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Modulation meter low bars on radio

undertaker said:
When I get a 2970n2 it will be from Bobscb. He does not over tune radios..
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Yeah, mine was over tuned from factory, after watching a few videos on youtube etc, and paying close attention to the before and after etc and new out of the box figures some post, I did notice a lot of ( mine inc ) that the deadkeys on hi and low AM were set too high. So in essence the mong in Malaysia or China aint doing their job properly - perhaps due to being paid peanuts and overworked, but thats another story all together LOL
 
fourstringburn said:
These newer versions of the 2970's sparked my interest so I just ordered one from Bell's CB shop. I went with the N2 version which is just the 200w mosfet version of yours. I'll be curious to see what it does out of the box. I 'm not having any of those so-called peak and tune mods just a new factory sealed box.

That brings up a question, did you have your radio peaked and tuned at time of sale or was it factory fresh?
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I would have at least had the shop do a factory tune/alignment on the radio if they have a quality tech on hand. If you just price shopped then that option is out the window. Factory fresh does not always mean properly tuned. Most factory fresh radio's are "ballparked in" at best. All of the many threads Limeybastard has started about all the little mis-tune issues with his "factory fresh" RCI only reaffirm this fact. At this point he has not done any mods to the radio but it's still not right.
 
9C1Driver said:
I would have at least had the shop do a factory tune/alignment on the radio if they have a quality tech on hand. If you just price shopped then that option is out the window. Factory fresh does not always mean properly tuned. Most factory fresh radio's are "ballparked in" at best. All of the many threads Limeybastard has started about all the little mis-tune issues with his "factory fresh" RCI only reaffirm this fact. At this point he has not done any mods to the radio but it's still not right.
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Just an FYI, RCI support, 2 emails to Ranger and 1 email to their warranty center Radioshop supply? , guess what? Those 3 emails were sent over the last 1 week to 3 weeks ago.
No responses - hilarimongous!
 
Just received my N2. I did have to adjust the AMC pot because it was too far down and the peak modulation was dropping off too soon. Now the modulation holds at it's peak until unkeyed or a long pause.

Here is a clip showing the deadkey after adjusting. The factory settings were peaking over 250 watts PEP and a low deadkey around 10w to 80w. Never could dial in a 25 watt deadkey and 200 watt PEP out of the box.

The first part shows the meter on average power and the low power scale. Notice the SWR isn't 1:1 so you have to subtract the reflected power. This is true with all meters, you have to subtract Reflected power from the Forward power to get the true power reading. The low deadkey is about 25w after subtracting the Reflected power.

The 2nd part has the meter switched to high power and Peak power and shows right about 200w after you subtract the Reflected power. After a little adjusting with the AMC, I got a nice 4:1 deadkey/swing ratio.

The RF power knob ended up in the 9:00 position.

Note: the camera is looking up at the meter at an angle so the readings appear slightly higher than what they really are.

 
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Congrats, I'll check out the video later on main computer.
Whats the low dk and hi dk on these thereabouts? 50W high and 10 or 8w low?
When you mentioned the modulation dropped quick, were you referring to the initial peak during modulation, When it then levels off?
 
fourstringburn said:
...
Here is a clip showing the deadkey after adjusting. The factory settings were peaking over 250 watts PEP and a low deadkey around 10w to 80w. Never could dial in a 25 watt deadkey and 200 watt PEP out of the box.
..
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Shooting for 200% modulation there, or you mean 25 watt carrier and 100 watt p.e.p., typo I guess
I don't doubt one could 'swing kit' a radio like that, if they wanted to.
Maybe it needs to be turned up so the average talking voice produces a closer level to 100% modulation, setting it to max at 100% could result in "yelling into the mic" lol. So think I see what you did there!

% steady modulated 100 w carrier = 400 watts PEP or 150 watts average or "heating" power. Of this 150 watts average or "heating" power, 100 watts is in the carrier, and 25 watts average power is in each of the two AM signal's sidebands
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From: https://www.w8ji.com/amplitude_modulation.htm

(what % modulation is that ratio anyway? 50 to 200 PEP is 1:4 (100%) so if we cut the carrier in half and keep the same PEP, (W/Asymmetrical "sinusoidal swing" carrier shift) that gives you 200% modulation, or more??) 25 watt carrier "swing" to 200 PEP, so "AVG SWING" (PorkChop will love that phrase) would be 25 D.K. to 75 AVG Watts?, could make an amplifier say "Yeee Haawww" for-sure, but I don't think your aiming for +200% modulation..)
 
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fourstringburn said:
That was just quick out of the box figures initially. I was trying to see if I could find a 4:1 ratio by turning the RF knob and I couldn't. A 4:1 ratio the is commonly accepted as 100% modulation.

This is a 200 watt radio and OOTB it was doing over 250 watts even with the dead key down some. As the PEP cam down, so did the dead key. But the ratios were never close to a 4:1.

After some simple adjustments the PEP came down to about 200w with the dead key at 25w.

No more power adjustments are necessary.
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I'm glad you got it sorted out, let us know how you feel about the quality after some time!
 
Thanks Leapfrog, you made realize my figures were wrong!

Been a long week and I can't do math!!!

I just realized it's 50 watts dead key to equal 4:1 with 200 watts PEP.

Luckily, I was able to turn up the RF pwer knob all the way up and just came in with 50 watts deadkey and the PEP still peaks just over 200 watts.
 
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I say it's because the AMC adjustment is on the edge of the threshold from staying open. I turned this up to where it holds. It can be turned up and it will cause the modulation to bring up the peak some yet the modulation limiter circuit is still active.

Typical radio hack jobs cut the modulation limiter which essentially carries the modulation well beyond it's limits. This gives radio's that Big AM sound but also can cause distotion and splatter across many close in frequencies.
 
fourstringburn said:
I say it's because the AMC adjustment is on the edge of the threshold from staying open. I turned this up to where it holds. It can be turned up and it will cause the modulation to bring up the peak some yet the modulation limiter circuit is still active.

Typical radio hack jobs cut the modulation limiter which essentially carries the modulation well beyond it's limits. This gives radio's that Big AM sound but also can cause distotion and splatter across many close in frequencies.
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With cutting , do the folks actually remove the complete potentiometer from the board?

Did you notice the vr dead key pots and amc were clockwise to increase resistance ?
 
Limeybastard said:
With cutting , do the folks actually remove the complete potentiometer from the board?

Did you notice the vr dead key pots and amc were clockwise to increase resistance ?
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Depends on the model of radio

Most AM only Cobra/Uniden it is a diode to clip/cut or (add 1K Ohm resistor somewhere)
Most export radios they pull out a transistor or two and/or clip a resistor

On some old models I have seen the VR removed and changed for a resistor (Cobra 21X)

On some radios like Cobra 25/29 a cap/resistor swing kit can allow the radio to over-modulate even without clipping anything, depends who set it up.
 
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