has cobra improved on some of their problems they have had with the 200's when they 1st came out. I know the new ones have talkback, but does cobra go ahead and do all the service bulletins that are out for this radio at the factory now that this radio has been tested some??
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cobra 200gtl, new ones improved??
- Thread starter BIONIC_TEXAN88
- Start date
I have a recent one...and all bulletins were done. The adjacent channel rejection is better...but still not in the league of a grant xl or 148. Mine is a very good talker and will probably end up in my mobile It's very strong on low power...5 watts swinging to nearly 100. On high, it's set at 25-30 watts swinging to 125. Good noise blanker, decent rx and runs cool.
I get good ssb audio reports, but on 10m the channel knob and clarifier is a poor replacement for a vfo. Still...at the price point (about $200) there's not much out there to compete unless you find a good 2510 which is a better ssb rig, but not quite as good an AM talker.
YMMV,
preacherman
I get good ssb audio reports, but on 10m the channel knob and clarifier is a poor replacement for a vfo. Still...at the price point (about $200) there's not much out there to compete unless you find a good 2510 which is a better ssb rig, but not quite as good an AM talker.
YMMV,
preacherman
Skirt, that radio has a pair of 2290's so it better do at least that. I have noticed that all the 200's seem to get a very conservative tune so they last. I would still go with the 2970 or 95T.
skirtchaser said:
Call away. It was doing 3 watts to nearly 100 when I got it, but the audio was raspy and nasty. I turned the key up to 5 and have turned the modulation back until it will still hit peaks of 100, but on normal speech it's doing 80+. That isn't the way my earlier model worked...but it is what this one does.
Preacherman
skirtchaser said:
skirtchaser, I'm with you...
preacherman, do you realize that the peak voltage out of the radio would need to reach 100V in order to generate 100W PEP... How is a stock radio powered by approximately 13.7VDC able to accomplish this? I admit, I do not know anything about this particular radio, but I doubt it has a boost power supply and very high "Q" output tank. Also, the CB's modulation index would be a "4" or the modulation voltage would be 4 times greater than the carrier voltage. Distortion and splatter would be off the scale...
You should get your power meter checked.
Preacherman:
If the 200 is correctly tuned, from a 5-watt key, you should see about 20-35 PEP. That's assuming you use a steady test tone of some kind (about 500-1000 hz at about 30mv P2P will do), NOT random signals and levels as with a human voice. With a voice, the AMC will be reacting, and you will see VERY short spikes of much higher PEP.
Ken White:
100 watts PEP dissipated in the load of 50 ohms is about 71 volts developed across that load, at a current of about 1.4 amps. In the finals, which are supplied by 14 volts give or take, we'll see current and voltage shifts, but roughly the same power produced (taking into account the losses in the impedence matching and filtering circuits, and other losses such as heat). For example, lets say that both 2290's are drawing 8 amps each for a total of 16 amps. At 14 volts, thats approximately 224 watts. And the 2290's can draw more than that under normal operation. Remember that the power on both sides of any transformer is equal (in a theoretically-perfect transformer). After impedence matching and low-pass filtering (the output transformer, coils, and caps), and the other circuit losses (heat, etc), its easy to arrive at the 150-180 watts that they usually are seen to produce. This is all just simple (sort of) ohms law and basic electronics applied.
If the 200 is correctly tuned, from a 5-watt key, you should see about 20-35 PEP. That's assuming you use a steady test tone of some kind (about 500-1000 hz at about 30mv P2P will do), NOT random signals and levels as with a human voice. With a voice, the AMC will be reacting, and you will see VERY short spikes of much higher PEP.
Ken White:
100 watts PEP dissipated in the load of 50 ohms is about 71 volts developed across that load, at a current of about 1.4 amps. In the finals, which are supplied by 14 volts give or take, we'll see current and voltage shifts, but roughly the same power produced (taking into account the losses in the impedence matching and filtering circuits, and other losses such as heat). For example, lets say that both 2290's are drawing 8 amps each for a total of 16 amps. At 14 volts, thats approximately 224 watts. And the 2290's can draw more than that under normal operation. Remember that the power on both sides of any transformer is equal (in a theoretically-perfect transformer). After impedence matching and low-pass filtering (the output transformer, coils, and caps), and the other circuit losses (heat, etc), its easy to arrive at the 150-180 watts that they usually are seen to produce. This is all just simple (sort of) ohms law and basic electronics applied.
DTB Radio said:
DTB Radio, I understand the voltage will be approximately 71 Vrms, but this value is still 100 Vpk for a 100W PEP swing and for that to occur, the modulating voltage needs to be 77.63 Vpk with a carrier voltage of 22.36 Vpk - assuming a 5W carrier. Can you imagine the splatter and distortion under these conditions?
I agree that higher power can be generated, just not under the conditions described.
