Simplex or Duplex

[tdukes]

Hello,

I setup a backyard repeater that's not giving me a lot of range due to antenna height and numerous tall trees. In this location, I will never be able to be above the trees. I am also in a paid repeater group that is connected to myGMRS. I do not plan to compete against them but may try setting up a 'private' Allstar network with some friends in IL and WI and others that may want to connect. I have a VM running Allstar now and just need a radio to connect to it.

I'm a little fuzzy on this regarding connecting to a network like myGMRS.

So is a radio in a box, connected to a Pi, simplex even though it RXs and TXs on a repeater channel? What if that radio in a box is also connected to a repeater, does that make duplex?

Thanks!!

[KAF6045]

1 minute ago, tdukes said:

So is a radio in a box, connected to a Pi, simplex even though it RXs and TXs on a repeater channel? What if that radio in a box is also connected to a repeater, does that make duplex?

 

Duplex means the radio is transmitting on one frequency (467.xxx MHz for GMRS) and receives on the corresponding frequency (462.xxx MHz). Simplex means the radio is transmitting and receiving on the same frequency in the 462 MHz range (except for the now-permissible 0.5W ERP NFM channels 8-14, which are 467 MHz).

I really abhor the FCC channel number scheme which treats the simplex main channels and repeater as /separate entities/. As seen in a number of threads on this forum, it just leads to confusion (in the old days, one had a button on the radio that toggled between simplex and duplex on a given channel, and the channel was commonly identified by the .xxx portion of the frequency [one's license only authorized TWO of the eight main channels, so your channels A&B might not be the same as my A&B).

Channels 15-22 and 23-30 (aka: rp15-rp22, 15r-22r, and other naming schemes) receive on the 462MHz, with the result that people with simplex only radios (FRS) or tuned to simplex 15-22 still receive the output from repeaters, but can not transmit to the repeater.

 

Most R-Pi configurations (I'm only accustomed to Amateur Pi-Star usage) are simplex from radio to Pi-Star -- only one side can transmit at a time (a true repeater is receiving on 467 and SIMULTANEOUSLY sending what it received back out on 462). If the R-Pi side is transmitting, it will not hear anything you try to send until the board goes silent (toggles to Listening mode). For Amateur, there ARE boards that support duplex mode -- they have two antenna on the board (not to be confused with dual-band boards, which can be configured for 2m or 70cm usage).

Take into account that these boards run VERY LOW power... <50mW is not uncommon, I don't think I've heard of any that gets as high as 100mW! Strangely, my radios can pick up my Pi-Star system from down the block (500 feet or so), but it won't receive my transmissions, even on high power. Probably evidence of how much more sensitive the Kenwood/Icom HTs are compared to an SoC radio chip on top of a potentially RF-noisy processor board.

Once your signal hits the internet, simplex/duplex is irrelevant -- it only applies to the link from radios to node and node to radios, and most R-Pi nodes are probably running simplex. If someone has managed to connect the R-Pi to an actual repeater, then it is duplex at that repeater. If it is linked to another simplex node, well -- it is again simplex.