Hi Guys,
Years ago my brother was into freebanding and had a really nice setup, a full Yaesu FT-101E station. As a young teenager I had a lot of fun talking DX with it and later I did get a ham ticket and put that equipment to full use.
As time went on, I went to college, got married, etc. and I got away from radio and my brother sold his setup years ago.
Recently I've had some renewed interest though and thought I may give a look at freebanding, or possibly getting a ham ticket again.
I found a good deal on a used Galaxy 979 CB and matching FC-347 frequency counter, I liked it because it can freeband and be converted to 10 meter use if I go that way.
There seems to be basically one mod method for the 979 and I'm curious type, I don't like to just follow the directions, I like to understand what it is I'm actually doing and the instructions for the 979 channel mod are a bit perplexing to me and I was wondering if someone could help clear things up for me?
Some of this could be found by experimentation, but my radio isn't here yet so I'm just looking at the schematics and board prints right now.
My understanding of how the frequency selection works is:
The 40 position channel switch has 7 output lines, each of these output lines can either be set high (designated by a 1) or low (designated by a 0).
The RCI8719 PLL chip is controlled by those 7 lines coming from the channel selector, what frequency the radio operates on is controlled by how those lines are set.
For instance, the channel selector output lines are designated as P6, P5, P4, P3, P2, P1 and P0 and they connect to the PLL chip on pins 10, 11, 12, 13, 14, 15 and 16. By having them set as 1100000 channel 15 is generated.
By overriding the inputs from the channel selector we can set the PLL control lines to create channels other than those normally allocated. The override is done by installing switches and tying their contacts to the PLL power leg or to the board ground and the PLL input line we wish to override and force to a certain state.
For instance, the channel selector is set to channel 15 as per the previous example which sets the control lines to 1100000, if we would connect P6 (pin 10) to ground then the power being fed to pin 10 via the channel switch to set it high would be shunted to ground and the lines would be set as 0100000 which would generate channel 77 (27.775). If we would also ground P5 (pin 11) at the same time then the lines would be set to 0000000, which would generate channel 45 (27.445).
In another example, if the channel selector was set to channel 12 then the lines would be set as 1011101. If we would connect P5 (pin 11) to power we would force it high and the lines would be set as 1111101 which would generate channel 42 (27.425). From what I gather, if the line is set as low by the channel selector power is simply not fed to it, but it's not connected to ground so it won't shunt the power we are injecting to ground, the line will simply go high.
My understanding is that we can force any channel within the design parameters to be created by simply setting those 7 lines correctly.
With the above in mind, the channel expansion method posted on several internet sites pretty much makes sense - the channel selector is set to a certain channel and then control lines are grounded or powered as required to modify the control settings for that channel to generate the new channel, the only part that doesn't seem to make any sense to me is where a couple resistors come into the equation.
The channel expansion method that seems to be the only one around is in a gif attached to this message.
I don't understand what part the 4.7K resistors play.
Doing a little research I found that in digital circuits leaving a line unpowered may result in the line picking up noise and it's value floating rather than remaining at what is considered the false, or zero, level. To combat this floating pull up or pull down resistors can be used. From what I gather, pull up resistors are normally ran from constant power through a fairly high value resistor to the line to keep a comparatively low constant level on the line. Pull down resistors are usually placed between the line and ground to help sink any stray noise. Two different ways to do the same thing.
The modification instructions say because this PLL chip doesn't have internal pull up resistors we have to provide one by soldering it across the pc trace we cut. Looking at the schematic, it appears to me that this circuit is using pull down resistors (and capacitors, probably to help suppress spikes?), they are R327 (P6), R326 (P5), R325 (P4), R324 (P3), R323 (P2), R322 (P1) and R321 (P0) and they are on the traces between where the lines come in from the channel selector on J33 and where they connect to the PLL pins. If one cuts the traces where instructed to, they are still in the circuit and should still be functional.
Cutting the traces where instructed simply disconnects the line from the channel selector.
I've attached a gif of the mod that shows where the suspected pull down resistors are at.
In normal operation, P6 (pin 10) is always high so the P6 line from the channel selector would always be powered so running a resistor to it could provide the pull up function, however P5 (pin 11) is low from channel 1 to channel 14, so it wouldn't always have power and thus it wouldn't be able to provide the pull up function all the time. But again, I don't think this circuit uses pull ups, I think it uses pull downs.
While we're discussing the cut traces, I don't like to cut traces. It's just a pain as they're always in cramped quarters it seems, and you have to scrape the lacquer off to get a good solder joint and stuff. It's just not a job I enjoy doing. In this case, the trace we are cutting is fed by a wiring harness from the channel selector though J33, I would think it would be preferable to simply cut the wiring harness to install the resistors and switches. Even if you needed to use the resistors just solder them in series and the switch connections below them, then no cutting or soldering on the board at all.
