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Cobra 148- Much Higher Performance Receive Setup Than Shottky Diode Receive Mod
- Thread starter cbphreaker
- Start date
Didn't have a small 10k pot so disregard the temporary pot. Volume is not blaring but it is not quiet in level. Still need to align my receive but with a missed connection with my board , a quick jumper fixed that issue and detector worked first time. Only slight mod I would do is add some tone control for my liking but so far circuit works. Will keep testing, credit again to CBphreaker. Thanks homie for the circuit. Also working on a few D104 desktop mods. Dual JFeTs are in the plans.
Is the jumper you describe on the solder side of your custom pc board? Could you post a picture if it is, thank you 711.
Thank You CBPhreaker!
Thank You LC and the others who are contributing to this mod/thread.
I'm glad to see that the simple schottky receiver modification w/ 2999 transistor swap is not the end all be all mod, and this thread shows that much better things can be accomplished when people work together and share information.
It's make me truly happy to be in this community and part of this hobby.
Thank You CBPhreaker!
Thank You LC and the others who are contributing to this mod/thread.
I'm glad to see that the simple schottky receiver modification w/ 2999 transistor swap is not the end all be all mod, and this thread shows that much better things can be accomplished when people work together and share information.
It's make me truly happy to be in this community and part of this hobby.
@Frog I was in a rush late at night to get this board made and in 10 minutes , I got both files done and sent off but missed the supply voltage to the input of the non inverting opamp of the first stage. I think I might widen the audio buffer a little more but will continue to play with this board first. Rev 2 will be surface mount and include a lm386 as the audio amp. Want to play with the noise blanker to get some functionality of the front pane back.
Great thread gents. Please keep up the good work. This one has been a good mod it appears for those wishing to perform a mod similar to this one. Would be sweet if someone made this particular board and sold it for the 148, at a low cost that is. Not rob yourself, but don't rob others with a type deal. In sure someone here has the time and skills to make these and actually tailor them to the needs or wants from potential buyers.
Or keep it like it is. A free schematic for those capable of building it and installing and re tuning radio if needed.
Makes you wish there were more good techs out there that weren't either pediphiles or just plain robbing people!!!
I can dream can't I LOL. I don't own my 148 any longer and I kick myself in the arse often for letting the scammer tech that for it from me should be out of business as well. He is supposedly a service center for kenwood radios. I wouldn't let this shit head touch a kids walkie talkie, let alone a CB ever again. This is a gent around the Ormond Beach, FL area right on the ocean on A1A. May be in a place called Ormond by the Sea as well. I can't remember the name of the place, it's so small of you aren't looking for it, you'll pass it by LOL. At any rate he took my 148 to fix it, which I know what the issue was, it needed to be recalled and solder joints repaired as well as removal of an echo board. If he couldn't do the work, which is what he told me he pretty much, he tried for hours and gave up. He offered to give me some credit for it and get a newer 148. I took the money and left the radio as it was in pieces and this was after waiting like a month or 2 for it already. Lesson learned!!!! At any rate, sorry for the rant and text block.
Again, Thx cbphreaker and the rest of you gents as well for this one. Maybe it could be made into a sticky?? How about it mods? This seems like a good thread Ana good info, let's make it a sticky.
Good day, 73 and God Bless to All.
Sean.
Or keep it like it is. A free schematic for those capable of building it and installing and re tuning radio if needed.
Makes you wish there were more good techs out there that weren't either pediphiles or just plain robbing people!!!
I can dream can't I LOL. I don't own my 148 any longer and I kick myself in the arse often for letting the scammer tech that for it from me should be out of business as well. He is supposedly a service center for kenwood radios. I wouldn't let this shit head touch a kids walkie talkie, let alone a CB ever again. This is a gent around the Ormond Beach, FL area right on the ocean on A1A. May be in a place called Ormond by the Sea as well. I can't remember the name of the place, it's so small of you aren't looking for it, you'll pass it by LOL. At any rate he took my 148 to fix it, which I know what the issue was, it needed to be recalled and solder joints repaired as well as removal of an echo board. If he couldn't do the work, which is what he told me he pretty much, he tried for hours and gave up. He offered to give me some credit for it and get a newer 148. I took the money and left the radio as it was in pieces and this was after waiting like a month or 2 for it already. Lesson learned!!!! At any rate, sorry for the rant and text block.
