[R-390] Filter Protection: LND150 installed and working

[David Wise]

?While I had the IF deck out to repair "Intermittent Noisy Drop In Gain", I installed an LND150.  I put it on a Keystone #847 miniature 3-position terminal strip, which has two terminals and one non-terminal mounting ring.  I mounted it next to the XV501 shield wall using the pre-existing screw which was already securing a ground lug for a bypass cap.  I moved the low end of C553 from the bandwidth switch to the LND150 drain, and connected the LND150 gate to the switch.  The source goes to the gate via a 1K 1/8W resistor.  I did all the terminal strip soldering before mounting it, so as not to melt the plastic insulating strip I placed behind it.


It works fine.  Receiver gain is normal until C553 is shorted, then it drops to nil; but the filter is unharmed, and performance returns to normal when the short is removed.


Why the resistor?  To ensure the short-circuit (current, power) is at most (1mA, 200mW).  The LND150 barely breaks a sweat.


Dave Wise