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Not sure what the mod is called to broadcast on multiple channels...
- Thread starter mattsowders1989
- Start date
To learn about the various modifications that have been installed in radios over the years. It is quite interesting to me actually, even though I will probably never install this mod.
Resurrecting an old thread. Found this mod in an old GE A model we bought at a yard sale.
GE was rusted out dead beyond repair it had been in a wet garage for decades.
But built a new circuit as above and put it in a working cybernet base radio.
And it works real good, put radio on channel 32 and it transmits on every channel from 23 to 40 at the same time. Never had so much fun with a dollars worth of parts.
Local ham wanted to know how the heck I did it. Told him I pulled the channel knob off and attached a power drill to the shaft and pulled the trigger. The funny thing was I think he believed me LOL
Not sure of how such a simple circuit works, i'm an electrician and radio tinkerer but no technician. Will forward this thread to our tech for an explanation if no-one can tell me how it does what it does.
Its not a fully wideband transmission though. Listening on a ham rig with a vfo and tuning up and down shows that the duplicated channels are only every 10K, i.e. you cant hear the transmission on 27.360 but you can on 27.355 and 27.365 megs.
The mod also works on reception. Put radio on channel 32 and you can hear conversations on every channel from 23 to 40 at the same time. But nothing is received when the ham radio rig transmits on a zero frequency such as 27.360 megs. Strange.
Thanks to Kev who scanned and cleaned to the picture above.
Any explanation how this thing works without getting too technical?
Loz!
GE was rusted out dead beyond repair it had been in a wet garage for decades.
But built a new circuit as above and put it in a working cybernet base radio.
And it works real good, put radio on channel 32 and it transmits on every channel from 23 to 40 at the same time. Never had so much fun with a dollars worth of parts.
Local ham wanted to know how the heck I did it. Told him I pulled the channel knob off and attached a power drill to the shaft and pulled the trigger. The funny thing was I think he believed me LOL
Not sure of how such a simple circuit works, i'm an electrician and radio tinkerer but no technician. Will forward this thread to our tech for an explanation if no-one can tell me how it does what it does.
Its not a fully wideband transmission though. Listening on a ham rig with a vfo and tuning up and down shows that the duplicated channels are only every 10K, i.e. you cant hear the transmission on 27.360 but you can on 27.355 and 27.365 megs.
The mod also works on reception. Put radio on channel 32 and you can hear conversations on every channel from 23 to 40 at the same time. But nothing is received when the ham radio rig transmits on a zero frequency such as 27.360 megs. Strange.
Thanks to Kev who scanned and cleaned to the picture above.
Any explanation how this thing works without getting too technical?
Loz!
This is a different way to do it. We use a 10.24 MHz crystal, a chip to divide that down to 10 kHz, and a relay connected to the radio's transmit line. Keeps you from receiving 40 channels at once.
How it works has to do with the radio's Voltage Controlled Oscillator, or VCO. The PLL chip in the radio feeds the exact DC voltage needed to tune in the channel you have selected. Never mind how it does this, Just think of a variable-frequency knob with a guy holding it in one hand, with a frequency counter in his direct view. When the frequency on the counter drifts up, he turns the knob to bring it back down on channel. If it drifts up, he turns the knob the other way.
Technically, this would be called a "human frequency-locked loop". The term "Phase Locked Loop" just means that the circuits in the radio's PLL chip are a lot faster than the the guy with the VFO knob. The frequency is corrected from any drift 10,000 times a second.
The radio's VCO can be used as a FM modulator. Just put audio voltage onto the DC tuning voltage it already uses.
If you put a square wave onto that tuning voltage, the FM signal you now get will look like an army of "cloned" AM signals, just like the one the radio gives you in the first place. But each of those individual AM 'copies' of your signal will be spaced apart at the frequency of your square wave.
If you use a 10 kHz square wave like the circuit above, you get a bunch of "clones", copies of your AM signal on every 10 kHz channel above and below the channel on the radio's selector.
How many of them? This is determined by the modulation level of the 10 kHz square wave. This trick can give the PLL in some radios a headache, and cause it to trip the "Out of Lock" detector. That circuit serves to disable the radio's transmitter when the PLL loses control of your (legal) transmit frequency. It will typically take a 2-Volt or 3-Volt peak-to-peak square wave to produce around 40 cloned signals, 20 above and 20 below your center channel.
But not all PLL circuits are created equal.
Your mileage may vary.
73
How it works has to do with the radio's Voltage Controlled Oscillator, or VCO. The PLL chip in the radio feeds the exact DC voltage needed to tune in the channel you have selected. Never mind how it does this, Just think of a variable-frequency knob with a guy holding it in one hand, with a frequency counter in his direct view. When the frequency on the counter drifts up, he turns the knob to bring it back down on channel. If it drifts up, he turns the knob the other way.