Again, Thx cbphreaker and the rest of you gents as well for this one. Maybe it could be made into a sticky?? How about it mods? This seems like a good thread Ana good info, let's make it a sticky.
Good day, 73 and God Bless to All.
Sean.
I'm glad to have posted this. It's nice to see ops who choose to break the barrier of normality and refuse to accept eBay mods such as the shottky diode detector.
Although I haven't posted in a minute, I have been following along with people's progress which lit a fire under my behind to finish two other type's of detectors; the infinite impedance and PLL.
Let me state, about the infinite impedance detector, before anyone tell's me there is no such think as infinite. I know, it's the name given to a type of detector which has a high input impedance, or more correctly stated - higher than the impedance of a diode detector - by far.
However, these circuits are a tale/post for another time. The spotlight is on the peep's enjoying a sweet build and it is my intention to congratulate everyone who has walked down this path to better receive.
CBphreaker
Although I haven't posted in a minute, I have been following along with people's progress which lit a fire under my behind to finish two other type's of detectors; the infinite impedance and PLL.
Let me state, about the infinite impedance detector, before anyone tell's me there is no such think as infinite. I know, it's the name given to a type of detector which has a high input impedance, or more correctly stated - higher than the impedance of a diode detector - by far.
However, these circuits are a tale/post for another time. The spotlight is on the peep's enjoying a sweet build and it is my intention to congratulate everyone who has walked down this path to better receive.
CBphreaker
Just to upset my progress, I have reduced the gain of the second opamp to drive preamp based on the LM386 opamp. Really simple circuit and will drive any CB sealed out there. Haven't had a chance to try it on my 6x9 low end speaker but it does sound better. I'm redoing my CB/PA switch to A/B the PDD and Goldfinger modded stock setup. I still need to mod the ANL for more action but still trying to get used to the sound
IT all there, buried in the posts... and I found some other stuff that can be added in that may help others in the future.
Granted the thread "died" a while ago, but the technology for it hasn't - in fact it's expanded.
I attached a PDF for those interested.
If anyone remembers the ST function - this is the EXPANSION side of it.
IT uses an Op Amp - to work as a THRESHOLD Detector - both Inputs are used and an adjustment is made in the install for the threshold adjust to work only on signal PRESENCE - it's several steps above an ANL circuit.
It installs in the IF section - using IF signal as the medium. The IF section is always working - producing a quiet low-noise carrier signal, when IF gets an RF amp signal - the IF section merely amplifies the "image" - this circuit takes for granted the IF carrier presence and uses it to self-bias and stay quiet - no signal - until a signal is detected, rectified and then amplified and sent to the next stage. IT uses the detected audio for the amplification process.
This is different than ANL derived, which uses AGC derived bias to adjust the "window" or gate so the signal can be received. This is much like the Squelch circuit - without the silence - just the ambient level noise hiss that once a signal has been detected - it is amplified..
When using Schottky - the low-level signal is still low-level and has to be "pulled out" or extracted from the ambient noise still passing thru the diode.
Where Schottky is used with AGC function - the AGC can provide a dynamic headroom by pushing down the amplifiers gain first, then allow the louder signal and better IF detection figures to be obtained instead.
In fact, with minor rework, this can be applied with an ANL filter (not exact but in theory) and can also be self-guiding using AGC feedback to adjust the OP amp gain - perhaps the other half of that Dual Op amp can function as such in this.
Give me some time to think about this...
:+> Andy <+:
Granted the thread "died" a while ago, but the technology for it hasn't - in fact it's expanded.
