I wonder if Lou Franklin copied channel guard from there or they did from Lou 
Mike
Mike
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Schottkey diode/transistor opinions
- Thread starter Hawkeye351
- Start date
Hawkeye, what you are experiencing is common with this and similar board designs.
The info im giving you came from a Galaxy factory tech many years ago.
the symptom is a very noisy receiver that will exhibit an S meter deflection even with no antenna connected.
the problem is the antenna coil, the one right before the Rf amp transistor.
in your radio this is L6.
the cure is to do the receiver alignment like normal, then unhook everything from the antenna jack on the radio.
radio on, RF gain at max, volume up. AM mode.
de-tune L6 just a bit and the noise will fall right off. it won't take much adjustment.
now you can check your work by putting the sig gen back into the radio so you can see how much sensitivity you lost. it won't be much at all, and once someone connects an antenna to the radio that brings in atmospheric noise, it won't matter at all.
give it a shot and let us know what you think.
LC
The info im giving you came from a Galaxy factory tech many years ago.
the symptom is a very noisy receiver that will exhibit an S meter deflection even with no antenna connected.
the problem is the antenna coil, the one right before the Rf amp transistor.
in your radio this is L6.
the cure is to do the receiver alignment like normal, then unhook everything from the antenna jack on the radio.
radio on, RF gain at max, volume up. AM mode.
de-tune L6 just a bit and the noise will fall right off. it won't take much adjustment.
now you can check your work by putting the sig gen back into the radio so you can see how much sensitivity you lost. it won't be much at all, and once someone connects an antenna to the radio that brings in atmospheric noise, it won't matter at all.
give it a shot and let us know what you think.
LC
Mike, what radio is that with the dual gate mosfet front end?
Brandon, dual gate mosfet front ends were the dream for many people about 20 years ago or so and there was a guy named Bill Good who designed a way to mod the 148gtl/2000gtl to use one.
I never saw one but apparently it worked very well. There's probably still a few out there in the wild.
also, there was a member here years ago that went by CBphreaker, and he made a mod for the AM detector that used an op amp. you can probably find it by searching through his old posts. i built one and it worked well but i ended up removing it from the radio at some point and i can't even remember why now lol.
you seem like someone who might find this interesting.
LC
Brandon, dual gate mosfet front ends were the dream for many people about 20 years ago or so and there was a guy named Bill Good who designed a way to mod the 148gtl/2000gtl to use one.
I never saw one but apparently it worked very well. There's probably still a few out there in the wild.
also, there was a member here years ago that went by CBphreaker, and he made a mod for the AM detector that used an op amp. you can probably find it by searching through his old posts. i built one and it worked well but i ended up removing it from the radio at some point and i can't even remember why now lol.
you seem like someone who might find this interesting.
LC
That schematic is from the DNT Traffic 1. The other DNT radios (at least the ones with a schematic on CBTricks) also used dual gate mosfets.
edit to remove pic. It's available on cbradio.nl, and radiomuseum.org has an internal pic too.
edit to remove pic. It's available on cbradio.nl, and radiomuseum.org has an internal pic too.
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Ok,
I been super busy but I found this very old thread, it is littered with bantering back and forth but contains some really deep digging into the 2n2999 / diode mods.
If you can stand digging through it to find the nuggets.
It started with how to do the mod them progressed
73
Jeff
Here is what I did just a couple hours ago while it's quiet on every band:
I realigned the radio by just the signal generator. Went through entire process.
Unhooked generator and moved all jumpers far away from the radios SO239 input (eliminate possibility of any stray signals from nearby coax).
Turned volume wide open.
Adjusted L6 for lowest noise level. Clockwise increased noise level all the way down, counter-clockwise showed a low dip before climbing again near the top (about 1.5 turns below top), so I set it for that lowest dip.
Turned volume down.
Hooked antenna back up.
Signal was 6 s-units on every channel, but I could barely hear my central heat/air unit anymore (which is a plus for me).
Instead of touching any receiver IFT adjustments, I adjusted VR1 and VR2 down to just a 1/4 of the way up on each.
I may stick with this for a few days, so far it seems to have at least eliminated a lot of my central heat/air units noise I used to get when it kicked in.
I'm still leaning on TR17 being weak or leaky. But for now I'll try this and get back with you all later on how well I like it like this.
I've been copying/pasting a lot of you all's conversations on this thread for future reference. A lot of very useful info I don't want to lose.
