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4 month old linc 2 plus
- Thread starter Ziploc
- Start date
Brand new it's a $270 radio. You likely paid close to $300 for the work+radio I'm guessing?
Really just depends on what someone will pay.
For someone who would pay to have it tuned/converted it might be worth it to them to save $50 and they might pay $250.
As someone who does my own conversions/tuning it's hard to pay more than $200-225 for a nice used radio when I can get a new one from Amazon for $50 more.
So really just depends on who you are selling to and what that market is like.
Really just depends on what someone will pay.
For someone who would pay to have it tuned/converted it might be worth it to them to save $50 and they might pay $250.
As someone who does my own conversions/tuning it's hard to pay more than $200-225 for a nice used radio when I can get a new one from Amazon for $50 more.
So really just depends on who you are selling to and what that market is like.
Ya I had to go and check myself too. Crazy!!
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That is why I would never buy a radio from them....
Automatic Modulation Control in Solid State Transmitters
Typical Automatic Modulation Control Circuit
a small sample of the signal is fed from the audio power amplifier back to the gain controlled audio amplifier in the early stages of the input chain to prevent overmodulation on voice peaks and adjacent channel interference while providing (increased intelligibility) low levels of audio compression.
in the event that the sample exceeds the baseline established by the variable resistor the dc control voltage reduces the input to the gain controlled audio amplifier. by the same process, if the sample is below the baseline the dc control voltage is such that the input to the gain controlled amplifier is increased and all of this is done automatically the entire time the transmitter is being modulated.
the circuit operates in much the same way as the receiver AGC. low input, amplification is increased, high input, amplification is decreased.
in the case of AMC, disabling it DECREASES the average amplitude of the modulated waveform (bad) relative to the PEAK levels. with the AMC active and properly adjusted the average amplitude of the modulated waveform (good) is noticably higher when referenced to those same PEAK levels.
Automatic Modulation Control
........probably the least understood and most abused section of an am transmitter has to be without a doubt the AMC circuit. when the transmitter is modulated this circuit samples microphone input levels and controls tx audio levels being delivered to the speech stages of the transmitter. if the input level is less than optimal the gain of the circuit is increased to maintain 100% modulation (in a properly adjusted transmitter) and when input levels are excessive the gain of the circuit is decreased. the threshold point for this action is spelled out in most service manuals as 30 mV/-18dBm @ 1000 hz.. the same level is also applicable in two-tone ssb transmitter alignment for linearity @ frequencies of 500hz. and 2400 hz. where the ALC (automatic level control) levels are concerned. i have linked below to the transmitter alignment section for the Galaxy DX99V for reference purposes.
you'll also note that the same reference level of 30 mV (-18 dBm) at MIC jack is used for SSB ALC, AMC and FM deviation adjustments and that the mic. gain control for ALL of these procedures is adjusted for the maximum setting.
getting back to AMC, when mic input levels are greater than the test reference the limiting action of the AMC circuit is increased while at levels less than the reference the limiting action is reduced. when the AMC is disabled this self-regulating action is defeated resulting in everything from having to use greatly reduced mic gain settings to prevent overmodulated and distorted transmitter signals at the higher settings, now dependent on a combination of factors ranging from the output level of the particular mic in use, proximity of the operator from the microphone and to the mic gain setting itself.
with the AMC disabled and the use of microphones that are unable to provide the reference voltage levels consistently during the course of modulating the transmitter the average power output referenced over time is less than acceptable while in the same situation using microphones delivering excessive voltage levels (including amplified microphones) the average power is much higher but distortion is present for a much greater percentage of the time (during peaks) that the transmitter is modulated resulting in overmodulation of the signal and associated splatter, etc..
now why was it again that you were wanting to destroy this circuit in your equipment? are you even beginning to understand why any accomplished radio technician would rather refuse service to some customer who wanted his radio butchered in this manner instead of giving him what he "thinks" he wants based on what he read on some website or what he heard from some hack wannabe hiding his own incompetence by mouthing and proliferating pseudo technical terms like "peak and tune"?
when the output of any electronic circuit is able to produce a fairly constant, uniform level when provided with a wide range of levels at its input it is said to have dynamic range. this has everything to do with overmodulation. this inherent ability of the amc circuit is non - existent when the amc is disabled. the disabling of the amc circuit however has everything to do with overmodulation, and much much more.
