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Trouble with SWR with Magnum 257! Please HELP!

Discussion in 'General CB Services Discussion' started by hacksaw, Feb 1, 2009.

  1. hacksaw

    hacksaw Active Member

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    Hi, I bought a brand new Magnum 257 blue light radio and a brand new Wilson 1000 trunk lip mount antenna to install in my Honda. I ran the power wires dirrectly to the batt. I attached a #10 copper jumper dirrectly to one of the set screws on the antenna and back to the body of the car. So, grounds are not a problem. I noticed that the 257 had extreeme engine noise, and static. So when I started to set the antenna, I could not get the swr below 1.7:1 when the engine was not running. I noticed that when the engine is running, the meter shows over 1.1:1 without keying the mic, and if I key the mic, swr shoots to over 2.1:1. I tried a different radio, a RCI 2950. Perfect results. Very quiet. Zero engine noise. 1.2:1 swr across the band. What is the deal??? Any input on the 257? It is currently back in the box!

    Shawn


    #1
  2. Robb

    Robb Yup

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    Wiggle any of the coax wire to see if it changed the SWR at all? Are you certain that the ground strap on the antenna is a solid as you think?
    Did you try to see if re-adjusting the antenna itself for the 257 made a difference? One would think that it should be the same, but you don't to assume anything right now - right? I understand that the 257 has been known for being a bit noisier; but the SWR has never been mentioned in anything that I've read about it. I would check the ground points on everything again and try to find a fault there.
    Just two cents worth.
    #2
  3. hacksaw

    hacksaw Active Member

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    Hey, thanks for the reply. Yes, I have made sure that my antenna ground points are solid connections. The accual trunk lid is skin is glued to the inner supports, and there are plastic washers on the hinges that attach the deck lid. That is why I took a grinder and cleaned the paint and glue off of the lip, then ground the paint off of the body of the car under the rear pannel, where the deck speakers are, and bolted a # 10 copper strap with crimp ring terminals from the antenna set screw and the body. I wired both the 257 and the 2950 harnesses to the same cables that run dirrectly to the batt + and -. I tried both radios several times today. Checking swr, along the way. With the engine running and not. I am 110% positive that there is nothing wrong with any coax, antenna, coax jumper, swr meter, or any ground that I have installed. I am a Powerlinman by trade and tend to go over board on wiring, because I have access to all sorts of very high end connectors, oxygen free copper, etc.... So, I believe that the noise in the 257 has something to do with the swr reading. Either the meter is getting feedback from the radio somehow, I do not know. All I know is, you can set the swr meter and with the car not running, it reads nothing, as it should when you are not on tx. BUT>>>> when you start the car while watching the meter, it moves upward and also moves up as you rev the engine. Like I said, I think it is something going on with the noise????? Thanks for your input, hopefully someone will help me figure this out. Sucks to be talking on a used radio while your 2 day old, radio is boxed up. Thanks

    Shawn
    #3
  4. Beetle

    Beetle Well-Known Member

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    You ARE using an external meter, right? The built-in meter in most radios is barely good enough for relative indications. Don't rely on them for anything but that.
    #4
  5. hotrod

    hotrod Well-Known Member

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    on the 257 make sue the nb/anl are on and set the tone to low
    trunk lids have very little to no ground at all. i highly doubt that 1 single
    ground strap is gonna do much good.make sure when ya check swrs
    i like to turn dk down all the way and mic down all the way if ya have any type
    of noise when doing swrs your needle will move up with the noise.personally
    a roofmount is the best way to go as far as grounding.magnet on the roof works
    great also.being on trunk its most likely picking up your fuel pump.the magnums
    ive owned over the years have always had better recieve than a 2950 probaly
    why its picking up noise in the first place.just what ive found to be true with equiment
    ive have owned and used
    #5
  6. packrat

    packrat Active Member

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    257

    Sounds to me like your meter is picking up rf from your ecm when the engine is running, and acting like a tach. Just something to look for.
    #6
  7. packrat

    packrat Active Member

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    You might try running a ground fron the antenna ground point on the body and antenna mount directly to the neg. terminal on the body near the battery.
    #7
  8. freecell

    freecell BANNED

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    "I noticed that when the engine is running, the meter shows over 1.1:1 without keying the mic...."

    if the transmitter isn't energized you're not measuring vswr.
    #8
  9. hacksaw

    hacksaw Active Member

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    Ok, here is what I have done today. I ran a larger copper wire #8 awg from the batt pos. and neg. and ran it across the front of the car, and down the driver side fender into the fire wall. Before the wires were #10 and ran dirrectly from the batt and across the under hood fuse box, and lots of wire harnesses on the pass. side and into the fire wall. I made up a new #4, fine stranded copper jumper and replaced the old # 4 factory jumper from the engine to the body by the engine mount. I have double checked everything on the car itself. All grounds are good. Now, for the antenna. I have ran mag. mount antennas before. With good luck I might add. However, I am unclear on how they can ground better than a trunk lip mount. The trunk lip antenna is grounded very well. Should it not be grounded? On these Hondas, the out skin on the deck lid is attached to the inner supports with glue. And the hinges use plastic washers. So, I figured that my best be would be to attach a ground to the antenna mount base where the set screws attach it to the lip, and back to the body of the car. I used a grinder and lightly buffed the paint off of both the inside of the lip, and the body of the car under the trunk where the deck speakers are. I think I noticed a slight change in noise level going down by either running the power wire to the opposite side of the engine comp., or by changing the ground strap on the engine. In either case, the 257 still has much more noise than the 2950.

