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  1. drpappy

    Screen grounding

    From what I've seen, in general it is better to try attaching shield at both ends. The logic I've seen is to lift the noisey end to decouple it. Connecting at one end only creates more of a Faraday cage, where you want no current flow. But if you want a magnetic shield for higher frequencies...
  2. drpappy

    Standard Workmanship Standards

    [Lockheed] Martin Marrietta used to publish general electronics sub-assembly info called Workmanship Standards, but that was more than ten years ago. It had the color photos, accept-reject, etc. -goog luck
  3. drpappy

    back to engineering

    I don't know the life cycle of your product, but as with many things, manufacturing is done mainly with low cost in mind. Consumables and service has been the big ticket for at least ten years now. Stay meticulous in your work, and concentrate on being in the right place at the right time...
  4. drpappy

    Filtering noise on tip ring line

    Thanks. I did try lifting the drain wire to the gnd, but no help. In about a week, I'm going to try DC blocking caps like skogsgurra talked about on a different thread. Although, I don't know how they will impact CMRR.
  5. drpappy

    Puzzling Pulse Transformer output

    I was expecting to get flamed for such a dumb post; so I'll do it myself: As already mentioned above in the first posts, increasing the voltage swing can make saturation worse, not better. This is regardless if it's a pulse transformer or not. Although what I did notice on the bench was that...
  6. drpappy

    Puzzling Pulse Transformer output

    Can you increase the amplitude of the pulse? If so, the frequency response of the transformer may be a little better. Perhaps feed a signal generator into the transformer and see how it responds in the MHz range.
  7. drpappy

    Filtering noise on tip ring line

    It's one modem to another using a dedicated twisted pair, and is on all the time. I think the higher freq noise is riding in on 60Hz. This is because you can attenuate it just enough with an additional transformer (with less bandwidth, no DC; i.e. cheaper), and it seems to help, or at least...
  8. drpappy

    Filtering noise on tip ring line

    Thanks. I was a little weary of shunting the tip and ring lines to ground with caps, thinking about ground loops. I wonder if just bridging from tip to ring using capacitors or inductors (for 60Hz noise) would work? The signal is FSK. I know the 60Hz is common mode, and should cancel, but...
  9. drpappy

    Filtering noise on tip ring line

    I have a floating tip ring line that is fed into a transformer on my telephone device. The output of the transformer is referenced to ground. I can filter the noise from the output side with an active bandpass filter. However... My question is: How do I put the filter(s) on the floating...
  10. drpappy

    When Does a Fuse Catch on Fire?

    I've never used them, but there's those ceramic fuses filled with sand to dampen the burning.
  11. drpappy

    Current limiting the output of a power supply.

    Yes, our big accountants switched us to lighter gel cels that you can't add water back in. The typical current is 9Amps [Fluke DC current probe]. I'm shying away from adding more wire. Our safety guys would hari-kari; can't have that. I checked the repair records on the RF load and the DC...
  12. drpappy

    Current limiting the output of a power supply.

    ...Scotty, Have you been getting decent life out of your gel cels lately? The old lead calciums lasted 15yrs I hear. ...IRstuff, the fuses are'nt protecting my 0.2"/10A traces. Someone suggested adding more wire in parallel! ...itsmoked, niice I had been thinking of something similar but...
  13. drpappy

    Current limiting the output of a power supply.

    ...The load hasn't been changed, however if it's sagging then that might explain a noise/modulation problem I just heard about on another unit. I just changed the 100AH battery manufacturer because it wasn't lasting more than 18 months -- meaning too high a trickle (float) voltage, or just bad...
  14. drpappy

    Current limiting the output of a power supply.

    --What approach should I take to limiting current?-- I have a constant voltage power supply into a DC converter and a load. There is also a backup battery being trickle charged. My trouble is that traces and components are burning and the 15A fuses are too slow. --RF load...

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