when the amc is active the transistor is able to regulate the output level by self adjusting the gain of the following speech amplifier stages to compensate for lower than normal levels of mic input. when mic input levels are higher than is necessary the amc is also able to decrease the gain of the following stages to prevent overmodulation.
when the amc is disabled this self adjusting feature of the following speech amplifier stages no longer functions. the mic input levels then become critical to the amount of output of the following amplifier stages and fully dependent on maintaining a constant level at the input to maintain any uniformity in output levels. the dynamic range of the input circuit has been destroyed by the disabling of the amc circuit. it no longer is able to compensate for the nuances in speech, distance from mic, mic gain settings and other anomalies causing constantly varying signal input levels. under these conditions when input increases then output level increases accordingly and when input level is decreased then so again is the output level. this represents the total loss of any dynamic range of the input circuit. it also eliminates the possibility of maintaining highest possible average levels of transmitter output power.
https://www.angelfire.com/az/firecommunications/amc.shtml
Typical Automatic Modulation Control Circuit
a small sample of the signal is fed from the audio power amplifier back to the gain controlled audio amplifier in the early stages of the input chain to prevent overmodulation on voice peaks and adjacent channel interference while providing (increased intelligibility) low levels of audio compression.
in the event that the sample exceeds the baseline established by the variable resistor the dc control voltage reduces the input to the gain controlled audio amplifier. by the same process, if the sample is below the baseline the dc control voltage is such that the input to the gain controlled amplifier is increased and all of this is done automatically the entire time the transmitter is being modulated.
the circuit operates in much the same way as the receiver AGC. low input, amplification is increased, high input, amplification is decreased.
in the case of AMC, disabling it DECREASES the average amplitude of the modulated waveform (bad) relative to the PEAK levels. with the AMC active and properly adjusted the average amplitude of the modulated waveform (good) is noticably higher when referenced to those same PEAK levels.
Automatic Modulation Control
........probably the least understood and most abused section of an am transmitter has to be without a doubt the AMC circuit. when the transmitter is modulated this circuit samples microphone input levels and controls tx audio levels being delivered to the speech stages of the transmitter. if the input level is less than optimal the gain of the circuit is increased to maintain 100% modulation (in a properly adjusted transmitter) and when input levels are excessive the gain of the circuit is decreased. the threshold point for this action is spelled out in most service manuals as 30 mV/-18dBm @ 1000 hz.. the same level is also applicable in two-tone ssb transmitter alignment for linearity @ frequencies of 500hz. and 2400 hz. where the ALC (automatic level control) levels are concerned. i have linked below to the transmitter alignment section for the Galaxy DX99V for reference purposes.
you'll also note that the same reference level of 30 mV (-18 dBm) at MIC jack is used for SSB ALC, AMC and FM deviation adjustments and that the mic. gain control for ALL of these procedures is adjusted for the maximum setting.
getting back to AMC, when mic input levels are greater than the test reference the limiting action of the AMC circuit is increased while at levels less than the reference the limiting action is reduced. when the AMC is disabled this self-regulating action is defeated resulting in everything from having to use greatly reduced mic gain settings to prevent overmodulated and distorted transmitter signals at the higher settings, now dependent on a combination of factors ranging from the output level of the particular mic in use, proximity of the operator from the microphone and to the mic gain setting itself.
with the AMC disabled and the use of microphones that are unable to provide the reference voltage levels consistently during the course of modulating the transmitter the average power output referenced over time is less than acceptable while in the same situation using microphones delivering excessive voltage levels (including amplified microphones) the average power is much higher but distortion is present for a much greater percentage of the time (during peaks) that the transmitter is modulated resulting in overmodulation of the signal and associated splatter, etc..
now why was it again that you were wanting to destroy this circuit in your equipment? are you even beginning to understand why any accomplished radio technician would rather refuse service to some customer who wanted his radio butchered in this manner instead of giving him what he "thinks" he wants based on what he read on some website or what he heard from some hack wannabe hiding his own incompetence by mouthing and proliferating pseudo technical terms like "peak and tune"?
when the output of any electronic circuit is able to produce a fairly constant, uniform level when provided with a wide range of levels at its input it is said to have dynamic range. this has everything to do with overmodulation. this inherent ability of the amc circuit is non - existent when the amc is disabled. the disabling of the amc circuit however has everything to do with overmodulation, and much much more.
