.

Open Down Arrow ITU 6 MHz Channels

6 MHz Duplex Channel Frequency Pairs
ITU Channel No. Coast Transmit / Ship Receive Ship Transmit / Coast Receive
601 6501.0 kHz 6200.0 kHz
602 6504.0 kHz 6203.0 kHz
603 6507.0 kHz 6206.0 kHz
604 6510.0 kHz 6209.0 kHz
605 6513.0 kHz 6212.0 kHz
*606 6516.0 kHz 6215.0 kHz
607 6519.0 kHz 6218.0 kHz
608 6522.0 kHz 6221.0 kHz
*This channel is not recommended due to the use of the 6 MHz Distress, Safety, & Calling frequency within the channel pair.

Open Down Arrow ITU 8 MHz Channels

8 MHz Duplex Channel Frequency Pairs
ITU Channel No. Coast Transmit / Ship Receive Ship Transmit / Coast Receive
801 8719.0 kHz 8195.0 kHz
802 8722.0 kHz 8198.0 kHz
803 8725.0 kHz 8201.0 kHz
804 8728.0 kHz 8204.0 kHz
805 8731.0 kHz 8207.0 kHz
806 8734.0 kHz 8210.0 kHz
807 8737.0 kHz 8213.0 kHz
808 8740.0 kHz 8216.0 kHz
809 8743.0 kHz 8219.0 kHz
810 8746.0 kHz 8222.0 kHz
811 8749.0 kHz 8225.0 kHz
812 8752.0 kHz 8228.0 kHz
813 8755.0 kHz 8231.0 kHz
814 8758.0 kHz 8234.0 kHz
815 8761.0 kHz 8237.0 kHz
816 8764.0 kHz 8240.0 kHz
817 8767.0 kHz 8243.0 kHz
818 8770.0 kHz 8246.0 kHz
819 8773.0 kHz 8249.0 kHz
820 8776.0 kHz 8252.0 kHz
821 8779.0 kHz 8255.0 kHz
822 8782.0 kHz 8258.0 kHz
823 8785.0 kHz 8261.0 kHz
824 8788.0 kHz 8264.0 kHz
825 8791.0 kHz 8267.0 kHz
826 8794.0 kHz 8270.0 kHz
827 8797.0 kHz 8273.0 kHz
828 8800.0 kHz 8276.0 kHz
829 8803.0 kHz 8279.0 kHz
830 8806.0 kHz 8282.0 kHz
831 8809.0 kHz 8285.0 kHz
832 8812.0 kHz 8288.0 kHz
*833 8291.0 kHz 8291.0 kHz
834 8707.0 kHz (Varies)
835 8710.0 kHz (Varies)
836 8713.0 kHz (Varies)
837 8716.0 kHz (Varies)
*This channel is not recommended due to the use of the 8 MHz Distress, Safety, & Calling frequency within the channel pair.

Open Down Arrow ITU 12 MHz Channels

12 MHz Duplex Channel Frequency Pairs
ITU Channel No. Coast Transmit / Ship Receive Ship Transmit / Coast Receive
1201 13,077.0 kHz 12,230.0 kHz
1202 13,080.0 kHz 12,233.0 kHz
1203 13,083.0 kHz 12,236.0 kHz
1204 13,086.0 kHz 12,239.0 kHz
1205 13,089.0 kHz 12,242.0 kHz
1206 13,092.0 kHz 12,245.0 kHz
1207 13,095.0 kHz 12,248.0 kHz
1208 13,098.0 kHz 12,251.0 kHz
1209 13,101.0 kHz 12,254.0 kHz
1210 13,104.0 kHz 12,257.0 kHz
1211 13,107.0 kHz 12,260.0 kHz
1212 13,110.0 kHz 12,263.0 kHz
1213 13,113.0 kHz 12,266.0 kHz
1214 13,116.0 kHz 12,269.0 kHz
1215 13,119.0 kHz 12,272.0 kHz
1216 13,122.0 kHz 12,275.0 kHz
1217 13,125.0 kHz 12,278.0 kHz
1218 13,128.0 kHz 12,281.0 kHz
1219 13,131.0 kHz 12,284.0 kHz
1220 13,134.0 kHz 12,287.0 kHz
*1221 13,137.0 kHz 12,290.0 kHz
1222 13,140.0 kHz 12,293.0 kHz
1223 13,143.0 kHz 12,296.0 kHz
1224 13,146.0 kHz 12,299.0 kHz
1225 13,149.0 kHz 12,302.0 kHz
1226 13,152.0 kHz 12,305.0 kHz
1227 13,155.0 kHz 12,308.0 kHz
1228 13,158.0 kHz 12,311.0 kHz
1229 13,161.0 kHz 12,314.0 kHz
1230 13,164.0 kHz 12,317.0 kHz
1231 13,167.0 kHz 12,320.0 kHz
1232 13,170.0 kHz 12,323.0 kHz
1233 13,173.0 kHz 12,326.0 kHz
1234 13,176.0 kHz 12,329.0 kHz
1235 13,179.0 kHz 12,332.0 kHz
1236 13,182.0 kHz 12,335.0 kHz
1237 13,185.0 kHz 12,338.0 kHz
1238 13,188.0 kHz 12,341.0 kHz
1239 13,191.0 kHz 12,344.0 kHz
1240 13,194.0 kHz 12,347.0 kHz
1241 13,197.0 kHz 12,350.0 kHz
*This channel is not recommended due to the use of the 12 MHz Distress, Safety, & Calling frequency within the channel pair.