You're missing my point, and I can't think of a simpler way to present it. It seems like you're still trying to use the driving side of the radio (modulating section and output section before the power amp) to account for the actual power delivered to the load (after the power amp). You need to consider them seperately.
If anyone else is following this particlar discussion, sees and understands what I am talking about, and has a simpler way to present the point, please chime in.
If anyone else is following this particlar discussion, sees and understands what I am talking about, and has a simpler way to present the point, please chime in.
DTB Radio said:
I understand the secondary side of the transformer is acting as the output source to the antenna and its voltage/impedance is a function of the input, turns ratio, core material, and input/saturation current. I do understand a boost power supply is not needed, though I would use one to increase efficiency, and the transformer will work but it will need to be large to handle the currents at frequency.
My point is that a modulation index of approximately 3.47 is required for a 5W carrier and 100W PEP swing. This means the modulator will produce a severly distorted envelope which in turn means the intelligence is probably inaudible.
If you are trying to tell me that filtering will take care of this on the low level side, then the modulation index must be even higher with the distortion even worse, to generate the voltages seen at the antenna.
The transmitter/CB cannot swing from 5W carrier to 100W PEP unless the peak voltage values I quoted above are accurate and delivered to the antenna.
So are you trying to tell me that this particular CB model is capable of these specifications? If so, I would like to hook an o'scope and spectrum analyzer up to it see how clean it is.
based on the modulation index alone the signal produced by the transmitter is severely distorted and is not operating in classical am mode which requires that the Vpk at the peak of the waveform to be at or just under two times the quiescent V of the resting, unmodulated carrier. when adjusted properly this results in a carrier level that is at or slightly higher than one fourth of the PEP value when the AMC is properly adjusted.
all of the other technical aspects aside for the moment, it's another classic case of trashy am transmitter operation. don't call it an am transmitter, better yet, call it SDDSB/SC or Severely Distorted DoubleSideBand with Suppressed Carrier, way too suppressed. that's not the manner in which the manufacturer intended it to operate.
adjust the unmodulated carrier level for 25W and adjust the AMC to hold the max PEP value to just under 100W and then you'll have an AM Transmitter operating in a fairly linear fashion, then leave it alone.
all of the other technical aspects aside for the moment, it's another classic case of trashy am transmitter operation. don't call it an am transmitter, better yet, call it SDDSB/SC or Severely Distorted DoubleSideBand with Suppressed Carrier, way too suppressed. that's not the manner in which the manufacturer intended it to operate.
adjust the unmodulated carrier level for 25W and adjust the AMC to hold the max PEP value to just under 100W and then you'll have an AM Transmitter operating in a fairly linear fashion, then leave it alone.
and to continue, keeping it as simple as i can, the carrier only exists for two reasons, to act as a transport for the intelligence contained in the audio sidebands and to allow the receiver detector circuit in the listening receiver to properly demodulate the incoming signal. without getting into technicalities it stands to reason that a certain amount of carrier in relationship to the power in the sidebands is required for proper receiver detector circuit operation.
now not only do we have distortion in the transmitted signal but we also have extra distortion being added by the improperly functioning detector circuit in the listening receiver.
anyone who tells you that sounds good needs a thorough ear exam. the constant "swishing" sound added to the overall audio characteristics produced by inadequate carrier levels is annoying not only to the listener but also to those who must use consumer electronics in the near field of the generated signal and much farther out. one of the reasons for the development of Peak Envelope Power measurements in medium to high level modulated am and ssb transmitters is the energy produced as PEV equals max and the overall effects of these energy levels at or on the adjacent frequencies. that these levels had to be recognized in regard to adjacent channel / frequency interference is an indication that there are levels of power produced that are in excess of the average power output. i don't say that as a point of contention with anyone here, simply stating the facts.
ken, you're alright. thanks for your input.
now not only do we have distortion in the transmitted signal but we also have extra distortion being added by the improperly functioning detector circuit in the listening receiver.
anyone who tells you that sounds good needs a thorough ear exam. the constant "swishing" sound added to the overall audio characteristics produced by inadequate carrier levels is annoying not only to the listener but also to those who must use consumer electronics in the near field of the generated signal and much farther out. one of the reasons for the development of Peak Envelope Power measurements in medium to high level modulated am and ssb transmitters is the energy produced as PEV equals max and the overall effects of these energy levels at or on the adjacent frequencies. that these levels had to be recognized in regard to adjacent channel / frequency interference is an indication that there are levels of power produced that are in excess of the average power output. i don't say that as a point of contention with anyone here, simply stating the facts.
ken, you're alright. thanks for your input.
freecell said:
I agree, inaudible intelligence...
8)
freecell said:
freecell, I knew we would find some common ground.
why use an export if it doesnt have a VFO. like above go with the ranger or forget it. any radio can have talkback and echo.