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2 Hot Competition Antenna Setup

Discussion in 'CB Antennas' started by dx77HML, Sep 24, 2005.

  1. dx77HML

    dx77HML Member

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    I'm working on a 2 hot antenna system.2 antenna's on top of suburban is exactly 6' apart.Coax used between the 2 antenn's is exactly 6' also.Tried different length's from rear antenna to amp.Low as i got it one time was around 2.3:1 And i'm using an MFJ-259B Analyzer to check.Coax used is LMR400 hardline....Up for suggestion's or idea's as i'm about to give up :roll:

    Thank's

    Danny

    One other thing,i was tuning 2 Monkey Made Fighting Stick's.Also tried 2 MM4 coil antenna's.


     

  2. highroller

    highroller Guest

    Hey 77 I haven't played around with two hot's myself but I know a few guys that have, they seem a little tempermental to get working real well. Have you thought about trying the 1 one with the dead back door I think this will end up working just as well maybe even better. I will try to find some info out for ya on the 2 hot set up.
     
  3. dx77HML

    dx77HML Member

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    Highroller,thank's for your reply.However,i scrapped the 2 hot system.Too many variables in that system.I changed to the bounce back.Rear antenna grounded,front antenna hot.Tuned in a 5 antenna system in less than 2 1/5 hours.Ended up with an swr of 1.0:1 at 50 ohms.Cant get any better.The back door is shut off pretty good too.I went around it with the digital field strength meter and i like the gain.Hopefully it will be very competitive.But,on a sad note,dern transmission went out in my Suburban last night.That thing is turning into a money pit,lol....
    Oh well,gotta spend it on something...hehehe

    Danny
     
  4. AMPOWER

    AMPOWER BANNED

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    what is the velocity of the lmr400 coax??

    I use RG217u coax 66% veloicty factor....
    its 12' from amp to back antenna...
    6' from back to front antenna...
    and 12' of same coax from radio to input of amp...

    Then...you have to tune the FRONT ant 1st...and get is 1.1
    x=0
    Then put that antenna in the rear...and put the front on with the other antenna and retune again....
    My readings with the 259B is 1.0 x=0 50 ohms...

    I think you are using the wrong coax...
    But you are using the correct spacing...

    Have you tried grounding the bottom of both mounts to frame?
    thats annother idea...:)

    Oh yea...put the mfj 259b on the coax going to the back antenna only....

    Hope that helps some...??

    AM POWER
     
  5. dx77HML

    dx77HML Member

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    Thank's for your info Adam.I'm not sure of the velocity factor of the LMR400.Several thing's that you mentioned i did not try.Or did not try in that order.I did have both mount's grounded to the frame though.I agree,maybe it's the coax cable as i changed that on the system i'm running now from LMR400 to RG/213mil.Maybe i'll give it another go another time,but for now i'm gonna leave it as it is seeing as how we have a key down event coming up the 29th of Oct.And now i have the Suburban in the shop getting a new transmission put in it i wont have the time to change it back.But i took note of your reply and will attempt it again.And i'll be sure to let you know the result's.Again thank's!!!

    Danny
     
  6. freecell

    freecell BANNED

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  7. Demon31

    Demon31 Member

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    Adam....Why would he put the MFJ 259b on the coax going to the back antenna?...On a front ant. hot, back antenna grounded there should be NO coax going to the back antenna..
    Maybe I am missing something here...Me or you one is confused here...
     
  8. pinejuice

    pinejuice Member

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    he is trying the 2 hotsetup is thier any dfference in the two and why is in a keydown they dont use this setup 2 hots..
    i dont think you can use lmr 400 try 213 coax
     
  9. mopar2ya

    mopar2ya Member

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    You could use LMR400, you would just have to adjust the length of the coax between the antennas to compensate for the different velocity factors of the coax. The electrical length of 6' of RG213 is 9.09'. To get this same electrical length with LMR400 you would need to use approximately 7.73' of LMR400 to get the same phase difference between the antennas.
     
  10. highroller

    highroller Guest

    I have heard the 2 hot system when next to another mobile that's putting out several thousand plus watts can have reflect problems leading to blown amps. Just something I was told.
     
  11. pinejuice

    pinejuice Member

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    whats the equasion of that lenght ?
     
  12. mopar2ya

    mopar2ya Member

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  13. CRAZY COUNTRY NINE-11

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    My dad (HellRaiser-NYC) told me you can use anything from chain to anchor a Ocean Liner to a fake gold NeckLace....... IF YOU DO NOT KNOW HOW TO USE THE MFJ-IT WILL NEVER WORK !
    OH YEA........! FOR 2 HOTTs:
    1. YOU MUST ABSOLUTLEY HAVE 50.OHMS.
    2. 2ND PERSON AT LEAST 2 MILES,WITH A "TIGHT" METER.
    3. TAKE READINGS "BEFORE" YOU DRILL
    4. THIS WILL TAKE 2 to 6 DAYS.
    I watched him tune 3 suburbans with that 6 foot spacing,they all sounded good.
    the tight meter favored only 1 truck(GMC) the 2 chevy's had to be done over. thank god there was no drilling at this point.
    the spacing on the chevy was longer than 6 foot and the second chevy was longer than that.
    WE CAME TO THE CONCLUSTION THAT GENERAL MOTORS MUST HAVE MADE SOME CHANGES TO THE METAL FOR 1994-95. THE CHEVYs (MINE AND MY BROTHERS) WAS SETTING OFF CAR ALARMS ALL DAY AND NIGHT.
    BUT THAT GREEN GMC(DADs TRUCK) HE CAN KEY UP AND NOT EVEN SPLASH THE NEXT CHANNEL.

    Guys , knowing the velocity factor is a must but not as important as KNOWING "HOW" TO USE THE MFJ!!!!
    YOU CAN USE RG8X FROM THE RADIO TO THE DRIVER,
    RG213 FROM THE DRIVER TO YOUR BIG BOX AND RG217 FROM THE BOX TO THE FIRST ANTENNA AND 9913 TO THE SECOND.

    YOU CAN USE CHICKEN WIRE!! IF IT's THICK ENOUGH TO HANDLE THE "HEAT" AND "50-OHMS"
    EXAMPLE:
    1. 102 INCH STEEL WHIP AND 9 FEET OF RADIO SHACK THICK COAX IS 50-OHMS
    2. 102 INCH STEEL WHIP AND 9 FEET OF RG217 IS LESS THAN 50-OHMS
    3. 102 INCH STEEL WHIP AND 9 FEET OF LMR600 IS NOT 50- OHMS
    4. OUT THERE IN THE CB WORLD(SAYING NO NAMES) THERE IS A GHOST RIDER BOX .................
    DRIVEN BY VARIOUS DRIVERS THAT HAS TRANSISTORS.
    THE GUY KEEPS BLOWING HIS DRIVER. MY DAD BET ME $500 DOLLARS THAT SYSTEM IS NOT 50-OHMS "OR" CAN NOT HANDLE HEAT!
     
    Shadetree Mechanic likes this.
  14. jon666

    jon666 Sr. Member

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    the godfather of amps has spoken rofl
     
    Captain Kilowatt likes this.
  15. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Yup. Been here for two and a half years and finally spoke up. :ROFLMAO:
     

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