Technically, this would be called a "human frequency-locked loop". The term "Phase Locked Loop" just means that the circuits in the radio's PLL chip are a lot faster than the the guy with the VFO knob. The frequency is corrected from any drift 10,000 times a second.
The radio's VCO can be used as a FM modulator. Just put audio voltage onto the DC tuning voltage it already uses.
If you put a square wave onto that tuning voltage, the FM signal you now get will look like an army of "cloned" AM signals, just like the one the radio gives you in the first place. But each of those individual AM 'copies' of your signal will be spaced apart at the frequency of your square wave.
If you use a 10 kHz square wave like the circuit above, you get a bunch of "clones", copies of your AM signal on every 10 kHz channel above and below the channel on the radio's selector.
How many of them? This is determined by the modulation level of the 10 kHz square wave. This trick can give the PLL in some radios a headache, and cause it to trip the "Out of Lock" detector. That circuit serves to disable the radio's transmitter when the PLL loses control of your (legal) transmit frequency. It will typically take a 2-Volt or 3-Volt peak-to-peak square wave to produce around 40 cloned signals, 20 above and 20 below your center channel.
But not all PLL circuits are created equal.
Your mileage may vary.
73
So if I read that right you're basically transmitting a single 40 channel wide FM signal with "audio" that just happens to look like 40 individual AM signals 10 kHz apart to the receiving station? if so that's quite a clever trick.
If as hpssb says it also works on the recieve end a radio modified like this would be quite useful to DXers as a conditions monitor of sorts, you may not be able to pick out any coherent signals from the mess in its receive but it will alert you to the fact that signals are there somewhere on the band.
If as hpssb says it also works on the recieve end a radio modified like this would be quite useful to DXers as a conditions monitor of sorts, you may not be able to pick out any coherent signals from the mess in its receive but it will alert you to the fact that signals are there somewhere on the band.
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No, it's really all about sidebands.
FM sidebands. They're different from AM sidebands.
I need to post a YT vid of the spectrum display while this thing is transmitting.
Key the stock AM radio and you see one peak on the display, at the carrier frequency. Modulate it and you see energy just above and below the carrier's frequency. Those are the AM sidebands that carry the voice modulation.
Turn on the "clone army" switch and now you see copies of that AM signal, all spaced exactly 10 kHz apart, above and below the channel frequency. Each of these sounds just like the original signal on the original channel.
A square wave at 10 kHz produces two or more FM sidebands, one below and one above the center frequency. Each one is basically a copy of the original AM signal. The frequency of the square wave sets how far away the FM sidebands will spread out from the center frequency. The higher the level of the square wave feeding into the VCO, the farther away from the center channel these 'clone' signal pop up, each spaced exactly one channel apart.
But the law of conservation of energy still applies. A 4-Watt signal spread across 40 channels only has about 1/10 of a Watt per channel. The wattmeter won't show a difference, but you can't get something for nothing. More channels means less power per channel.
73
FM sidebands. They're different from AM sidebands.
I need to post a YT vid of the spectrum display while this thing is transmitting.
Key the stock AM radio and you see one peak on the display, at the carrier frequency. Modulate it and you see energy just above and below the carrier's frequency. Those are the AM sidebands that carry the voice modulation.
Turn on the "clone army" switch and now you see copies of that AM signal, all spaced exactly 10 kHz apart, above and below the channel frequency. Each of these sounds just like the original signal on the original channel.
A square wave at 10 kHz produces two or more FM sidebands, one below and one above the center frequency. Each one is basically a copy of the original AM signal. The frequency of the square wave sets how far away the FM sidebands will spread out from the center frequency. The higher the level of the square wave feeding into the VCO, the farther away from the center channel these 'clone' signal pop up, each spaced exactly one channel apart.
But the law of conservation of energy still applies. A 4-Watt signal spread across 40 channels only has about 1/10 of a Watt per channel. The wattmeter won't show a difference, but you can't get something for nothing. More channels means less power per channel.
73
The mod in the sheet I posted earlier does about 15 channels, so that means each one is just under a watt (we are talking SSB here, AM is not used on 27 megs in Oz). Put it through a KLB-240 200 watt amp which in theory would have bought each of the sidebands back up close to the original 12 watts the radio does barefoot on one channel.
And on Saturday evening the skip was running
Was getting the east cost 20+/9 with just a hygain 5/8 penetrator antenna. Wideband switch and amp on + a few beers = instant radio havoc. Haven't heard reactions like we got since the 27 meg heyday of the 80's.
Thanks for the explanation although most of it went over my head.
One question - is that circuit adaptable to the Cobra 148 (side mic Malaysia made) or the Cobra 2000 (the base radio with the frequency counter) radios?
