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Using a Common Ground?
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What are you trying to hook up? If you run a heavy cable from the battery to the distribution block, you *can* get a lower net resistance than running a bunch of smaller wires from the battery to a bunch of loads, plus the wiring is a lot easier to deal with. The most common problems with grounds are either a bad connection or the voltage of the local ground connection gets raised by a fault or heavy load (as an analogy, think of what happens when you are draining the kitchen sink when your dishwasher hits the end of the wash cycle and starts draining into the same pipe).
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John
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John
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My Yaesu FT-8800. The main issue I'm worrying about is the (electrical) interference you can get if you don't run a dedicated power wire for the HAM rig that is separate/isolated from power that is being supplied to other things. Can the same thing (interference) happen if you don't (also) isolate the ground wire?
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Yes, it can. On the other hand, I have the radio in my truck hooked into the distribution block in the cab on the positive side without a filter, and the return tied to chassis in the cab at one of the ground terminals without any difficulty. But, it's a diesel, so there isn't any concern from RFI from the ignition system, and the injection system is fairly low frequency. If it's easy to get the ground wire to the battery, I'd just hook it up there (it sounds like you've already got a path for the positive lead). If it's difficult, I'd try connecting to the chassis in someplace convenient, and see if you either get noise in your transmitter output or your car has operational difficulties when you transmit. Of course, there is the remote possibility that you could fry something in the course of finding out that you have a problem...
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John
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John
Generally speaking, it is better to run the power wires for a radio, both the positive and negative, directly to the battery. However, it is not necessary nor will that eliminate any rfi (radiated frequency interence). In fact we have found that both the Terratrip and the AlphaPro emit interference on specific frequencies causing us to change our comm frequencies.
Also, with a DC system, there is technically no such thing as an isolated ground. And with AC systems, there is rarely ever a need for an isolated ground as defined by the electrical code. An isolated ground receptacle for a computer, or a point of sale system can do 3 things, 2 of which are bad.
Richard the electrical engineer
Also, with a DC system, there is technically no such thing as an isolated ground. And with AC systems, there is rarely ever a need for an isolated ground as defined by the electrical code. An isolated ground receptacle for a computer, or a point of sale system can do 3 things, 2 of which are bad.
Richard the electrical engineer
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Richard,
I don't agree with that... in some very specific instances, it can. Mostly if there is already a large noise current in the "ground" that you are connecting to and whatever you are connecting has a conducted susceptibility to that frequency.
Matt,
What kind of filter do you have?
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John
John, rfi comes in on the antenna, not on the power leads. I can't think of any thing you can do to the power that will clean up the signal on the antenna. And that includes running off of internal batteries such as with an HT. The Terratrip causes noise even on those if they are close.
Also, as defined on the power systems I work with, there is no 'ground' in an automotive DC power system. In AC systems, the 'ground' is a redundent return path for current in case of a short. The 'neutral' is the normal return path. In automotive systems, the ground is simply the normal return path for current from the positive side of the battery to the negative.
Also, as defined on the power systems I work with, there is no 'ground' in an automotive DC power system. In AC systems, the 'ground' is a redundent return path for current in case of a short. The 'neutral' is the normal return path. In automotive systems, the ground is simply the normal return path for current from the positive side of the battery to the negative.
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I don't agree with that either... granted the ambiguity of the term is probably why it doesn't appear in MIL-STD-464. I do agree that if you have a radiated susceptibility (either through an antenna or some other path) that you aren't going to fix it with the power leads. But, lots of bad stuff that is really on the power line either coming into or going out of a device gets blamed on antennas, bad shielding, and "radiated noise". I can even cite a specific example of a PWM stepper motor drive and an ultrasound system (granted, in that case it was both a conducted and radiated susceptibility). Since antennas and receivers are tuned devices, in my experience they are usually the smallest problem, unless you are trying to pick a signal off something that is flying in front of the Sun. I do also agree that "ground" is a confusing term when it comes to anything that isn't actually electrically tied to the earth, so I tend to use "chassis" and "return" when it's important. Who says we don't ever talk about interesting technical topics on SS anymore?
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John
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For a filter I'm using the Powerwerx DC line noise filter (http://www.powerwerx.com/adapter-cables/dc-line-noise-filter-oem-t.html). Even with the filter and running both leads to the battery, at NEFR I (also) had some RFI from the Terratrip depending on what radio frequency I was on (somewhere in the 146 range). I didn't have that problem at STPR or Black River (some of the frequencies were close, but not exactly the same). At this point I'll just plan to also run everything straight to the battery.