I attached a PDF for those interested.
If anyone remembers the ST function - this is the EXPANSION side of it.
IT uses an Op Amp - to work as a THRESHOLD Detector - both Inputs are used and an adjustment is made in the install for the threshold adjust to work only on signal PRESENCE - it's several steps above an ANL circuit.
It installs in the IF section - using IF signal as the medium. The IF section is always working - producing a quiet low-noise carrier signal, when IF gets an RF amp signal - the IF section merely amplifies the "image" - this circuit takes for granted the IF carrier presence and uses it to self-bias and stay quiet - no signal - until a signal is detected, rectified and then amplified and sent to the next stage. IT uses the detected audio for the amplification process.
This is different than ANL derived, which uses AGC derived bias to adjust the "window" or gate so the signal can be received. This is much like the Squelch circuit - without the silence - just the ambient level noise hiss that once a signal has been detected - it is amplified..
When using Schottky - the low-level signal is still low-level and has to be "pulled out" or extracted from the ambient noise still passing thru the diode.
Where Schottky is used with AGC function - the AGC can provide a dynamic headroom by pushing down the amplifiers gain first, then allow the louder signal and better IF detection figures to be obtained instead.
In fact, with minor rework, this can be applied with an ANL filter (not exact but in theory) and can also be self-guiding using AGC feedback to adjust the OP amp gain - perhaps the other half of that Dual Op amp can function as such in this.
Give me some time to think about this...
:+> Andy <+:
Don't Panic - just adding more stuff for expansion of options...
One of the topics of this was the AGC and ANL problems.
This upload is from a site that is a repository of Ham, or Amateur - radio ideas, support circuits and some good tutorials.
This is just an upload not necessarily for discussion, but it is something I found...
One of the topics of this was the AGC and ANL problems.
This upload is from a site that is a repository of Ham, or Amateur - radio ideas, support circuits and some good tutorials.
This is just an upload not necessarily for discussion, but it is something I found...
Hi Robb!
Well, not to make this too complex, I'm still gathering up ideas on this.
Was kinda' thinkin' about the TL082's other half scenario. So if there is a particular Diode you want to use or have me try out I hope I can locate it locally.
"the Other Half" scenario deals with AGC control and possibly an alternate of the ANL filter - being tied into the loop as an active filter with output.
What are some potential problems are related to the AGC? By what I read - I think you guys had that sorted out but were unable to use ANL like you'd wanted.
Looking back at the schematic, one of the problems with the ANL being switched in, was the lack of a bias on the circuit that it used. It's essentially a hi-cut / low-pass (you pick) filter and used the negative bias generated by the diodes (D21 D22) to power it - it used the carrier in the IF as a working power (bias) and the Audio passed thru this circuit - filtered by the bias the carrier power presented - the radios' own power (RX side) provided a recovery level to recoup audio that would otherwise be lost as it tried to pass thru this circuit. As a side note, it is why the cap is reversed and a bias resistor network is used to provide a working effort or impedance - the audio level is supposed to be fine tuned by the AGC response and it's feedback loop back to the front end of the RX strip where the signal arrives (PIN diode section D68 R43) and the IF / RF strip section amplifies that result - to the cycle continues. (your results may vary).
So what Id like to try in this circuit - to try incorporating the ANL section - and all you have to do is "insert" the circuit - the idea here is to generate a circuit that can apply a punch to the audio but keep the active filter.
The TL082's other half part, would be recreating the audio path only for the Negative going AGC power for use in radios like the Cobra 29 or PC68 - which use a rectified negative-going bias against a voltage divider that is the AGC the radio applies to both the IF and RF PIN diode sections. The 148 style radios already have that and the 1N60s' do nothing more than power that active filter behind them.
