# What's the difference between national calling frequency and national simplex calling frequency in the 2m and 70cm band plans published by ARRL?

On the 2 meter and 70 centimeter band plans published by the ARRL, what is the difference in intended use between the calling frequencies (144.200, 432.10 MHz) and the simplex calling frequencies (146.52, 446.00 MHz)?

• Note that this is complicated above Line A on 70cm because simplex calling is off-limits, but the calling frequency is available. I'm not sure what the regional standards are, but a local group I was involved with used 432.1MHz for FM calling in Ohio due to Line A. – user2943160 Jul 11 '16 at 6:54

The simplex calling frequencies (146.520/446.000 Mhz) are intended for FM simplex communication, while the other pair (144.200/432.100) are for SSB. In general use, the term "simplex" implies FM modulation since FM is commonly used in both simplex and duplex operation. SSB, CW, and other modes are generally used for longer distance, simplex-only communication.

This answer is based on the discussion I generated from posting this question on the Amateur Radio G+ community.

• Almost... 144.200 are for SSB and 146.250 is for FM. If you try to give a call on 146.250 on SSB your not likely to get much response. – buzzsawddog Feb 17 '14 at 15:48
• Ah yes, you are correct. I have the frequencies in my answer backwards from the question. I'll fix them. – Andrew N5ITM Feb 17 '14 at 16:07
• @buzzsawddog: You do mean 146.520, right? – PearsonArtPhoto Feb 17 '14 at 16:17
• doh... yeah sorry about that. – buzzsawddog Feb 19 '14 at 2:15

144.200/432.100 are intended for SSB Modulation.

146.520/446.000 are intended for FM Modulation.

• According to the ARRL band plan, FM Simplex Calling on 70cm is at 446.000 Mhz, not 446.200. (More generally, when it comes to fixing minor errors, it's better to either leave a comment on / edit the incorrect answer, rather than post a entirely separate answer as a standalone reply.) – Trevor Johns May 6 '15 at 3:12
• @TrevorJohns You could have: eddied the incorrect answer/typo. – buzzsawddog May 7 '15 at 15:39
• At the time of adding my answer I felt the other question was wrong and had to much fluff in it. To avoid an edit war it is often easier to write a new answer ;-) – buzzsawddog May 7 '15 at 15:42

Correction. Simplex is a mode of communication regardless of frequency band or modulation being used. Simplex in Amateur Radio is one way communication at a time between two communicating stations. When simultaneous transmission is used with capable equipment, it's called full duplex, meaning both stations can transmit and receive at the same time. There are other modes of communication as defined by the data communications world outside of Amateur Radio. Simplex by their definition is a device transmitting in one direction only, not able to reverse direction. Half duplex is a single transmission one way at a time, but is able to reverse direction. You could say Amateur Radio Simplex is really half duplex communication.

• I definitely agree with the last sentence of this. – SDsolar Apr 26 '18 at 19:49

Simplex implies transmission and reception on the same frequency without using a repeater. The band plan specifies that no repeaters are ever to transmit or receive on calling frequencies, nor should other operating modes, such as cross-band communication or remote control use them. In addition, it is expected that you can make initial contact on the calling frequency, but that you subsequently agree with each other to move the conversation to an alternative frequency (if you are going to speak to each other for more than a few minutes) to keep the calling frequency free for others' use.