Open Down Arrow ITU 16 MHz Channels

16 MHz Duplex Channel Frequency Pairs
ITU Channel No. Coast Transmit / Ship Receive Ship Transmit / Coast Receive
1601 17,242.0 kHz 16,360.0 kHz
1602 17,245.0 kHz 16,363.0 kHz
1603 17,248.0 kHz 16,366.0 kHz
1604 17,251.0 kHz 16,369.0 kHz
1605 17,254.0 kHz 16,372.0 kHz
1606 17,257.0 kHz 16,375.0 kHz
1607 17,260.0 kHz 16,378.0 kHz
1608 17,263.0 kHz 16,381.0 kHz
1609 17,266.0 kHz 16,384.0 kHz
1610 17,269.0 kHz 16,387.0 kHz
1611 17,272.0 kHz 16,390.0 kHz
1612 17,275.0 kHz 16,393.0 kHz
1613 17,278.0 kHz 16,396.0 kHz
1614 17,281.0 kHz 16,399.0 kHz
1615 17,284.0 kHz 16,402.0 kHz
1616 17,287.0 kHz 16,405.0 kHz
1617 17,290.0 kHz 16,408.0 kHz
1618 17,293.0 kHz 16,411.0 kHz
1619 17,296.0 kHz 16,414.0 kHz
1620 17,299.0 kHz 16,417.0 kHz
*1621 17,302.0 kHz 16,420.0 kHz
1622 17,305.0 kHz 16,423.0 kHz
1623 17,308.0 kHz 16,426.0 kHz
1624 17,311.0 kHz 16,429.0 kHz
1625 17,314.0 kHz 16,432.0 kHz
1626 17,317.0 kHz 16,435.0 kHz
1627 17,320.0 kHz 16,438.0 kHz
1628 17,323.0 kHz 16,441.0 kHz
1629 17,326.0 kHz 16,444.0 kHz
1630 17,329.0 kHz 16,447.0 kHz
1631 17,332.0 kHz 16,450.0 kHz
1632 17,335.0 kHz 16,453.0 kHz
1633 17,338.0 kHz 16,456.0 kHz
1634 17,341.0 kHz 16,459.0 kHz
1635 17,344.0 kHz 16,462.0 kHz
1636 17,347.0 kHz 16,465.0 kHz
1637 17,350.0 kHz 16,468.0 kHz
1638 17,353.0 kHz 16,471.0 kHz
1639 17,356.0 kHz 16,474.0 kHz
1640 17,359.0 kHz 16,477.0 kHz
1641 17,362.0 kHz 16,480.0 kHz
1642 17,365.0 kHz 16,483.0 kHz
1643 17,368.0 kHz 16,486.0 kHz
1644 17,371.0 kHz 16,489.0 kHz
1645 17,374.0 kHz 16,492.0 kHz
1646 17,377.0 kHz 16,495.0 kHz
1647 17,380.0 kHz 16,498.0 kHz
1648 17,383.0 kHz 16,501.0 kHz
1649 17,386.0 kHz 16,504.0 kHz
1650 17,389.0 kHz 16,507.0 kHz
1651 17,392.0 kHz 16,510.0 kHz
1652 17,395.0 kHz 16,513.0 kHz
1653 17,398.0 kHz 16,516.0 kHz
1654 17,401.0 kHz 16,519.0 kHz
1655 17,404.0 kHz 16,522.0 kHz
1656 17,407.0 kHz 16,525.0 kHz
*This channel is not recommended due to the use of the 16 MHz Distress, Safety, & Calling frequency within the channel pair.

