Simplex vs. Semi-Duplex

[zerowatts]

As I understand it Simplex is just radio to radio correct? What is Semi-Duplex? Radio to radio + Repeater?

 

[dwh367]

As I understand it Simplex is just radio to radio correct? What is Semi-Duplex? Radio to radio + Repeater?

Simplex communications takes place on the same frequency. Semi-Duplex communications uses two frequencies. For example, when transmitting into an amateur radio repeater, you are transmitting on one frequency and listening on another. The repeater is "Full Duplex" meaning it can transmit and recieve at the same time. When we talk through a repeater, we are "semi-duplex" meaning we are either transmitting or receiving.

 

[DaveNF2G]

I don't think any variation on "duplex" applies to using a repeater. Simplex is direct radio-to-radio on one frequency. Duplex is direct radio-to-radio on two frequencies. Going through a repeater is radio-to-radio-to-radio, not duplex.

Full- and semi- are as you described.

 

[stevelton]

Yet another variation of semi-duplex is a method that some taxi companies use. Its simplex, but on 2 freqs. and no repeater. the base listens on one freq, the freq that the mobiles transmit. the mobiles listen on a different freq, the freq, the base transmits. This way the mobiles can only here the base, and not the other mobiles. It keeps the mobile to mobile 'chit chat' down, because the mobiles arent able to hear each other.
Steven

 

[VernM]

Stevelton, what you describe is a common repeater system. They all work that way, other than digital store-and-retransmit systems, which are slow and not very often used other than for a ham on foot using his vehicle to store-and-forward from a better antenna location.

 

[zerowatts]

Ok so radios that advertise as semi-duplex are in simpler terms just advertising that they are repeater capable?

Aside from all the advantages of having/using a repeater system there is no advantage to having a semi-duplex setup am I correct? We certainly can't be talking and receiving at the same time even with a repeater right?

 

[n5ims]

Here are some details on the three types of communications, with graphics. Type of Communication, Simplex, Semi Duplex, Duplex | IT Engineer's Blog, Malaysia Life Tech Blog

Many communications centers allow their dispatch operators to monitor the repeater's input channel while they transmit on the output channel (basically do full duplex). This allows field officers to interupt them in an emergency. Officers in the field often will hear both the input channel and dispatch operator, the dispatch operator can pause their communication and allow the emergency traffic to be heard. I've heard this called "Dispatch Interrupt", although this doesn't appear to be an official term.

Many systems have a "talk-around" channel defined into their radios where stations can communicate directly when out of range (or when there's a system failure). If both the talk-around and dispatch interrupt are in operation, the radios would be supporting simplex, semi-duplex, and full-duplex within the same system.

 

[DaveNF2G]

Stevelton, what you describe is a common repeater system. They all work that way, other than digital store-and-retransmit systems, which are slow and not very often used other than for a ham on foot using his vehicle to store-and-forward from a better antenna location.

No, what he describes is half-duplex. A repeater is an additional station that simultaneously retransmits signals onto another frequency for all to hear. Taxi companies do not typically use repeaters, for reasons stevelton mentioned.