I have just had two PTP820S 1+1 links installed, and during the alignment process, it was noted that the primary and secondary have an approximate dBm differnece of 3-6dBm.
So for example sake, I have the Primary talking to the other Primary, RSSI at each end will br approx -45dBm
When a Primary on either end is talking to a Secondary, the RSSI at each end will increase to approx -48dBm
When both Seondary units of the link communicate, the RSSI at each end increase again, up to around -51dBm
Is this normal play for the PTP820s, as they both are directly connected to the antenna via a coupler, operating the 11 GHz range.
Does the coupler deliberatly have a 3dBm loss for the Secondary?
The coupler is asymmetrical. The coupler is optimized for the PRI port. The tradeoff is that the SEC port has much more loss than the PRI port. Asymetric mediation devices are used for challenging links where the PRI ODU to PRI ODU link must have the lowest losses possible.
If the PRI ODU fails, the SEC ODU will take over, but the assumption is that the PRI ODU is repaired as quickly as possible, and that the link will revert to the PRI ODU automatically as soon as the PRI ODU is repaired.
(In other words, the link will spend the majority of its time with PRI ODU at one end talking with PRI ODU at the other end.)