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Huh... The good news is that it looks like your filter should be taking care of anything that is coming in on the power line, so it probably really doesn't matter how you route it back to the battery except from a voltage drop perspective. Is the noise a problem when you are receiving, transmitting, or both? Also, are you sure it's the Terratrip? How close are the wires between the filter and the radio to the Terratrip, and how close is the radio to the Terratrip? Google found some complaints on another forum about interference with a CB, so I really doubt it's something coming from the antenna, though the fact that it's frequency dependent gives it some credence. But, that'd be hard to do even intentionally. One other thing you could try is putting the filter on the Terratrip. Is the cable to the pickup two wires or just one? If it's one, that probably won't work.For a filter I'm using the Powerwerx DC line noise filter (http://www.powerwerx.com/adapter-cables/dc-line-noise-filter-oem-t.html). Even with the filter and running both leads to the battery, at NEFR I (also) had some RFI from the Terratrip depending on what radio frequency I was on (somewhere in the 146 range). I didn't have that problem at STPR or Black River (some of the frequencies were close, but not exactly the same). At this point I'll just plan to also run everything straight to the battery.
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John
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The noise is constant (when sending, receiving, or just listening), and I know for sure it's the Terratrip causing it because when I turn it off (and back on) the noise stops (and starts). The filter is plugged into the factory cord for the radio, so there's about 6 inches of wire between the two (and about half of that is taken up by a fuse). The Terratrip is mounted above the glove compartment and the radio is mounted on the back of the center console/arm rest (between the front seats). Even though they both use separate power wires, the wires enter the cabin in the same bundle, though they split before the filter for the radio.
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Since I don't have a Terratrip, forgive the stupid questions, but (1) is the case plastic? (2) is there any part of the case that is metal that is electrically tied to the battery return wire? [can check with an ohmmeter] (3) can you disconnect the sender from the unit? [I am assuming that you have a wheel sensor] (4) do you have any other wires running out of the Terratrip, such as a reset switch? If the answer to (1), (2), and (3) are yes, and the answer to (4) is no or that you can either disconnect or bring all the switches close to the unit, the first thing I would do is disconnect them one by one and see if the problem goes away. If it doesn't (don't laugh...), I'd get some heavy duty tinfoil and wrap the Terratrip in it, making sure that it's completely covered and that that the tinfoil is tied to the metallic part of the chassis. If that makes it go away, this might be a difficult problem to solve.
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John
1) The case is plastic. 2) I assume somewhere inside there is a connection to the negative lead from the battery but none of the case is metal. 3) a little difficult as power, reset, pickup units, etc all go through the same plug on the back of the Terratrip 4) That would isolate which one of the wires, if any, is acting as an antenna. That wire could then be changed to a shielded cable. And tin foil might work. However, the problem is so frequency specific that simply using another frequency still in the 2 meter band works.
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Just some food for thought from someone with a bit of experience in electrical do-dads:
DC batteries actually have a flow of electrons from "neg" to "positive". So your noise may very we'll be coming from your ground (chassis) and that is why running a direct neg to a battery can help. You could try filtering the ground as we'll.
Avoid running high amperage or high gain wires (like your antenna) parallel to any power lines to the radio. Cross at right angles as this will reduce or eliminate the induction of unwanted frequencies.
Shielded cables can be (and often are) terminated incorrectly. Ground ONLY one end of the shielded cable. This protects unwanted freq from induction into the cables inside. By grounding both ends you build a mini transformer.
If all else fails, find a scope and hook it up to your power supply to the radio, you can find all sorts of interesting things traveling threw the cars power lines.
Have fun
DC batteries actually have a flow of electrons from "neg" to "positive". So your noise may very we'll be coming from your ground (chassis) and that is why running a direct neg to a battery can help. You could try filtering the ground as we'll.
Avoid running high amperage or high gain wires (like your antenna) parallel to any power lines to the radio. Cross at right angles as this will reduce or eliminate the induction of unwanted frequencies.
Shielded cables can be (and often are) terminated incorrectly. Ground ONLY one end of the shielded cable. This protects unwanted freq from induction into the cables inside. By grounding both ends you build a mini transformer.
If all else fails, find a scope and hook it up to your power supply to the radio, you can find all sorts of interesting things traveling threw the cars power lines.
Have fun
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