I was just wondering how important it is to configure the External gain on the Access point and SM units and which values would be the correct ones to use?
I found some values in the older configuration / user guides : Version 12.0.2 but I see the values got removed in later releases of the user guide so I'm not sure whether they're still valid or not?
PMP450 AP with stock connectorized Antenna : 17dBi PMP450 SM with LENS : 5dBi
Sure... the 450 system operates with ATPC, or Automatic Transmission Power Control. This means that the subscriber module (SM) will only put out enough Tx Power to achieve the target signal level at the Access Point (AP, or Base Station).
The SM relies on the operator to input the proper "External Gain" setting for the antenna being used in order to properly compensate the transmit power to achieve the desired RSL (Receive Signal Level) at the AP.
If the External Gain setting is set too high (i.e. you've made a mistake and put in 25 dBi gain instead of 15 dBi gain for the external reflector dish), then the radio will set its Tx Power artificially low, and may hit what it thinks is the regulatory limit for EIRP too early, resulting in a poor quality link.
If the External Gain setting is set too low (i.e. you set 5 dBi when the actual antenna is giving you 10 dBi gain), then the radio will be putting out more Tx Power than it needs to. This can result in creating unnecessary interference for other devices (i.e. creates noise in the band).
Yes, this applies to any frequency... in 3.65 it is especially important as there is a Listen-Before-Talk (LBT) requirement as well, which can affect the performance if this setting is incorrect.
Correct. For the original 3.65 GHz 450 SM, the internal gain value is 8 dBi.
The reflector dish adds 12 dBi (so in the software, the “External Gain” field in the software should be set to +12 dBi), and the total gain is 8 + 12 = 20 dBi.