Return back to the paragraph above - the ANL side of it still needs a negative going power so that ANL circuit too, is supposed to "float audio" at a level of power that can achieve voltage potentials that are below foil board ground levels. Much like the Negative going diode circuit used in the same AM only radios - they don't need the voltage bias, just the audio and if sent thru and rectified in a reverse - bias derived diode network - you get a negative voltage that can be recovered for this bias purpose - this is what my initial ideas are to apply this circuit in this thread, with a separate network tied to the other half of the op amp to regenerate the two 1N60 negative bias configuration from the recovered audio from the output of the first half. This amplifier wouldn't be able to generate a negative bias without some form of a signal - but what it can do generate an offset that can SINK current from the AGC voltage divider network (in a typical AM only radio) in small amounts - like a siphon. IF that can't be done, we can still modify the resistor network in a fashion so that the audio presence works like the regulator for the air noise - like a noise gate - only used as audio detected is amplified.
Had some work come in so I had to fix some little fires and lost out on getting the time window to go shopping at a local Electronics Supply store here nearby. I was hoping to breadboard up a working prototype of what you folks had.
What Uniden/Cobra and Midland and all the others use, was a bias that went below foil board ground - in doing so - helped remove spikes that would have been buried in the noise floor and covered up recoverable audio - they allowed those diodes to generate and detect two sets of power, a carrier based bias power, and audio envelope derived from it - the two were used in the active filter behind it, as a method to remove the spikes in the audio signal envelope - the cap was oriented in a way to accommodate the negative bias voltage the diodes would generate and power this filter. A high impedance voltage feed was used to help the cap and resistor network recovery - there are also a separate resistor divider network that used the DIFFERENCE this negative potential is - and the positive potential supplied by the radio - and the ANL diode passed the differences as an audible result - note the word Audible - doesn't always mean it was a clean signal - it's was an audible signal.
If you had done one, I'd like to know what issues came up?
:+> Andy <+:
Well, not to make this too complex, I'm still gathering up ideas on this.
Was kinda' thinkin' about the TL082's other half scenario. So if there is a particular Diode you want to use or have me try out I hope I can locate it locally.
"the Other Half" scenario deals with AGC control and possibly an alternate of the ANL filter - being tied into the loop as an active filter with output.
What are some potential problems are related to the AGC? By what I read - I think you guys had that sorted out but were unable to use ANL like you'd wanted.
Looking back at the schematic, one of the problems with the ANL being switched in, was the lack of a bias on the circuit that it used. It's essentially a hi-cut / low-pass (you pick) filter and used the negative bias generated by the diodes (D21 D22) to power it - it used the carrier in the IF as a working power (bias) and the Audio passed thru this circuit - filtered by the bias the carrier power presented - the radios' own power (RX side) provided a recovery level to recoup audio that would otherwise be lost as it tried to pass thru this circuit. As a side note, it is why the cap is reversed and a bias resistor network is used to provide a working effort or impedance - the audio level is supposed to be fine tuned by the AGC response and it's feedback loop back to the front end of the RX strip where the signal arrives (PIN diode section D68 R43) and the IF / RF strip section amplifies that result - to the cycle continues. (your results may vary).
So what Id like to try in this circuit - to try incorporating the ANL section - and all you have to do is "insert" the circuit - the idea here is to generate a circuit that can apply a punch to the audio but keep the active filter.
The TL082's other half part, would be recreating the audio path only for the Negative going AGC power for use in radios like the Cobra 29 or PC68 - which use a rectified negative-going bias against a voltage divider that is the AGC the radio applies to both the IF and RF PIN diode sections. The 148 style radios already have that and the 1N60s' do nothing more than power that active filter behind them.
Return back to the paragraph above - the ANL side of it still needs a negative going power so that ANL circuit too, is supposed to "float audio" at a level of power that can achieve voltage potentials that are below foil board ground levels. Much like the Negative going diode circuit used in the same AM only radios - they don't need the voltage bias, just the audio and if sent thru and rectified in a reverse - bias derived diode network - you get a negative voltage that can be recovered for this bias purpose - this is what my initial ideas are to apply this circuit in this thread, with a separate network tied to the other half of the op amp to regenerate the two 1N60 negative bias configuration from the recovered audio from the output of the first half. This amplifier wouldn't be able to generate a negative bias without some form of a signal - but what it can do generate an offset that can SINK current from the AGC voltage divider network (in a typical AM only radio) in small amounts - like a siphon. IF that can't be done, we can still modify the resistor network in a fashion so that the audio presence works like the regulator for the air noise - like a noise gate - only used as audio detected is amplified.
