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UNIDEN 68XL SWINGING !!

cobra

I have never own one of these radio's, and I am sure they are a excellent radio for what they are.But I don't get all the big discussion about thirty or fifty watts.If I was going to run one of these I would simple send it down to richard and have him do a complete alignment, set the modulation for 100%,deadkey about 3 watts and simply buy a small amp.Has to sound better than a wacked, hacked,volted, ripped apart radio.And when you flip the switch they will never hear that fifty watt cobra.
 
AA1QD said:
I don't care what is done to a cobra 29, unless you can get at least half the peak average power for a carrier, IT IS NOT CLEAN! The formula doesn't change. And again 50 watts pep, so? What is it doing RMS? !
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Why would'nt it be clean? Its not going to start spitting out harmonics when its undermodulated.... Undermodulated will put out less IMD and have a clearer signal that a fully modulated radio..
Why would you think that if the rf output is undermodulated it will be dirty?

Average and RMS are 2 different things... RMS measurement is is just a straight AC measurement. Its a measurement of just the AC sinewave.
It sounds like your fairly familiar with RMS and average reading.... you should be able to guage fairly quicky what a 30 watt carrier swinging to 50 watts will do average.... It will be 30 watts rms... On a through line sampling meter thats reads RMS ,if your carrier is 1/2 of the forward swing, the needle won't move. If your under that then the needle swing backwards.... if your over that it will swing forward.

My first carrier reading as taken on a Telewave 44a.. that meter doresn't do peak so I switched to a termaline for the peak readings.

Doing a pill mod to any radio is as clean as any cb amp of the same class (with exception of the odd few)... there is no difference. The higher the modulation level the more possibility of intermodulation distortion and harmonic mixing. It doesn't increase as the modulation level goes down... it increases as the modulation increases. A overmodulted radio will put out more crap than an undermodulated radio. Running undermodulated is cleaner sounding.

This is a sd1446 I'm using.... its not crazy to think that the transistor can put out that amount of power cleanly and without overdriing it. A 1 pill sd1446 amp will do upwards of 90 to 100 watts.... 30 watts swinging to 50 watts clean is relativly easy for that transistor to do. Its not outrageous to think that you can get 50 watts peak out of an sd1446 clean.

I still don't know what formula you talking about that says harmonics, IMD and other crap increases and your modulation level decreases.

These radios are done for truckers that can't run amps in their trucks or don't want to bother with it since they are switch seaters. You can always get the power externally... but there is a reason for these radios. We do these mods because we know how to... and people want them for specific reasons.
 
He said around a 3 watt carrier swinging to 50 pep!!?? How the hell can that radio be under modulated? The wave form MUST be obliterated with that kind of swing. I'm so over this whole topic, it's just silly at this point. :roll:
 
been biting my tongue for as long as i could, but, eventually you bite through & just gotta speak. :twisted:
WHAT exactly is the allure of a 50 watt CB radio????? 10 watts, 50 watts, 150 watts, 300 watts???? my radio with just a few watts of carrier-enough to fully excite the driver stage/box-and crystal clear, clean LOUD audio-as per the EARS of some of the best in the biz-a 'scope never told ANYBODY how the audio sounds!-and any further amplification devices in line-are what almost EVERYBODY is after. they are just using their 25-40-50-70-150-whatever watt radio to DRIVE a bigger box. if EVERYBODY would stop buying into these STUPID mods, just get the AUDIO to sound good, then AMPLIFY the crap out of the wattage, the scam artists would be out of business, except for those crappy 600 watt amps that do 250, AND, you would probably be able to UNDERSTAND the modulation entering your receive from more radios then you ever thought possible.
i just may have to return to the penny-place :x :twisted: :? :moon :peace :rknrl :nutzo :hrsdedel :frky :cuss :dahtman :colshd :bgcry ^)( %&* :wow :bounce :stupid :lol :naughty :mrgreen:

sorry....had to get that outta my system
 
I couldn't agree more, if it sounds good run it. But don't sit there and try to blow smoke up every ones woohoo about how clean the signal is. Personally I really don't care if my set up isn't linear, as long as I'm maul droppin. I would say anyone who has went home with a trophy from any of the major breaks was not linear either. It is what it is.
 