Open Down Arrow ITU 18 MHz Channels

18 MHz Duplex Channel Frequency Pairs
ITU Channel No. Coast Transmit / Ship Receive Ship Transmit / Coast Receive
1801 19,755.0 kHz 18,780.0 kHz
1802 19,758.0 kHz 18,783.0 kHz
1803 19,761.0 kHz 18,786.0 kHz
1804 19,764.0 kHz 18,789.0 kHz
1805 19,767.0 kHz 18,792.0 kHz
1806 19,770.0 kHz 18,795.0 kHz
1807 19,773.0 kHz 18,798.0 kHz
1808 19,776.0 kHz 18,801.0 kHz
1809 19,779.0 kHz 18,804.0 kHz
1810 19,782.0 kHz 18,807.0 kHz
1811 19,785.0 kHz 18,810.0 kHz
1812 19,788.0 kHz 18,813.0 kHz
1813 19,791.0 kHz 18,816.0 kHz
1814 19,794.0 kHz 18,819.0 kHz
1815 19,797.0 kHz 18,822.0 kHz
 

Open Down Arrow ITU 22 MHz Channels

22 MHz Duplex Channel Frequency Pairs
ITU Channel No. Coast Transmit / Ship Receive Ship Transmit / Coast Receive
2201 22,696.0 kHz 22,000.0 kHz
2202 22,699.0 kHz 22,003.0 kHz
2203 22,702.0 kHz 22,006.0 kHz
2204 22,705.0 kHz 22,009.0 kHz
2205 22,708.0 kHz 22,012.0 kHz
2206 22,711.0 kHz 22,015.0 kHz
2207 22,714.0 kHz 22,018.0 kHz
2208 22,717.0 kHz 22,021.0 kHz
2209 22,720.0 kHz 22,024.0 kHz
2210 22,723.0 kHz 22,027.0 kHz
2211 22,726.0 kHz 22,030.0 kHz
2212 22,729.0 kHz 22,033.0 kHz
2213 22,732.0 kHz 22,036.0 kHz
2214 22,735.0 kHz 22,039.0 kHz
2215 22,738.0 kHz 22,042.0 kHz
2216 22,741.0 kHz 22,045.0 kHz
2217 22,744.0 kHz 22,048.0 kHz
2218 22,747.0 kHz 22,051.0 kHz
2219 22,750.0 kHz 22,054.0 kHz
2220 22,753.0 kHz 22,057.0 kHz
2221 22,756.0 kHz 22,060.0 kHz
2222 22,759.0 kHz 22,063.0 kHz
2223 22,762.0 kHz 22,066.0 kHz
2224 22,765.0 kHz 22,069.0 kHz
2225 22,768.0 kHz 22,072.0 kHz
2226 22,771.0 kHz 22,075.0 kHz
2227 22,774.0 kHz 22,078.0 kHz
2228 22,777.0 kHz 22,081.0 kHz
2229 22,780.0 kHz 22,084.0 kHz
2230 22,783.0 kHz 22,087.0 kHz
2231 22,786.0 kHz 22,090.0 kHz
2232 22,789.0 kHz 22,093.0 kHz
2233 22,792.0 kHz 22,096.0 kHz
2234 22,795.0 kHz 22,099.0 kHz
2235 22,798.0 kHz 22,102.0 kHz
2236 22,801.0 kHz 22,105.0 kHz
2237 22,804.0 kHz 22,108.0 kHz
2238 22,807.0 kHz 22,111.0 kHz
2239 22,810.0 kHz 22,114.0 kHz
2240 22,813.0 kHz 22,117.0 kHz
2241 22,816.0 kHz 22,120.0 kHz
2242 22,819.0 kHz 22,123.0 kHz
2243 22,822.0 kHz 22,126.0 kHz
2244 22,825.0 kHz 22,129.0 kHz
2245 22,828.0 kHz 22,132.0 kHz
2246 22,831.0 kHz 22,135.0 kHz
2247 22,834.0 kHz 22,138.0 kHz
2248 22,837.0 kHz 22,141.0 kHz
2249 22,840.0 kHz 22,144.0 kHz
2250 22,843.0 kHz 22,147.0 kHz
2251 22,846.0 kHz 22,150.0 kHz
2252 22,849.0 kHz 22,153.0 kHz
2253 22,852.0 kHz 22,156.0 kHz
 

Open Down Arrow ITU 25 MHz Channels

25 MHz Duplex Channel Frequency Pairs
ITU Channel No. Coast Transmit / Ship Receive Ship Transmit / Coast Receive
2501 26,145.0 kHz 25,070.0 kHz
2502 26,148.0 kHz 25,073.0 kHz
2503 26,151.0 kHz 25,076.0 kHz
2504 26,154.0 kHz 25,079.0 kHz
2505 26,157.0 kHz 25,082.0 kHz
2506 26,160.0 kHz 25,085.0 kHz
2507 26,163.0 kHz 25,088.0 kHz
2508 26,166.0 kHz 25,091.0 kHz
2509 26,169.0 kHz 25,094.0 kHz
2510 26,172.0 kHz 25,097.0 kHz
 

Download the above HF Duplex Channel Tables 4 to 25 MHz

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