Topic: E-Field amp and pre-amp build

[miraculon]

I finished the E-Field amp/pre today and did some preliminary testing. The first attempt was "no joy", seemed almost dead with about <10mV of noise.

After reviewing the schematic, and making the observation that there was no output on any of the three test points, it had to be common to all three circuits. It turned out that the output of the MCP6292 at pin 7 was stuck high at 5V. It should have been sitting at the half-rail of 2.5.

I somehow managed to create a solder short with some errant solder paste when I hot-air re-flow soldered the part. I completely removed it, cleaned the pads and re-soldered it. Voila, nominal 2.5V on pin 7. Results look much better, but I need to learn how to "drive" it using Cutty's gain setting thread here in the forum.

Greg H.

[miraculon]

I finally found my scope probes and started digging into why things didn't seem to be working correctly.

Based on prior experience with the RED mag-field amp, I expected the noise to scale up and down with the gain pot and it was still very low amplitude, with no change due to the gain control.  The IC leads looked good under a magnifier, and I even checked for shorts with the DMM and it looked OK.

I saw where some solder paste was sticking out from underneath some of the SOIC PGA chips. Looking at the layout, IC1, IC3 and IC5 have exposed vias under the IC location. I took a guess that some of the solder paste must be shorting these via pads underneath the IC.

After I removed, cleaned the pads and re-soldered the leads I rechecked the amp again. Now the noise scales with the gain pot. I have it up and running temporarily, waiting for the housings.

So, make sure that you don't have any solder paste that can sneak under IC1, IC3 or IC5! I don't know which one it was, but I re-did all three to be sure.

Greg
 

[JonathanW]

Good to hear!  The more E-field, the merrier

[miraculon]

The housing for the amplifier came and I installed the board yesterday.

I built up a housing for the antenna, using Cutty's "floor flange" concept but I mounted the antenna in the rafters. I originally had found a quiet area with my VLF radio and headphones. I brought out the laptop to the garage and put it on the signals page while trying other locations.

The strike indications dramatically increased when I raised the antenna up further into the rafters. (I was down low at the top of the wall) Surprisingly, the noise didn't seem to change so it looked like the best place. The E-Field is approximately on the same level as my H-Field loops.

I'll attach a couple of photos. It seems to be working great.

I also increased the antenna wire to 200mm length.

Greg H