Also, one of the complaints about the channel mod for these units is that there is no modification bypass so you can tune through the normal 40 channels just like an unmodified radio. The mod for the Galaxy 959, which also uses the RCI8719 PLL chip and also seems to use pull down resistors (they are in a resistor network rather than separate ones like on the 979), simply puts single pole single throw switches in line with the P5 and P6 channel selector wire harness feed to the board, opening these switches puts P6 and P5 low (well, floating low, not forced low with a ground connection). I'm wondering if a similar mod wouldn't work for this radio? You wouldn't get as many channels, but you would get most of the upper channels.
I'm wondering if you used a double pole, double throw, center off switch and hooked PLL pins 10 and 11 to the top two poles, then the wiring harness P6 and P5 feeds to the center two poles and then didn't connect PLL pin 10 to the bottom pole, but did connect PLL pin 11 to the corresponding bottom pole if it wouldn't work? I don't know if pin 10 in this circuit responds to just floating low as opposed to being connected to ground, but the 959 uses a similar circuit and it seems to work. (One note here - doing some research it seems there are two versions of the RCI8719 PLL chips, the -97 version and the -99 version. The -97 has pin 10 tied high internally so it can't be forced low, the -99 is not tied high interanlly and can be forced low. One mod page I read noted the -99 needs a pull down resistor and suggested using a 10K resistor connected from pin 10 to ground, but again - I think there already is a pull down resistor in the circuit, R327, though I don't know it's value as I don't have my radio yet and it's not listed in the service manual.)
.....ic pin 10 11
chan sel P6 P5
.....ic pin --- 11
In the top position the lines would be connected as normal and the radio would operate as normal, in the center position both pins 10 and 11 would be disconnected, i.e. they'd be low. In the lower position pin 10 would not be connected but pin 11 would be.
I think this would give:
Switch in upper position: normal operation
Switch in the center position: 27.455 to 27.765 on channels 15 through 40 with the normal skips due to the A channels.
Switch in the down position: 27.775 to 28.045 on channels 15 through 40 with the normal skips due to the A channels.
Anyway, this is my first post and it's a long one, sorry about that! I can't wait to get my radio and do a little playing, before then though I'd like to line the modifications up I want to do and I'd like to understand what I'm doing, so if anyone could shed any light on the subject I'd sincerely appreciate it!
Thanks,
Steve
Years ago my brother was into freebanding and had a really nice setup, a full Yaesu FT-101E station. As a young teenager I had a lot of fun talking DX with it and later I did get a ham ticket and put that equipment to full use.
As time went on, I went to college, got married, etc. and I got away from radio and my brother sold his setup years ago.
Recently I've had some renewed interest though and thought I may give a look at freebanding, or possibly getting a ham ticket again.
I found a good deal on a used Galaxy 979 CB and matching FC-347 frequency counter, I liked it because it can freeband and be converted to 10 meter use if I go that way.
There seems to be basically one mod method for the 979 and I'm curious type, I don't like to just follow the directions, I like to understand what it is I'm actually doing and the instructions for the 979 channel mod are a bit perplexing to me and I was wondering if someone could help clear things up for me?
Some of this could be found by experimentation, but my radio isn't here yet so I'm just looking at the schematics and board prints right now.
My understanding of how the frequency selection works is:
The 40 position channel switch has 7 output lines, each of these output lines can either be set high (designated by a 1) or low (designated by a 0).
The RCI8719 PLL chip is controlled by those 7 lines coming from the channel selector, what frequency the radio operates on is controlled by how those lines are set.
For instance, the channel selector output lines are designated as P6, P5, P4, P3, P2, P1 and P0 and they connect to the PLL chip on pins 10, 11, 12, 13, 14, 15 and 16. By having them set as 1100000 channel 15 is generated.
By overriding the inputs from the channel selector we can set the PLL control lines to create channels other than those normally allocated. The override is done by installing switches and tying their contacts to the PLL power leg or to the board ground and the PLL input line we wish to override and force to a certain state.
For instance, the channel selector is set to channel 15 as per the previous example which sets the control lines to 1100000, if we would connect P6 (pin 10) to ground then the power being fed to pin 10 via the channel switch to set it high would be shunted to ground and the lines would be set as 0100000 which would generate channel 77 (27.775). If we would also ground P5 (pin 11) at the same time then the lines would be set to 0000000, which would generate channel 45 (27.445).
In another example, if the channel selector was set to channel 12 then the lines would be set as 1011101. If we would connect P5 (pin 11) to power we would force it high and the lines would be set as 1111101 which would generate channel 42 (27.425). From what I gather, if the line is set as low by the channel selector power is simply not fed to it, but it's not connected to ground so it won't shunt the power we are injecting to ground, the line will simply go high.
