Bias-t & LNA

[prcguy]

I have zero continuity between A and B on my side. Also look like it is epoxy sealed. Hard to say but from what I see from my tests I think my unit is bad.

Put 12VDC across A and B then touch 1 or 2 to 12V + and you should hear a faint click. If you ohm out the SMA connectors you should see it changes when you put 12V to 1 or 2.

 

[Pape]

Did try that, guess I screwed. How did you find that ? got the schematic or something ?
Thank for the info.
Indeed latching.

 

[prcguy]

Did try that, guess I screwed. How did you find that ? got the schematic or something ?
Thank for the info.
Indeed latching.

I've used a lot of these in my career and have seen the various ways they can be switched.

 

[Ubbe]

How does the latching works, it doesn't have connection between any SMA when the 12VDC are removed from +A and - B ?

/Ubbe

 

[Pape]

it is latching in 2 modes and remain latched in place when the power is removed.
Mode 1 is J1 and J4 together and J2 and J3 together
Mode 2 is J1 and J2 together and J3 and J4 together

It is good to add or remove device inline, example a filter.

 

[Ubbe]

OK, so cannot be used to bridge a preamp without running a second wire, and a third, up the coax as it has no fail safe mode.

Or use a bridge rectifier for the relay and preamp and then a diode in one direction to one control pin and a diode in the other direction to the other control pin and then switch polarity of the 12V at the bias-T.

Will probably need a 470uF reservoir capacitor on the bridge rectifier to hold a steady 12V during the polarity switch.

Probably better to buy a fail safe relay that configures the connection to bypass the preamp at power loss.

/Ubbe

 

[Pape]

For sure it will not meet the intended purpose but does fit some other idea I have.

 

[Ubbe]

I believe someone made an antenna switch up at the antennas using a latch relay. I think it involved using a diode rectifier to always power the relay with the correct 12V polarity and then a capacitor in series with the latch control pins that would make a pulse to the control pins when the polarity where switched at the bias-T and then the 12V could be removed from the coax, or still power a preamp.

/Ubbe