What are the best and worst vehicles to run power in?

[dudmuck]

Also, there is no DC component on the coax, because dc is decoupled from rf in the transmitter and the amp. So, if there is no current flowing on the braid, how can it function as part of a ground loop? It can't.

The center conductor of the coax is DC blocked, but not the shield.

On every radio I know about, the shield of the antenna connector is mounted on the chassis, and the chassis is connected to (-). So if the other side of the coax screws onto an antenna connector which is mounted on the vehicle chassis, then (-) DC current can flow thru this coax shield. If you disconnected the (-) black wire on the radio, and insulated the radio chassis from vehicle chassis, then all the radio's DC current would flow thru the coax shield. So to prevent ground loop, the (-) wire on the radio needs to be sized sufficiently so that current only flows thru that (-) and not the coax shield, or any other part of the vehicle chassis.

 

[unit_399]

Hey DUD -

You're right about the antenna braid becoming a dc conductor IF the negative power lead opens up, but I don't think that's the problem with LC's setup. I don't fully disagree with Freecell about ground loops being the problem. The only thing I disagreed with was his drawing, which, if it wasn't wrong, was at least misleading.

LC -

Forget about what I said about grounding the radio and the amp...it ain't gonna help. I did a lot of looking on the net, and I found a lot of info on ground loops, but most dealt with audio system installs. But this one http://www.k0bg.com dealt specifically with mobile HF radio installations. Scroll down to GROUND LOOPS. maybe you'll find some help there.

- 399

 

[Switch Kit]

I love this ......If you're using a mag mount antenna, and you have whine on your transmitted signal, try this. Replace the antenna with a dummy load. If you can still hear the whine on a near-by receiver, the problem is in the DC wiring, or the alternator (albeit doubtful). If you can no longer hear the whine, then ditch the mag mount and drill the necessary hole.

 

[W5LZ]

Without getting into a big deal about it, ground loops are almost always possible. There does not have to be a direct connection to produce them, that connection can also be inductive or capacitive. While eliminating those loops is the best way of 'curing' that problem it isn't the only 'cure'. Reducing the results of those loops to a point where they are not noticeable also works 'good enough'. If you have a choice, do away with the loop. If it's not possible, then compromise and reduce it to a usable level.

The above is the main purpose of this post. The rest is just for something to think about.

What's the 'beef' with the ARRL's compilation of 'experience' dealing with radio stuff? You might not be thrilled with the ARRL as an organization (me either, even as a member), but they do provide information that has been 'tested' over quite a long period of time. That information has been challenged and in almost all cases, the 'corrected'/revised information presented. (R. Measures and amplifiers is a very good example of that 'challenging' thingy.) Don't wanna take the advice of people who have already done that testing? Hey, that's fine, do your own testing, nothing wrong with that. Just remember, those 'wheels' have been around for a very long time, re-inventing them doesn't do much except provide fun for the "re-inventor".
Have fun...
- 'Doc

PS - The ARRL used to be very, very good at what they did. From experience, I've found that their later endeavors aren't exactly the 'best' in my opinion. Then again, I'm prejudiced cuz I might have fell through one of those "holes" you hear about. Their saying that it would end up in such a particular way was correct. They didn't provide any help in my particular case, but the result did come out as they said. It sure didn't say much about all the trouble I had to go through though!
The latest 'dumb' thing I've seen them do is offer me a special life membership. At current prices, I could pay the yearly rate and it'd be cheaper! I very much doubt if I'll live long enough to make that life membership profitable to me. But, that's "bid-nez" not RF...

 

[mackmobile43]

"Also I have my body grounded to the frame in 2 places and have no problems." I do not how ever have my equipment double grounded."

we're not discussing body to frame bonding here.

"I do not how ever have my equipment double grounded."

if you have a transceiver and an amplifier connected to central point ground and a piece of feedline connected between them you have multiple ground paths, period.

"eliminate any and all instances where MORE THAN ONE GROUND CONNECTION PATH exists...."

eliminate any and all instances where MORE THAN ONE GROUND CONNECTION PATH exists BETWEEN ANY TWO PIECES of equipment.