Had some work come in so I had to fix some little fires and lost out on getting the time window to go shopping at a local Electronics Supply store here nearby. I was hoping to breadboard up a working prototype of what you folks had.
What Uniden/Cobra and Midland and all the others use, was a bias that went below foil board ground - in doing so - helped remove spikes that would have been buried in the noise floor and covered up recoverable audio - they allowed those diodes to generate and detect two sets of power, a carrier based bias power, and audio envelope derived from it - the two were used in the active filter behind it, as a method to remove the spikes in the audio signal envelope - the cap was oriented in a way to accommodate the negative bias voltage the diodes would generate and power this filter. A high impedance voltage feed was used to help the cap and resistor network recovery - there are also a separate resistor divider network that used the DIFFERENCE this negative potential is - and the positive potential supplied by the radio - and the ANL diode passed the differences as an audible result - note the word Audible - doesn't always mean it was a clean signal - it's was an audible signal.
If you had done one, I'd like to know what issues came up?
:+> Andy <+:
Shadetree Mechanic
Delaware Base Station 808
To add some more to this...
When you research this part of the "detector" - I find some information but much of it is either speculation or just talk about how diodes are lousy at audio reproduction - yet we use them everywhere in a radio .
Part of the problem in this - I feel we are reinventing the wheel - but in such a fashion that until now - not much what ever known about the how or why this way is used so many radios. So the wheel just needs to be more understood.
One of the complaints in the thread was what the audio did when the circuit was installed and working - then the ANL was turned on.
Did anyone notice or understood why the audio "died"?
Because you removed the very power sources the radio uses to balance the audio as an AC component in an active filter being powered by the IF power that contains the Carrier and Envelope - we are extracting the envelope and what is left is a constant DC sourcing of carrier power that is the RF signal - brought to IF level as an Image and the diodes are actively providing both - but the power that is present - is audio and a DC component.
The NB side, took care of many positive going spikes the diode network was able to detect and thru processing and amplification - removed...
You remove the detector diodes, you took away that circuits only power source to filter the audio - you engage the ANL - the radio "dies" - why? You forgot to put gas back in the car - the very engine it needed to do work . So the diode that is the ANL limiter part of it - simply attempts to fill in the missing energy in that circuit. Any Audio present is rectified and sent in there - there is nothing in there so it's (the circuit) has to replenish what the D21/D22 would have provided. Removing the diodes - it took away the power source and turning on ANL rerouted audio and sent it in to be filtered out by a cap and any DC energy was absorbed in the resistor network. Because the carrier it rode in on was removed it literally sucked all the audio down into that rabbit hole...
The spikes and audio present together - the negative energy and circuit design let the audio float across a cap / resistor network and as it did - the extra energy that was higher in potential or less than potential - at that given moment in time - was either added to the caps ability to store energy or removed from the cap because the diodes did their job in providing the "well" and a hole deep enough to put the water in- so the cap can offer to replenish the missing info.
The cap is a smoothing filter - so your result was audio that had less treble - more bass.
So if we know that - why not reverse the ANL diode and cap - reinstall the power to the ANL circuit by just reversing the polarity of the diode, the cap and then look at the 1 Meg resistor and think about allowing a power to flow thru this circuit all the time - we just need to "up" the power flow - instead of 1 Meg resistor - try lowering it to increase the power level for audio to pass thru - like 470K or 330K resistor once all the parts are reversed and try it that way?