And on Saturday evening the skip was running
Was getting the east cost 20+/9 with just a hygain 5/8 penetrator antenna. Wideband switch and amp on + a few beers = instant radio havoc. Haven't heard reactions like we got since the 27 meg heyday of the 80's.
Thanks for the explanation although most of it went over my head.
One question - is that circuit adaptable to the Cobra 148 (side mic Malaysia made) or the Cobra 2000 (the base radio with the frequency counter) radios?
Umm, "the circuit", as in the one show above?
Don't know. Never tried it. Looks simple and cute, but that's about all I know about it. Shows only a hookup for PLL02A pll chips. What it will do with a MB8719 I have no idea. Might not work at all.
I have found that what works best is a connection directly to the 'hot' side of the VCO's varactor diode. Feeding the 10 kHz square wave to it through 56k resistor will isolate the VCO from being loaded down by the 10 kHz source.
Radios that use an epoxy-coated "plate" VCO module like the Uniden-made 40-channel SSB CB models do not adapt to this as easily. The varactor diode is under that layer of shiny coating, and you can't connect directly to it. Found that if you cut the foil trace to the plate's tuning-voltage pin you can connect a 10k resistor across the cut. This allows the PLL to function normally. You'll feed the square wave to the tuning-voltage pin of the VCO plate, through a proper isolation resistor as you do for the Cobra 29 radios. But this won't get you quite the range of channels that the direct-to-varactor setup does.
And later RCI-made boards like the EPT6900 series, or EPT696 use a similar VCO module, but the parts are exposed, not covered in epoxy.
General rule has been that simpler AM-only radios will do this trick better than SSB models. Works best by hooking directly to the varactor diode. If that diode is inside a module, the performance will tend to be reduced.
This is still a custom modification. Every radio design that's different will affect what you have to do to that particular radio type, and how it will perform, both.
73
Don't know. Never tried it. Looks simple and cute, but that's about all I know about it. Shows only a hookup for PLL02A pll chips. What it will do with a MB8719 I have no idea. Might not work at all.
I have found that what works best is a connection directly to the 'hot' side of the VCO's varactor diode. Feeding the 10 kHz square wave to it through 56k resistor will isolate the VCO from being loaded down by the 10 kHz source.
Radios that use an epoxy-coated "plate" VCO module like the Uniden-made 40-channel SSB CB models do not adapt to this as easily. The varactor diode is under that layer of shiny coating, and you can't connect directly to it. Found that if you cut the foil trace to the plate's tuning-voltage pin you can connect a 10k resistor across the cut. This allows the PLL to function normally. You'll feed the square wave to the tuning-voltage pin of the VCO plate, through a proper isolation resistor as you do for the Cobra 29 radios. But this won't get you quite the range of channels that the direct-to-varactor setup does.
And later RCI-made boards like the EPT6900 series, or EPT696 use a similar VCO module, but the parts are exposed, not covered in epoxy.
General rule has been that simpler AM-only radios will do this trick better than SSB models. Works best by hooking directly to the varactor diode. If that diode is inside a module, the performance will tend to be reduced.
This is still a custom modification. Every radio design that's different will affect what you have to do to that particular radio type, and how it will perform, both.
73
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Tried it on another PLL02A Cybernet, this time a mobile. Worked almost the same, covers about 15 channels with good signal strength before dropping away quickly beyond that. Will try it on a Cobra 148 when we get one. Any idea what the equivalent of PLL02A pin 6 is on the MB8734 chip used in the Cobras is?
Loz!
Loz!
Pin 6 on the PLL02A is the lock-detect output. Wouldn't have thought to use that one.
Strangely enough, pin 6 is also the lock detector for the 8719 and 8734, both.
Not what I expected. Now I'm trying to figure out just what makes it work. Makes it tough to predict whether or not the 8719 will behave like a PLL02A with the same setup. Gotta figure this one out. Our method is more straightforward and doesn't 'borrow' any signals from the radio's PLL chip, just generates the 10 kHz from its own 10.24 crystal.
Biggest issue you'll see with a radio that uses the 8719/34 will be to feed your chip's output into the VCO's tuning voltage. The trick I described above for the "plate" VCO module found in Uniden radios that use the 8719 may be necessary to get any coverage.
73
Strangely enough, pin 6 is also the lock detector for the 8719 and 8734, both.
Not what I expected. Now I'm trying to figure out just what makes it work. Makes it tough to predict whether or not the 8719 will behave like a PLL02A with the same setup. Gotta figure this one out. Our method is more straightforward and doesn't 'borrow' any signals from the radio's PLL chip, just generates the 10 kHz from its own 10.24 crystal.
Biggest issue you'll see with a radio that uses the 8719/34 will be to feed your chip's output into the VCO's tuning voltage. The trick I described above for the "plate" VCO module found in Uniden radios that use the 8719 may be necessary to get any coverage.
73