Are you saying that each piece of equipment in that typical station setup should have it's own lead to ground and it's own ground rod into earth?
if so you've single handedly wiped out the buss bar market.lol

The only way that setup pictured would fail to send each piece of equipments path of dc to earth is if the buss bar failed and one and that piece of equipments path to ground depended on the shielding of the coax to the next piece of equipments path to earth or in the case of a dc powered units path back to the battery.

For those who are'nt quite comprehending the jist of my ramblings, always run the ground wire of each piece of equipment to a direct path to ground or connect directly to the - side of the battery and that's all you can do and if that path is interrupted then that's what troubleshooting is all about.

 

[Switch Kit]

IM all looped out You know what this tends to remind me of Doc ?
Like whats the best length of coax to the antenna. Even looks like Mac's trying to get a better understanding here ? Like I said LC , you ain't alone dude. If Freecell told us or took the time to spell it out from time to time ? he'd more then likely have to kill us. ( IM kiddding )

I always enjoy reading your posts Doc , thank you.

 

[unit_399]

Dudmuck -
At first glance I agreed with you about dc current flowing through the antenna coax braid if the radio negative battery lead opened up. But after thinking about it a little more, I remembered that rf /earth ground (connected to the chassis of the radio) is separate and is isolated from DC ground. They are capacitively-coupled, but not dc-coupled. I verified this by opening up my 2950, and ,sure enough, the pads for the mounting screws that hold the board to the chassis were not connected to the circuit except through several 470 pf caps. You can easily check this by hooking up an ohmmeter between the negative power lead and the chassis. The only time it will show conductivity is if one of the caps is shorted. Now I don't know if this is the case with amplifiers, but it seems to be true of most radios. My old TRC-458 (circa 1977) was set up the same way. So, it would seem that the antenna system couldn't be a component in a dc ground loop, but Murphy will probably prove that one wrong too. LOL.
- 399

 

[BOOTY MONSTER]

"eliminate any and all instances where MORE THAN ONE GROUND CONNECTION PATH exists...."

eliminate any and all instances where MORE THAN ONE GROUND CONNECTION PATH exists BETWEEN ANY TWO PIECES of equipment.





cant see the forest because all the trees are blocking your view ?

 

[unit_399]

Booty -

I guess the key word in what you're saying is between. It seems that for proper dc grounding and to eliminate loops, that the power leads from each piece of equipment should be connected directly to the battery. That way the only connection between pieces of equipment is the coax. Right??

- 399

 

[loosecannon]

thanks for the input,

i have tried grounding both the amp and the chassis of the radio.
didnt change a thing.
not sure if i ever mentioned grounding the radio, but grounding the amp is in one of the posts im pretty sure.

freecell is not guessing about what he is stating, he just wont lay it all out for me.
maybe he wants me to join the portal.
oh well,
LC

 

[formulamojo]

thanks for the input,

i have tried grounding both the amp and the chassis of the radio.
didnt change a thing.
not sure if i ever mentioned grounding the radio, but grounding the amp is in one of the posts im pretty sure.

freecell is not guessing about what he is stating, he just wont lay it all out for me.
maybe he wants me to join the portal.
oh well,
LC

Pricey answer.

 

[loosecannon]

wow!

i have to say that the longer this thread gets, the more i end up repeating myself, and things are still getting all confused.LOL

i dont mind repeating myself, but im not going to start over again.LOL

FREECELL- exactly what question are you referring to in this statement?

"no, it's absolutely correct and only the elimination of multiple ground paths between equipment will solve the problem. that's 5 times now that i have answered the question."

because i never asked for someone to give me the theoretical principle behind my situation.
i asked for HELP in solving a problem. to that end you have been less helpful than most here.
i am the one who started this thread, and the purpose was to get ideas of what to try from people who know more than me.
well, i agree that you know more than i do about this stuff, but you seem to have no desire to actually help me solve the problem.

why wont you utilize the knowledge and experience you have to apply your principle to my specific installation?
tell me how, in my installation, i should go about eliminating all instances of multiple ground paths between two pieces of equipment.