    Now, for the swr. Some of you I think were un-clear on what was going on. Me to, that is whay I asked????? Yes, I use a simple, in line swr meter. I tired a jumper that I had made, I think about 18" long, and one that I bought new. Both same results. No problems with the 2950 at all. But with the 257, that is where it gets funny. If the car is not running, I can cal. the swr meter just fine. When I key up on low power, it still reads higher than the 2950 does. BUT, if I start the engine, when the noise level get high in the radio, the meter will not come back down all the way. If I cal. the swr at that point, the needle moves arround, and stays about 1.3:1 without keying. And yes, the radio is powered up. So it is picking up something other than swr right. But, it DOES NOT DO THIS WITH THE 2950! I am out of ideas!!!!

    Thanks

    Shawn
    #9
  10. Robb

    Robb Yup

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    SWR can only be see on the radios SWR meer IF the mic is keyed. You're not making sense at this point. How can you see the SWR if you aren't keying the mic? If you are seeing meter movement without keying the mic; then you have to be seeing recieve info.
    Please clarify?
    #10
  11. hacksaw

    hacksaw Active Member

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    Ok, sorry. I thought I made it clear. I AM NOT using the swr meter built into the radio. The 257 does not have a built in swr meter. I am using a simple swr/field strength meter. I have run the antenna lead into the ant. side of the meter, and a 18" coax jumper into the transmitter side of the meter. AND YES, when you start the engine, with the radio on, AND NOT KEYING THE MIC UP, you can watch the needle move off of the rest and up to about a reading of 1.3:1 on the meter. It does not matter if you caliberate the meter, it still kind of flutters as the engine is running. Now, if you turn the engine off, you are able to cal. the swr meter, and get a reading. Which is higher on the 257 than the 2950 I might add. At this point I am trusting the reading with the 2950 which I was able to cut off about 3/8" off the whip and get the swr to a flat 1.2:1 on channel 1 and 40. If this is still confusing, well, I am sorry, I am completely lost on this one to. I might add, any electrical device in the car that could put off noise is picked up on the 257 and not the 2950. Door beeper when keys are left in, elect. fans kicking on, turn signals, elect windows, wipers, door locks, etc... You can hear it on the 257. I was told that the Magnum uses a common chassis ground where as the RCI uses a floating chassis ground. Could this be anything as to why I get the noise?????????????? And funkie swr meter readings with the 257??????
    #11
  12. Robb

    Robb Yup

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    OK; how about this...
    First point: The Mag257 has a noisy recieve; there is nothing wrong if you are hearing noise with that radio. Regardless if it noisey or more noisey with the engine running or not - it is a 'non-issue. The Mag 257 is known and documented as picking up a lot of noise - probably the worst thing about that particular radio. That is not an issue - forgettabouttit. Ignore the noise issue - it has nothing to do with the funky meter or your SWR. To deal with the noise issue; you will need to put a filter inline between the radio and the battery. That is how that is handled.

    Second point: If the inline SWR meter is moving while recieving - it has nothing to do with the SWR. The 'SWR' is only a ratio of the radio power being reflected back into the radio WHEN keyed down. It cannot read SWR UNLESS there is power LEAVING the radio. NOT recieving on the radio.

    Third point: Chances are, that the antenna will need to have the SWR set to each radio separately.
    Either that, or just run the 2950 in the vehicle and forgetabout the Mag257. You've already cut the antenna to adjust it to the 2950; so why not run with it? If you re-adjust the antenna to the Mag257; then it probably won't be right for the 2950.

    Am I getting this right? Am I missing something here?
    I hope this helps
    Last edited: Feb 2, 2009
    #12
  13. hacksaw

    hacksaw Active Member

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    Thanks Rob, I think I will run the 257 in the house for now. Probably wont be near as noisy on a regulated power supply. Unless it picks up fan noise??? I have never had luck with inline filters. Have you? Anyhow, your right. Probably need to run the 2950 in the Honda since I set the swr for that radio set up. And it is low and very broad. Seems to work great. I guess I was a little dissapointed with having bought a brand new radio and having that trouble right from the get go. I once had a Magnum delt force. RF limited sent me a rx kit to install because it had terrable noise. It helped some, but not enough for me to keep it. You guys are great. Glad to be a part of the forum. I will consider this question answered. Thanks

    Shawn

    PS: I havent tried the radio inside yet cuz my tower is currently apart for maintance. I will be working to get it back together soon. Have to build a new center section for 20 feet taller. thanks again
    #13
  14. packrat

    packrat Active Member

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    257

    Another variable is the power output of the radio. The higher the output, the higher the swr, to a point. You would need to readjust as was stated earlier. I have a 257 and do not have any of these issues with it. As you were told earlier, you need to take each radio on a case by case basis.
    #14
  15. W5LZ

    W5LZ Crotchety Old Bastard

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    From what you've described, the 'problem' seems to be with that particular radio. No idea why, but what else is changing? When you do find that problem it's probably going to be something fairly 'simple', sort of. Maybe. Good luck.
    - 'Doc
    #15


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