I still feel like I'm chasing ghosts, lol... I'll smoke some, that helps me focus more, lol....Wait, maybe smoking some is what's got me to chasing ghosts, lol...oh well I'll smoke some and think on that also, lol...
Thank you guys/gals...
I realigned the radio by just the signal generator. Went through entire process.
Unhooked generator and moved all jumpers far away from the radios SO239 input (eliminate possibility of any stray signals from nearby coax).
Turned volume wide open.
Adjusted L6 for lowest noise level. Clockwise increased noise level all the way down, counter-clockwise showed a low dip before climbing again near the top (about 1.5 turns below top), so I set it for that lowest dip.
Turned volume down.
Hooked antenna back up.
Signal was 6 s-units on every channel, but I could barely hear my central heat/air unit anymore (which is a plus for me).
Instead of touching any receiver IFT adjustments, I adjusted VR1 and VR2 down to just a 1/4 of the way up on each.
I may stick with this for a few days, so far it seems to have at least eliminated a lot of my central heat/air units noise I used to get when it kicked in.
I'm still leaning on TR17 being weak or leaky. But for now I'll try this and get back with you all later on how well I like it like this.
I've been copying/pasting a lot of you all's conversations on this thread for future reference. A lot of very useful info I don't want to lose.
I still feel like I'm chasing ghosts, lol... I'll smoke some, that helps me focus more, lol....Wait, maybe smoking some is what's got me to chasing ghosts, lol...oh well I'll smoke some and think on that also, lol...
Thank you guys/gals...
Wow, it can't be this simple, I feel like an idiot.
After using it like above for several hours, I'm impressed.
The signal reading on hash level shows about the same on any band/frequency or mode. One mode isn't higher than the other, no channel is higher than the other. The receive on all bands/frequencies and modes are almost equal.
Signals look right with audio, and the best part of all is my central heat/AC unit is coming in on my receive on any channel or mode.
Only difference from the alignment procedure in the service manual that I strayed from was the meter adjustments (VR1, VR2). I lowered those to just 1/4 turn up instead of the typical 1/2 way up.
Thanks guys, I thought I was stuck with that central heat/air noise.
After using it like above for several hours, I'm impressed.
The signal reading on hash level shows about the same on any band/frequency or mode. One mode isn't higher than the other, no channel is higher than the other. The receive on all bands/frequencies and modes are almost equal.
Signals look right with audio, and the best part of all is my central heat/AC unit is coming in on my receive on any channel or mode.
Only difference from the alignment procedure in the service manual that I strayed from was the meter adjustments (VR1, VR2). I lowered those to just 1/4 turn up instead of the typical 1/2 way up.
Thanks guys, I thought I was stuck with that central heat/air noise.
This sounds more like a bad thing than a good thing. Does the noise level drop when disconnecting the coax? If the noise is the same regardless of band or mode, I would assume the radio itself is the source of the noise, and disconnecting the coax and hearing no change would confirm that.
I've never had the same noise level when changing modes since the different filtering changes what outside noise is let through. Same should apply to changing bands on account of the different IF filter responses. Having everything equally noisy is a red flag IMO.
This is where having a -125dBm signal source comes in handy. That FY6800 signal generator you mentioned earlier does not go anywhere near that low. If you could string together about 90dB of attenuators, that sig gen would go low enough. I have almost the same one. The output voltage these sig gens show is pk-pk unloaded, and I know mine drops out at 2mVpk-pk, so if we assume the lowest setting we should use is 10mV pk-pk (thats unloaded, its half that into 50ohm), we get 3.5mV RMS or -36dBm into 50ohm at that setting. Adding 90dB of attenuation will get you in the -120's sufficient for weak signal alignment. 105dB of attenuation will give you more adjustment range though.
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Yes, if I unhook coax from the back of the radio then the signal and noise drops to nothing on signal and almost completely quiet (even with volume wide open), but when I hook coax back up, the signal meter comes up to what the noise level is and the audio comes up a lot.
Signals on locals looks about right, sounds great, even picking up signals lower than 2 s-units that I can actually hear now. SSB receive is beautiful and meter corresponds to audio. Best part is, no more central heat/air unit noise but receive is great, better this way.
Signals on locals looks about right, sounds great, even picking up signals lower than 2 s-units that I can actually hear now. SSB receive is beautiful and meter corresponds to audio. Best part is, no more central heat/air unit noise but receive is great, better this way.