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New cb
Sept 7, 2018 13:31:00 GMT -5
via mobile
Post by redryder on Sept 7, 2018 13:31:00 GMT -5
Recently bought and installed cb. Basic Cobra model, adjustable Firestick antenna for a “ no ground plane” set up on a Jeep Wrangler, because of the fiberglass top. When complete with installation I checked my SWR’s as follows Chan 1 SWR 1.4, Chan 10, SWR 1.2, Chan 19 SWR 1. Needle barely moved. Same for Chan 30 and Chan 40. My problem is the output sounds a little distorted to other drivers. It’s a little better the farther away I hold the mic.
Just wondering if I need to adjust the antenna to maybe increase the SWR closer to 1.5. Or could it just be the absence of a good ground plane due to the Jeep fiberglass top??
Appreciate your thoughts/advice
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Post by 2600 on Sept 7, 2018 16:04:36 GMT -5
Most, but not all Cobra models have a mike gain, or "Dynamike" control. Sounds as if yours is turned up a bit too high. If turning it down improves the situation, it's a simple fix.
The name "Cobra" is a bit like "Ford". Might be seen on a big OTR tractor, a farm tractor, or a 4-door Focus. Not all Cobra radios are created equal.
Frequently the circuit inside the radio that holds your mike audio below the distortion point will be disabled, for the purpose of making the transmit audio louder. Common name for this is the modulation limiter. Disabling it is frequently called "clipping" the limiter. If you are using a factory-stock mike, you may find that it has to much bass response. This makes it necessary to hold down the level of the mike audio, since those bass tones distort first, and tend to cover up the part of your voice audio that makes it understandable. A typical truck-driver style "noise cancelling" mike usually reduces that bass response, and raises the upper limit on how loud you can crank it before you're hard to understand.
Or you could just get in the habit of holding the mike far enough from your face while transmitting.
73
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New cb
Sept 7, 2018 16:44:09 GMT -5
via mobile
Post by redryder on Sept 7, 2018 16:44:09 GMT -5
Thank you for the info. This particular radio cost about 50$ at Walmart. Very basic, just volumn control and squelch. The mic is simple push to talk, no controls as you mentioned. Years ago, I had a Cobra with all the bells and whistles but rarely used any of it. I mainly bought this so when road traffic came to a stand still, maybe I would be able to take an exit and find a way around the bottle neck. Mainly to just keep up with road conditions, but from time to time be able to ask a question.
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Sandbagger
Administrator/The Boss
Posts: 6,245
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New cb
Sept 7, 2018 17:31:37 GMT -5
Post by Sandbagger on Sept 7, 2018 17:31:37 GMT -5
Thank you for the info. This particular radio cost about 50$ at Walmart. Very basic, just volumn control and squelch. The mic is simple push to talk, no controls as you mentioned. Years ago, I had a Cobra with all the bells and whistles but rarely used any of it. I mainly bought this so when road traffic came to a stand still, maybe I would be able to take an exit and find a way around the bottle neck. Mainly to just keep up with road conditions, but from time to time be able to ask a question. Well, if it's a new, unmodified radio, the transmit audio should be crystal clear (even if a bit low and flat). SWR should not affect audio quality directly. You want the SWR to be a low as possible. Based on your readings, you might want to lengthen the antenna a small amount to better balance the match across all 40 channels. But back to the distorted audio, it is possible that because of the "no ground" nature of the antenna, RF currents could be flowing back down the shield of your coax cable, and getting inside the radio and mucking up either the audio circuit (low level squeal), or the PLL VCO (FM'ing). What you might want to try is making sure the radio itself is firmly grounded to the chassis of the vehicle, or get a couple of clamp-on ferrite blocks and place them on the coax cable near the radio. This problem is more noticeable with cheaper radios (at least that's been my experience). Or it might just be a crappy mic element. Try a different mic on it and see how that works.
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New cb
Sept 7, 2018 22:43:44 GMT -5
Post by 2600 on Sept 7, 2018 22:43:44 GMT -5
They used to print "electret" on the rear of a mike when the factory built the radio that way. If the factory mike has that printed on the rear side, use caution with changing mikes. A dynamic mike may not like having the electret mike's DC-supply voltage feeding into it.
Most aftermarket mikes are meant to use with a radio wired for a low-impedance dynamic mike.
The bottom-dollar three-knob model tends to use the cheaper electret mike. The radio has to supply operating voltage to this mike, but it is piggybacked onto the audio wire, along with your voice audio coming back down the wire to the radio. This is where the hazard to your dynamic mike comes from.
They have really good bass response.
Trouble is, that's a liability for AM CB transmit audio.
It really sounds as if this radio got turned up, returned to WallyWorld, repackaged and resold.
The original factory adjustment for the audio limiter should keep it clean-as-a-whistle sounding.
Just not very loud.
73
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New cb
Sept 8, 2018 11:29:59 GMT -5
via mobile
Post by redryder on Sept 8, 2018 11:29:59 GMT -5
Thank you for your insight. Think I will return the unit to Walmart and invest in another radio. It only costs a little more to go first class.
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New cb
Sept 10, 2018 17:52:40 GMT -5
Post by BBB on Sept 10, 2018 17:52:40 GMT -5
We have fun with those cheap Chines plastic (Maxon)"Wally World" Cobra 19 Ultra's. So many of us have them we occasionally have Cobra 19 Radio Night and get them all Jacked Up and on the air. Big power echo desk mics-Diodes clipped-multi Pill & t00b boxes I think the most we had was five OTA at the same time... haha. Good Cobra 19 times.
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