[hpsdr] LTC2208 input, a warning

[lstoskopf at cox.net]

I'm cross posting this to this list and QS1R list although not an issue on Mercury unless you mess around in it.

I'm a very happy user of the QS1R and the GUI is out of this world.  I wanted to use it as a 2nd receiver for the Orion.  Luckily TT put an RF out just after the RX input filters and I simply plugged a cable there, into one of the Z10000 buffer amps (google that) using a AD8007 as a Hi-Z buffer with 9 volt to the amp, gain 6 and a pad after, and the output to the spare connector on the back of the rig.  What could possibly go wrong.  Worked great and the AD8007 provided a safety buffer.  Or should I say, worked great for a while.

One day the SW came up "Buffer overflow" and the clipping light came on.  After trying several different computers with the same result, Phil C. asked me to send it back as I had blown the LTC2208.  It is on the way back fixed.

I had forgotten that the max input is Vdd +0.3 volts, not the maximum voltage swing with power applied!  Since I picked the supply voltage for the buffer from the Orion, the buffer could easily exceed 0.3 volts and if the QS1R wasn't turned on yet and invitation to blow.  Clipping diodes won't help there.  You need something tied to the QS1R supply.  Phil's input board will take care of that, but in the interim take care.

N0UU