Your vehicle's contribution to your antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KL7AJ, Jun 3, 2010.

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  1. W8JI

    W8JI Ham Member QRZ Page

    It's interesting the little pet peeves we get into, and how we try to set the world straight. The arguments and editorials about "dipole" and "doublet" are one example, and admonishments about the use of "antenna tuner" verses "matching network" are another.

    In the case of counterpoise, someone has looked at textbooks and not found a word used. It appears they have decided we should never use that word.

    The problem is, I get out my copy of the Communications Standard Dictionary and the word "counterpoise" appears. It is defined as "A conductor or system of conductors used as a substitute for earth or ground in an antenna system. Also see; earth, ground."

    As late as the late 80's it was a recognized for what it is commonly used as in our jargon.

    So now that we it appears we have, based on an editorial or two, dispatched a word that Termin, Kraus, Jordan and Balmain, Jasik, Shrader, and that others including RCA and even Hams have used for 100 years or so....what do use to replace it??

    It isn't a radial if it isn't radial, so what do we call this banned counterpoise thing that used to paint a picture in our minds, now that a few people have forever banned the use of the term? A search for "antenna counterpoise" shows 140,000 hits, the limit of my search engine. A few are from a person describing the term as "misused", which might be true, but most are from actual use of the term.

    Say I install a longwire antenna and have a single elevated wire a few feet off the ground below that longwire, and I isolate that system for RF from ground. What do I call that wire used to substitute for earth or a conventional ground? What single word paints the best picture now that we have banned "counterpoise"?

    Say I place an antenna 50 feet in the air, but the earth losses are killing efficiency so I add several parallel wires below the antenna, none of which connect to anything. My ground losses go down substantially, but what do I call the several parallel wires below the antenna that form a substitute for earth? I used to call that a counterpoise system, but now the word is banned.

    I think we have way too much time on our hands, and are looking to create major problems and controversy out of mole hills. With all the misunderstandings around, counterpoise is probably the least misunderstood.
    If we are going to get on a campaign to set the world right and ban the word based on an editorial, at least someone could offer a better commonly used words to replace it.

    Oh, and by the way....try to model a 5 foot diameter single conductor cylinder and mount an antenna on it to emulate your vehicle. It can't be done in any of the common programs. We have to use a grid of cross connected conductors that make up the basic outline of the vehicle to be successful.

    A single small conductor is NOT the equivalent of a complex shape vehicle, it's easy to see that in the real world and in a model. We might get lucky on one or two bands in a few cases, but for the most part it does not work. We need a grid of conductors to build the equivalent of a sheet or a vehicle.

    73 Tom
     
  2. W8JI

    W8JI Ham Member QRZ Page

    This is why the ground or negative return should NEVER be run to the battery post, and recommendations to do that are now being increasingly withdrawn.

    The ground for very high current loads has to go to the block, unless the other end of the negative is fully floated from the chassis and any return path.

    For modest currents, say up to 30-40 amperes, the ground should go to the vehicle chassis near the battery to chassis jumper, but not on that jumper. Sometimes other chassis points are OK, but never to the battery negative.

    Low current stuff like lights can go to the chassis almost anywhere.

    73 Tom
     
  3. AI3V

    AI3V Ham Member QRZ Page

    Yes and no,

    You have to account for any so called "ground loops" when making such a connection.

    Fact is you will have a factory installed wire, heavy enough to handle the entire alternator current between the engine and battery negative,for ordinary battery charging

    Now is a good time to remind folks that the battery is only used to START the engine, once running, the alternator takes over, and the battery may be removed.

    Depending on where the manufacturer picks to sense battery voltage to feed back to the alternator, and where you make your connections, and the current being drawn by both your radio and the car, and wether or not you are operating with the engine running- alternator power, or with the engine off-battery power, will determine if a battery connection is right or not.

    Every case will be different, and needs to be analized.

    Rege
     
  4. K7JEM

    K7JEM Ham Member QRZ Page

    Most newer cars will not continue to run if you remove the battery. Try it on your car and see. Most GM vehicles, as well as others, will die within a second of having the battery removed.
    Most medium power equipment used in a mobile environment will have a single power lead running to the battery, or a nearby factory distribution panel. They will also obtain a ground from a nearby chassis bolt, or installed screw into the car frame or chassis. It's been this way for decades. No one should ever have to run a ground lead back to the battery for loads less than 40 amps or even more.

    Since most radio equipment has its frame at ground, and that frame is usually bolted to the car frame through a mounting bracket, most radios will function quite well without even attaching the ground lead, assuming the bracket is attached to the car with screws or bolts. It is always a good idea to attach the ground wire close to the mounting bracket anyways.

    Joe
     
  5. VK6ZGO

    VK6ZGO Ham Member QRZ Page

    Tom, I've got another one:-

    One of my pet peeves is the use of the term "Dummy Load"

    It is a "Test Load" or a "Dummy Antenna".

    The Transmitter sees it as a real load!

    Realistically, I have no chance of persuading people to stop using the term!:D

    73, VK6ZGO
     
  6. W8JI

    W8JI Ham Member QRZ Page

    I just modeled a short whip on my truck.

    Using the truck wire outline model with dozens of wires, the antenna had 7.2 -j535 ohms. This is very similar to what the antenna actually measures on the truck, within 10-15 %.

    Using the best single wires I could find within the limits of the corner distances and shorter, the model was at closest 40 -j300 ohms

    The patterns were only vaguely similar at best.
     
  7. AI3V

    AI3V Ham Member QRZ Page

    I'll take your word on the late model GM cars and removing the battery, I have a Ford!:D

    But on the second point about where to "ground", Boss has a BMW X5, battery is in the rear, under the spare tire.

    Where would you connect the ground lead for a 100W HF rig mounted in the back? Like I said, every car is different.

    Rege
     
  8. KD0CAC

    KD0CAC Ham Member QRZ Page

    Don't disconnect the battery , all [ haven't tried every car out ] cars with alternators will full-field the Alt. and in short order will burn up the Alt.
    I have been in the auto repair bis. for over 30 yrs. and this has been the rule , there can always be exceptions , but this rule is at least 98+% .
    Since following the rule , I have not on purpose disconnected every car I have worked on , but on occasion disconnect the battery [ an easy way to full-field the Alt. for testing ] , and every car since has run with battery disconnected .
    On my mobile service trucks , I have used only the positive leads to run cranes & plug-in jump-start cables , but prefer to use the extra cable for negative for many reasons , failed connections and " Murphy's Law " .
    The number one problem with electrical in auto's , and especially with computer's in cars is grounds .
    2 of the biggest issues with grounds in computerized cars , is if you lose ground to a device the computer is connected to , the computer will find a ground , and more often than not , the ground it finds , will kill the computer , so finding out what killed the computer is important to keep from killing the replacement .
    Next , what kills the computer in autos , aside from bad grounds , is anything with a coil , like a relay , if the relay fails , like shorting out to ground , that also can kill the computer .
    This all helps to keep " Murphy " from going for a ride .
     
  9. W8JI

    W8JI Ham Member QRZ Page

    I know what you mean!

    http://www.w8ji.com/battery_and_charging_system.htm
     
  10. WA4OTD

    WA4OTD Ham Member QRZ Page

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