when the amc is active the transistor is able to regulate the output level by self adjusting the gain of the following speech amplifier stages to compensate for lower than normal levels of mic input. when mic input levels are higher than is necessary the amc is also able to decrease the gain of the following stages to prevent overmodulation.
when the amc is disabled this self adjusting feature of the following speech amplifier stages no longer functions. the mic input levels then become critical to the amount of output of the following amplifier stages and fully dependent on maintaining a constant level at the input to maintain any uniformity in output levels. the dynamic range of the input circuit has been destroyed by the disabling of the amc circuit. it no longer is able to compensate for the nuances in speech, distance from mic, mic gain settings and other anomalies causing constantly varying signal input levels. under these conditions when input increases then output level increases accordingly and when input level is decreased then so again is the output level. this represents the total loss of any dynamic range of the input circuit. it also eliminates the possibility of maintaining highest possible average levels of transmitter output power.
https://www.angelfire.com/az/firecommunications/amc.shtml
Umm, okay. The block diagram above doesn't really match what's been found in most SSB CB radios made since the early 80s.
There's a capacitor between the modulated audio and the detector. Sure, that's what's in a Cobra 29.
But all the RCI and Uniden SSB CB radios for decades have a DC-coupled connection between the modulated power to the transmitter final/driver and the detector circuit.
A series pair of resistors taps a tiny sample of current from the modulated B+ that comes out of the modulator circuit. The point where they join now has a smaller copy of the modulation waveform being fed to the driver/final. The emitter of a NPN transistor connects there. The transistor's emitter voltage is now "riding" along in step with your voice waveform. A trimpot sets the transistor's base terminal to a steady DC voltage. The audio waveform now riding on the NPN's emitter will fall to that magic six-tenths of a Volt lower than its base voltage if you turn the mike gain high enough. As soon as the 'down' side of your voice waveform falls to this threshold, the NPN transistor turns on, and the voltage ripples downhill to the mike amplifier's attenuator transistor. The next negative peak to come around will be reduced until the modulation is held down to the level your trimpot setting will allow. You can turn it all the way up so the peaks go all the way down to zero. Zero Volts is 100 percent negative modulation. Or you can set it the other way and never allow the negative side of your voice waveform lower than 30 percent negative modulation.
Yeah, a diagram would probably help this picture.
Anyway, just remember that the modulation limiter in a lot of radios only controls the negative half of your voice waveform. It will hold that negative modulation percentage below the setting the trimpot dictates. But it has no idea about positive peaks. Doesn't need to.
So maybe I'm really just splitting technical hairs here. I was just a bit disappointed this part of the picture got skipped from an otherwise lucid explanation.
Just one of my bad habits. Griping about what gets left out.
73
There's a capacitor between the modulated audio and the detector. Sure, that's what's in a Cobra 29.
But all the RCI and Uniden SSB CB radios for decades have a DC-coupled connection between the modulated power to the transmitter final/driver and the detector circuit.
A series pair of resistors taps a tiny sample of current from the modulated B+ that comes out of the modulator circuit. The point where they join now has a smaller copy of the modulation waveform being fed to the driver/final. The emitter of a NPN transistor connects there. The transistor's emitter voltage is now "riding" along in step with your voice waveform. A trimpot sets the transistor's base terminal to a steady DC voltage. The audio waveform now riding on the NPN's emitter will fall to that magic six-tenths of a Volt lower than its base voltage if you turn the mike gain high enough. As soon as the 'down' side of your voice waveform falls to this threshold, the NPN transistor turns on, and the voltage ripples downhill to the mike amplifier's attenuator transistor. The next negative peak to come around will be reduced until the modulation is held down to the level your trimpot setting will allow. You can turn it all the way up so the peaks go all the way down to zero. Zero Volts is 100 percent negative modulation. Or you can set it the other way and never allow the negative side of your voice waveform lower than 30 percent negative modulation.
Yeah, a diagram would probably help this picture.
Anyway, just remember that the modulation limiter in a lot of radios only controls the negative half of your voice waveform. It will hold that negative modulation percentage below the setting the trimpot dictates. But it has no idea about positive peaks. Doesn't need to.
So maybe I'm really just splitting technical hairs here. I was just a bit disappointed this part of the picture got skipped from an otherwise lucid explanation.
Just one of my bad habits. Griping about what gets left out.
73