Brand new radio. Swings backwards

[DarkEyes]

Just got a Uniden BC 980 to use for a extra radio. Thing is it swings backwards on my meter on adv setting and that's with the truck running. I have questioned this same meter before so I'm not sure what to think. SWR on the radio is 1.00 across the band and is just a bit higher using the meter 1.2 on 20 1 on 1 and 1.4 on 40. LMR400 coax installed in a 2010 pete. K40 antenna. My other radio Magnum S9 just does not swing on the meter in adv and its hooked up to the battery with 8guage wire. I used the stock cb terminals to hook up the 980. Meter is Redman brand. I think I just need to get a antenna antalizer and forget the rest. IDK.. I'm ready to do any test someone might have. Thanks

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[ke4cci]

Dark Eyes,
Sounds like a grounding issue to the radio. Check your power cable to radio.

['Doc]

I'm not familiar with the term 'adv', what does it mean?
- 'Doc

[rrtdave]

If you are using the meter on your radio, check your SWR/power/Modulation switch. If you are on SWR, your transmission will swing to the left.

[231]

So tell us about this new radio...did you have any modifications done to it? I'm not familiar with Redman's meters...nor what adv means. I'd think it means "advanced" settings but what do they include specifically? If you don't know and your S9 doesn't swing at all, I'd question it's actual function. If you are getting good reports I'd probably not worry too much about it. Sounds like an analyzer will tell you what you already know anyway...but it never hurts to throw one on to see.

Good luck.

231

[DarkEyes]

Sorry it took so long to reply. Got busy driving and forgot about posting this. Adv means average. Radio has not been opened. Reports are good. I'm just gona leave it alone until I get or find someone with a antenna analyzer.
Thanks for the replies.

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[petriach]

What is happening is your signal modulation is asymmetrical.

Full page I pulled this from:

The most common type of RF power meter is the "average-reading" meter. For our purposes RMS and average are the same. There are meters that are "peak-reading" meters as well. Those are sub-divided into two catagories: powered, peak-reading meters; and unpowered (aka pseudo) peak-reading meters. Remember, all these meters are inaccurate in one way or another; some are more inaccurate than others.

Before we continue, we should look at how the average (or RMS) measurement is made.

If you'll recall, when modulation is added to a carrier the peak envelope voltage increases and decreases by the same amount. For example, a CB that produces a 4 watt carrier will have a peak envelope voltage of 20. At 100% positive and negative modulation the peak envelope voltages will be 40 and zero respectively. Averaging those two voltage measurements brings us right back where we started at 20 volts. Do you see what happened? As far as our measurements are concerned, the AVERAGE wattage doesn't change when modulation is added as long as the positive and negative modulation swings are equal and opposite. That's how average and RMS reading meters work. They are average-reading VOLTMETERS that read out in average or RMS watts. In other words, the positive and negative modulation swings cancel each other out resulting in an average wattage reading.

This brings up an interesting point: What happens when the positive and negative modulation swings are not equal and opposite (aka unsymmetrical modulation)? The answer is that as modulation is added the meter reading will swing toward the dominant modulation type. For example, let's say we have a CB whose carrier is set to 6 watts. Let's say that this particular radio can acheive 100% negative modulation, but can only acheive 50% positive modulation. When modulation is added there is a net LOSS of average power because the negative modulation swings decrease the carrier power more than the positive modulation swings are increasing it. An average-reading meter will show the net loss in average output when modulation is added. This type of situation is very common in CB radio. Decreasing average power when modulation is added is commonly known as "backward swing." It happens when the carrier (dead-key) wattage is increased too much. In that situation there isn't enough audio power to symmetrically modulate the carrier. It also happens when the carrier drive to an amplifier is too high.

[MDYoungblood]

I have not had the privilege of opening one but have seen a couple of videos. I believe the radio may have a bad voltage regulator, as modulation is applied the wattage drops. I have seen that it has a clip that holds the regulator in place against the side of the case, no grease (heat sink compound) is used to help with heat transfer making it prone to failure.

3's

Greg