i will even make it easy for you by repeating the situation once again so you dont have to go reading through all the back posts:

my amplifiers negative power wire is connected to the chassis of the amp directly. (i think most amps are this way)
the negative power wire goes from the amp to the negative terminal of the battery.
the battery has a heavy gauge wire that connects the negative terminal to the vehicles body.
the amp is connected to a low pass filter with coax.
the low pass filter is bolted to the vehicle body.
the low pass filter is connected to the antenna with coax.
the antenna is hard mounted to the roof of the car.

now, can you please tell me specifically what i need to change in this setup to make it work correctly?
because i cant see any way to do what you are suggesting.

Switch Kit- with the amp off, or not in line, the SWR is 1.1 to 1, according to two different SWR meters.
antenna install is fine.
the reason the SWR is 3 to 1 with the amp on is because it is putting out harmonics of the original 27mhz signal. (54mhz, 108mhz, etc...)
the antenna is only designed to be resonant at 27mhz, so those harmonics get reflected right back to the amp causing the high SWR reading.

putting the low pass filter inline after the amp attenuates those harmonics to the point where they are no longer a problem.


Unit399- i have been to that site many times.
very helpful and informative, but i have already tried all his suggestions.

thanks to all for replying,
hey, who knows, maybe it is very simple!
LC

 

[W5LZ]

LC,
I'm not answering for 'freecell', but I think his reply means that the 'cure' is eliminating ground loops. And, that's true, if you can.
The problem is that there are ground loops -possible- if there are more than one connection between any two things. Since it's almost impossible to eliminate all of those multiple connections and still have an operating system, the best you can do is to reduce any unwanted results. That 'reduction' isn't limited to only one route, eliminating the loop entirely. Shielding, isolation, filtering, etc, all help with that. All of those things don't mean being done only to the radio string of equipment. It means also being done to the other stuff around that equipment that -might- be causing part of the problem. Oh @#|+, lots more work, huh? 'Fraid so.
Not having ever been in your particular situation before, I don't have an absolute answer, wish I did (not really, who wants to go through that, right?). The first step is to eliminate what you can. The second step is to reduce power till it isn't bothering whatever is being bothered. Not enough power left to be usable? Go back to step one again. Repeat as necessary.
Will you eventually 'cure' it? Probably. If not, a very large hammer does wonders in making you feel better, the satisfaction in teaching that sorry @#$%$# that you're the boss, you know? That's the last resort, don't get too much in a hurry to use it.
Good luck.
- 'Doc


Five gallon bucket of torroids and ceramic capacitors. They come in very handy.

 

[dudmuck]

i dont mind repeating myself, but im not going to start over again.LOL<snip>

To re-iterate, the original problem was RFI getting into the vehicle electronics.

As far as ground loops go, we are talking DC ground... the best method is to eliminate RF from the picture by using a dummy load instead of an antenna. With this you will still have the same amperage draw from the vehicle, but no radiated RF. If you still have trouble, then its certainly a DC power problem, such as ground loop. But if you only have trouble when transmitting into the antenna, then its purely an RFI problem and not a ground loop. But the only way to be sure is with a non-radiating dummy load.

I think if it is a ground loop problem, then life would be easier.

Obviously you know the first item about RFI is bonding the vehicle chassis with braided straps.
These straps need to be mounted on sanded surfaces, so they're attached to bare metal instead of paint or oxidization. The first place to strap would across the engine hood hinges, then the engine itself, then the exhaust tailpipe. The tailpipe is mounted on plastic & rubber so vibration doesnt cause rattling.

Snap-on ferrites do help, but it often requires many of them to be effective, since they arent a single piece, their effectivness is reduced. It would be helpful to know the signalling method used by your computer, because it should be CAN bus which is differential and that means common mode interference should be reduced. Maybe the vehicle is too early for CAN bus.

399: correct, the 2950/2970 has a separate chassis and RF ground. I think thats possible because it only operates on 12/11/10 meters. HF rigs cant be that way since they operate on much lower frequencies.

 

[freecell]

"we are talking DC ground...."

no we're not.