loosecannon said:
i wonder if he takes ketchup with his sh!t sandwich.LOL

just kidding nightrider, have you sent the radio out yet?
inquiring minds want to know.
loosecannon
Click to expand...

no problem dude, no i havnt sent the radio yet, my supplier decided not to answer his phone or email, guess he doesnt want to make money, anyhow i got a 68 coming my way, will be here in a few days, then off to dbt for testing, other than that been really busy here, not much time for radio at all
 
Ok, the radio arrived today. Before opening the case, here's what I saw. At 14.2 volts, I see 10 watts key on a Bird 4314B, with peaks to about 30-32 roughly. My Wavenode system, which matched the Bird for carrier reading and which seems to capture max peaks more accurately (non-mechanical system), shows it just kissing 40 watts on max peaks. Audio quality I would have to call poor. Its loud, but the AMC circuit is not engaging, so there is severe clipping in the output of the audio chip. If you turn down the mic gain, it clears up, but you lose the loudness.

Opening the case revealed the following:

Final = 2SC2078

Mods included removing the AMC capacitor, and what appears to be the CB Retards mod for variable power without the resistors in the ground line of the variable (glorified mod kit, basically)

The work that was done was done pretty well, with no gobs of solder or dangling wires, and with heat shrink insulating the varibale power mod.



Over-all conclusion is that the radio is no better than other's I've seen with the same kind of work. Due to both the final being a typical stock final, and the disabled AMC, the radio's top performance potential isn't reached.

Sorry to disappoint, Nightrider, but I gotta call'em like I see'em.
 
DTB Radio said:
Ok, the radio arrived today. Before opening the case, here's what I saw. At 14.2 volts, I see 10 watts key on a Bird 4314B, with peaks to about 30-32 roughly. My Wavenode system, which matched the Bird for carrier reading and which seems to capture max peaks more accurately (non-mechanical system), shows it just kissing 40 watts on max peaks. Audio quality I would have to call poor. Its loud, but the AMC circuit is not engaging, so there is severe clipping in the output of the audio chip. If you turn down the mic gain, it clears up, but you lose the loudness.

Opening the case revealed the following:

Final = 2SC2078

Mods included removing the AMC capacitor, and what appears to be the CB Retards mod for variable power without the resistors in the ground line of the variable (glorified mod kit, basically)

The work that was done was done pretty well, with no gobs of solder or dangling wires, and with heat shrink insulating the varibale power mod.



Over-all conclusion is that the radio is no better than other's I've seen with the same kind of work. Due to both the final being a typical stock final, and the disabled AMC, the radio's top performance potential isn't reached.

Sorry to disappoint, Nightrider, but I gotta call'em like I see'em.
Click to expand...

if you didnt call like you see it, i would be pissed off, thanks for the fair evaluation, let me ask you this what would need to be done for the radio to meet its top performance potential ???
 
Well, going by past experience with that model, I'd install either the 2SC1969 final, or the ERF2030 (and its needed bias control piece), and re-install the AMC cap. For transmit adjustment purposes, you can leave the AMC pot all the way up until you're finished tuning the driver and final circuits, then reset it for best loudness and least distortion. As for the actual tuning of the driver and final circuits, you'll need to play with cap values and coil adjustments a bit there. I've seen different units of the same model show slightly different results with the exact same values used. As for the variable power idea, its fine, but I'd lose the big electrolytic cap and use a .01uf isntead. That will keep the little bit of garbage out that seems to show up in those radios when using any kind of resistor in the driver's collector circuit. I'd also place a resistor inline with the ground side of the variable POT to set a minimum deadkey. 0 deadkey is a bad thing. Beyond that, its going to boil down to how much effort and care you put into tweaking for best results.
 
Which cap is removed? What value?
I did a guys 25 from work, and I noticed a cap appeared to be missing. Looked like it would've been a radial electolytic.
L8 was a bit bent up and a jumper was bent also, made me think this was some sort of feeble attempt at a tune.
 
74IN said:
Which cap is removed? What value?
I did a guys 25 from work, and I noticed a cap appeared to be missing. Looked like it would've been a radial electolytic.
L8 was a bit bent up and a jumper was bent also, made me think this was some sort of feeble attempt at a tune.
Click to expand...

I'm not at the shop to look at a part #, but its the small 1uf cap that brings the audio from the transformer to the rest of the AMC circuit. Its near the AMC control.
 

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