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Discussion in 'General CB Services Discussion' started by hacksaw, Feb 1, 2009.
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.
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.
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
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.
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.
if the transmitter isn't energized you're not measuring vswr.
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!!!!
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
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
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.