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Trouble with SWR with Magnum 257! Please HELP!

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Old 01-31-2009, 04:24 PM
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Default Trouble with SWR with Magnum 257! Please HELP!


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


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Old 01-31-2009, 05:36 PM
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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.
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Old 01-31-2009, 06:43 PM
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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

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Old 01-31-2009, 09:58 PM
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Quote:
Originally Posted by hacksaw View Post
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 This does not necessarily constitute "ground" for RF purposes.. 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 How is this possible? If the meter reads upscale with no input, it's defective, or hasn't been zeroed. 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! Some radios are more susceptible to noise than others.

Shawn
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.
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Old 02-01-2009, 06:11 AM
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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
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Old 02-01-2009, 07:11 AM
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Default 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.

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Old 02-01-2009, 07:15 AM
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Default 257

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.

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Old 02-01-2009, 10:18 AM
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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.

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