You can even change the cap used, to a series of caps of various values - Electrolytic or not, some like 0.22uF or 0.1uf and even 1, 0.47uF - Tantalums give one effect, but Disc and Mylar another - mix and match to see if the caps can handle the various tones and their reactive elements adding and subtracting - versus tied to one value and it's particular character?
The method should work, the issues around "crappy" audio are due to filtering out spikes that are altering the audio waveform - the filter tries to fill in gaps but it cannot recreate missing information caused by the spikes overlay in the embedded audio. It limits it - trims it off but can't "insert data here" - your ears have to process the rest.
The removal or bypass, you can hear how well the radios receiver is, which for many is acceptable and nicely done. But we can't remove the line noise or other things the NB circuit has to take over and remove - again it punches holes in the signal and you're left with missing information.
So anyhoo...Hi How are you?
:+> Andy <+:
When you research this part of the "detector" - I find some information but much of it is either speculation or just talk about how diodes are lousy at audio reproduction - yet we use them everywhere in a radio .
Part of the problem in this - I feel we are reinventing the wheel - but in such a fashion that until now - not much what ever known about the how or why this way is used so many radios. So the wheel just needs to be more understood.
One of the complaints in the thread was what the audio did when the circuit was installed and working - then the ANL was turned on.
Did anyone notice or understood why the audio "died"?
Because you removed the very power sources the radio uses to balance the audio as an AC component in an active filter being powered by the IF power that contains the Carrier and Envelope - we are extracting the envelope and what is left is a constant DC sourcing of carrier power that is the RF signal - brought to IF level as an Image and the diodes are actively providing both - but the power that is present - is audio and a DC component.
The NB side, took care of many positive going spikes the diode network was able to detect and thru processing and amplification - removed...
You remove the detector diodes, you took away that circuits only power source to filter the audio - you engage the ANL - the radio "dies" - why? You forgot to put gas back in the car - the very engine it needed to do work . So the diode that is the ANL limiter part of it - simply attempts to fill in the missing energy in that circuit. Any Audio present is rectified and sent in there - there is nothing in there so it's (the circuit) has to replenish what the D21/D22 would have provided. Removing the diodes - it took away the power source and turning on ANL rerouted audio and sent it in to be filtered out by a cap and any DC energy was absorbed in the resistor network. Because the carrier it rode in on was removed it literally sucked all the audio down into that rabbit hole...
The spikes and audio present together - the negative energy and circuit design let the audio float across a cap / resistor network and as it did - the extra energy that was higher in potential or less than potential - at that given moment in time - was either added to the caps ability to store energy or removed from the cap because the diodes did their job in providing the "well" and a hole deep enough to put the water in- so the cap can offer to replenish the missing info.
The cap is a smoothing filter - so your result was audio that had less treble - more bass.
So if we know that - why not reverse the ANL diode and cap - reinstall the power to the ANL circuit by just reversing the polarity of the diode, the cap and then look at the 1 Meg resistor and think about allowing a power to flow thru this circuit all the time - we just need to "up" the power flow - instead of 1 Meg resistor - try lowering it to increase the power level for audio to pass thru - like 470K or 330K resistor once all the parts are reversed and try it that way?
You can even change the cap used, to a series of caps of various values - Electrolytic or not, some like 0.22uF or 0.1uf and even 1, 0.47uF - Tantalums give one effect, but Disc and Mylar another - mix and match to see if the caps can handle the various tones and their reactive elements adding and subtracting - versus tied to one value and it's particular character?
The method should work, the issues around "crappy" audio are due to filtering out spikes that are altering the audio waveform - the filter tries to fill in gaps but it cannot recreate missing information caused by the spikes overlay in the embedded audio. It limits it - trims it off but can't "insert data here" - your ears have to process the rest.
The removal or bypass, you can hear how well the radios receiver is, which for many is acceptable and nicely done. But we can't remove the line noise or other things the NB circuit has to take over and remove - again it punches holes in the signal and you're left with missing information.
So anyhoo...Hi How are you?
:+> Andy <+:
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