My understanding is that we can force any channel within the design parameters to be created by simply setting those 7 lines correctly.
With the above in mind, the channel expansion method posted on several internet sites pretty much makes sense - the channel selector is set to a certain channel and then control lines are grounded or powered as required to modify the control settings for that channel to generate the new channel, the only part that doesn't seem to make any sense to me is where a couple resistors come into the equation.
The channel expansion method that seems to be the only one around is in a gif attached to this message.
I don't understand what part the 4.7K resistors play.
Doing a little research I found that in digital circuits leaving a line unpowered may result in the line picking up noise and it's value floating rather than remaining at what is considered the false, or zero, level. To combat this floating pull up or pull down resistors can be used. From what I gather, pull up resistors are normally ran from constant power through a fairly high value resistor to the line to keep a comparatively low constant level on the line. Pull down resistors are usually placed between the line and ground to help sink any stray noise. Two different ways to do the same thing.
The modification instructions say because this PLL chip doesn't have internal pull up resistors we have to provide one by soldering it across the pc trace we cut. Looking at the schematic, it appears to me that this circuit is using pull down resistors (and capacitors, probably to help suppress spikes?), they are R327 (P6), R326 (P5), R325 (P4), R324 (P3), R323 (P2), R322 (P1) and R321 (P0) and they are on the traces between where the lines come in from the channel selector on J33 and where they connect to the PLL pins. If one cuts the traces where instructed to, they are still in the circuit and should still be functional.
Cutting the traces where instructed simply disconnects the line from the channel selector.
I've attached a gif of the mod that shows where the suspected pull down resistors are at.
In normal operation, P6 (pin 10) is always high so the P6 line from the channel selector would always be powered so running a resistor to it could provide the pull up function, however P5 (pin 11) is low from channel 1 to channel 14, so it wouldn't always have power and thus it wouldn't be able to provide the pull up function all the time. But again, I don't think this circuit uses pull ups, I think it uses pull downs.
While we're discussing the cut traces, I don't like to cut traces. It's just a pain as they're always in cramped quarters it seems, and you have to scrape the lacquer off to get a good solder joint and stuff. It's just not a job I enjoy doing. In this case, the trace we are cutting is fed by a wiring harness from the channel selector though J33, I would think it would be preferable to simply cut the wiring harness to install the resistors and switches. Even if you needed to use the resistors just solder them in series and the switch connections below them, then no cutting or soldering on the board at all.
Also, one of the complaints about the channel mod for these units is that there is no modification bypass so you can tune through the normal 40 channels just like an unmodified radio. The mod for the Galaxy 959, which also uses the RCI8719 PLL chip and also seems to use pull down resistors (they are in a resistor network rather than separate ones like on the 979), simply puts single pole single throw switches in line with the P5 and P6 channel selector wire harness feed to the board, opening these switches puts P6 and P5 low (well, floating low, not forced low with a ground connection). I'm wondering if a similar mod wouldn't work for this radio? You wouldn't get as many channels, but you would get most of the upper channels.
I'm wondering if you used a double pole, double throw, center off switch and hooked PLL pins 10 and 11 to the top two poles, then the wiring harness P6 and P5 feeds to the center two poles and then didn't connect PLL pin 10 to the bottom pole, but did connect PLL pin 11 to the corresponding bottom pole if it wouldn't work? I don't know if pin 10 in this circuit responds to just floating low as opposed to being connected to ground, but the 959 uses a similar circuit and it seems to work. (One note here - doing some research it seems there are two versions of the RCI8719 PLL chips, the -97 version and the -99 version. The -97 has pin 10 tied high internally so it can't be forced low, the -99 is not tied high interanlly and can be forced low. One mod page I read noted the -99 needs a pull down resistor and suggested using a 10K resistor connected from pin 10 to ground, but again - I think there already is a pull down resistor in the circuit, R327, though I don't know it's value as I don't have my radio yet and it's not listed in the service manual.)
.....ic pin 10 11
chan sel P6 P5
.....ic pin --- 11
In the top position the lines would be connected as normal and the radio would operate as normal, in the center position both pins 10 and 11 would be disconnected, i.e. they'd be low. In the lower position pin 10 would not be connected but pin 11 would be.
I think this would give:
Switch in upper position: normal operation
Switch in the center position: 27.455 to 27.765 on channels 15 through 40 with the normal skips due to the A channels.
Switch in the down position: 27.775 to 28.045 on channels 15 through 40 with the normal skips due to the A channels.
Anyway, this is my first post and it's a long one, sorry about that! I can't wait to get my radio and do a little playing, before then though I'd like to line the modifications up I want to do and I'd like to understand what I'm doing, so if anyone could shed any light on the subject I'd sincerely appreciate it!
Thanks,
Steve
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