Help Understanding Semtech Packet Forwarder Configuration

I’m wondering how a LoRaWAN gateway could be used to transmit a packet on any 1 of 8 channels instead of 1 of 4 channels? I’m trying to understand a LoRaWAN network I came across that is transmitting data using 8 channel gateways (and transmitting on all 8 125khz channels), but has a packet forwarder config where radio_0 is “tx_enable”: true and radio_1 is ““tx_enable”: false”

What config would I use to enable transmit from both radios in the concentrator?

Ex: packet_forwarder/global_conf.json.US902.basic at master · Lora-net/packet_forwarder · GitHub

This has always confused me honestly. How can an 8 channel gateway/network ever transmit on all 8 125khz channels (US915 band plan for example) when the packet forwarder “tx_enable” parameter is always set to true for one rf chain and false for the other?

Hopefully a simple thing I’m misunderstanding. Thanks!

In the gateways I know, the TX of the second chip is always disabled. If you want to transmit with two transmitters using the same antenna you need a power combiner. You have to be very careful not to blow up your 1. receiver while transmitting with the second channel.
Additionally gateways should transmit only very seldom, so a second transmitter doesn’t make sense - but a second receiver to monitor more channels. It is no problem to split a received signal. If you look into the circuit drawings of Semtech you can see how this is done.
If you love your gateway don’t activate the second transmitter without knowing very well what you are doing.

For transmission the frequencies used are not configured in the packet forwarder. In newer packet forwarders the upper and lower limit might be specified but that is all. The back-end specifies which frequency will be used for transmission by the one radio that is allowed to transmit. As @wolfp explains you would need different hardware to allow both radios to transmit.