Had a chance to test today and the findings are as I have previously observed on typical multi-STB installations.
#1 Test: Two STBs set to vertical polarity with switching power supplies connected to the same power strip (no ground on power supply AC/DC transformers). Two 3' coax cables each connected to one STB. Multi-meter voltage test between unloaded coax cables. Ground source is the plate cover screw.
STB 1: Center1 to Braid1 - 13.77Vdc
STB 2: Center2 to Braid2 - 13.81Vdc
Center1 to Center2 - 0Vdc
Center1 to Braid2 - 0Vdc
Center2 to Braid1 - 0Vdc
Center1 to Ground - 27.5Vac
Center2 to Ground - 27.6Vac
Braid1 to Ground - 27.5Vac
Braid2 to Ground - 27.6Vac
#2 Test: Two STBs set to vertical polarity with switching power supplies connected to the same power strip (no ground on power supply AC/DC transformers). Two 3' coax cables each connected to one STB and looping through dual ground block (connected to structure ground). Multi-meter voltage test between unloaded coax cables. Ground source is the plate cover screw.
STB 1: Center1 to Braid1 - 13.77Vdc
STB 2: Center2 to Braid2 - 13.81Vdc
Center1 to Center2 - 0Vdc
Center1 to Braid2 - 13.77Vdc
Center2 to Braid1 - 13.81Vdc
Center1 to Ground - 0Vac
Center2 to Ground - 0Vac
Braid1 to Ground - 0Vac
Braid2 to Ground - 0Vac
#3 Test: Two STBs set to vertical polarity with switching power supplies. STB 1 remains plugged into same power strip and STB 2 plugged into an extension cord running to an outlet on a different circuit breaker (no ground on power supply AC/DC transformers). Two 3' coax cables each connected to one STB and looping through dual ground block (connected to structure ground). Multi-meter voltage test between unloaded coax cables. Ground source is the plate cover screw.
STB 1: Center1 to Braid1 - 13.76Vdc
STB 2: Center2 to Braid2 - 13.80Vdc
Center1 to Center2 - 0Vdc
Center1 to Braid2 - 13.76Vdc
Center2 to Braid1 - 13.80Vdc
Center1 to Ground - 0Vac
Center2 to Ground - 0Vac
Braid1 to Ground - 0Vac
Braid2 to Ground - 0Vac
As you see by the above testing, there is only slight change when STB #2 was moved to another circuit breaker, but there is no interaction between the two circuits. This is what I would expect to observe when measuring voltages between two STBs at the coax cables disconnected from a dual LNBF. There would be a slight voltage drop due to the length of coax cables, but no interaction between the STBs
Why is voltage present beween your two coax cables where there shouldn't be. Try starting with the test #1 and #2 as above and observe if there is interaction between the two STBs when plugged into the same power strip without anything else attached. Then compare testing #1/#2 to the results of test #3. We can replace the damaged dual LNBF, but before installing, this voltage issue needs to be addressed.
#1 Test: Two STBs set to vertical polarity with switching power supplies connected to the same power strip (no ground on power supply AC/DC transformers). Two 3' coax cables each connected to one STB. Multi-meter voltage test between unloaded coax cables. Ground source is the plate cover screw.
STB 1: Center1 to Braid1 - 13.77Vdc
STB 2: Center2 to Braid2 - 13.81Vdc
Center1 to Center2 - 0Vdc
Center1 to Braid2 - 0Vdc
Center2 to Braid1 - 0Vdc
Center1 to Ground - 27.5Vac
Center2 to Ground - 27.6Vac
Braid1 to Ground - 27.5Vac
Braid2 to Ground - 27.6Vac
#2 Test: Two STBs set to vertical polarity with switching power supplies connected to the same power strip (no ground on power supply AC/DC transformers). Two 3' coax cables each connected to one STB and looping through dual ground block (connected to structure ground). Multi-meter voltage test between unloaded coax cables. Ground source is the plate cover screw.
STB 1: Center1 to Braid1 - 13.77Vdc
STB 2: Center2 to Braid2 - 13.81Vdc
Center1 to Center2 - 0Vdc
Center1 to Braid2 - 13.77Vdc
Center2 to Braid1 - 13.81Vdc
Center1 to Ground - 0Vac
Center2 to Ground - 0Vac
Braid1 to Ground - 0Vac
Braid2 to Ground - 0Vac
#3 Test: Two STBs set to vertical polarity with switching power supplies. STB 1 remains plugged into same power strip and STB 2 plugged into an extension cord running to an outlet on a different circuit breaker (no ground on power supply AC/DC transformers). Two 3' coax cables each connected to one STB and looping through dual ground block (connected to structure ground). Multi-meter voltage test between unloaded coax cables. Ground source is the plate cover screw.
STB 1: Center1 to Braid1 - 13.76Vdc
STB 2: Center2 to Braid2 - 13.80Vdc
Center1 to Center2 - 0Vdc
Center1 to Braid2 - 13.76Vdc
Center2 to Braid1 - 13.80Vdc
Center1 to Ground - 0Vac
Center2 to Ground - 0Vac
Braid1 to Ground - 0Vac
Braid2 to Ground - 0Vac
As you see by the above testing, there is only slight change when STB #2 was moved to another circuit breaker, but there is no interaction between the two circuits. This is what I would expect to observe when measuring voltages between two STBs at the coax cables disconnected from a dual LNBF. There would be a slight voltage drop due to the length of coax cables, but no interaction between the STBs
Why is voltage present beween your two coax cables where there shouldn't be. Try starting with the test #1 and #2 as above and observe if there is interaction between the two STBs when plugged into the same power strip without anything else attached. Then compare testing #1/#2 to the results of test #3. We can replace the damaged dual LNBF, but before installing, this voltage issue needs to be addressed.
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