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Galaxy 99V Bad sounding SSB
- Thread starter Low_Boy
- Start date
Ok, there is much to be considered when RF induction or interference is suspected as the possible issue. First RF can cause voltage fluctuations in sensitive circuits like Carrier offset oscillators and PLL offset oscillators which both can cause what sounds like warble or underwater audio which is almost a sure bet that its frequency is shifting up or down from its baseline or whatever the clarifier is set to at the moment. This RF can be rectified in these circuits causing very small changes in the varactors such as D124. On radios like Galaxies, there is always the issue of harmonics which can expand the problem and be the reason as well but not always the only reason. This is why it may be advantageous to remove the driver and final from the equation and if by some chance you can hear in the monitor a significant change then you may have found the beginning of a cure.
Ok, Remove the bus bar copper plate in the final section and try talking into the monitor radio try using a small length of wire in the monitor radio just long enough to get a signal into the monitor radio if you must but you find you don't have to do that. You may want to also consider using headphones. try this method with a radio you know is working good on SSB so you can get a feel for what works best you will find this to be a good way to listen to problem radios when you figure out the right method.
"I hereby reserve the right to revise and extend my remarks" OldTech
OldTech. I did pull the bias bar and try talking into my test radio and really could not hear much of a difference with or without the bar in. I really do not think it sounds bad all that bad on my test radio but the people on the other end seem to notice it. I have a old Palamar SWR Power meter that has a head phone jack it says for monitoring AM maybe I will see if it works on SSB.
look at the bottom of the board and make sure all the parts are in place and have not been removed. even verify the 2 shields are in place. some one may have been in there before you and removed some parts off the bottom of the board.
http://www.cbtricks.com/radios/galaxy/dx99v/graphics/99v_3600-14b_bot_color.gif
http://www.cbtricks.com/radios/galaxy/dx99v/graphics/99v_3600-14b_bot_color.gif
The vast bulk of SSB audio-quality trouble I see on transmit boils down to two errors.
1) Bias set too low on driver or finals.
2) Missing TR32, removed to improve the AM modulated power level. You'll have to put back TR32 to run sideband without having to "play" the mike gain like a violin.
Next-most common would be to find the ALC trimpot VR12 and see if it's just set too high. SSB is different from AM. Setting the SSB limiter (ALC) too high doesn't make it louder like AM. Just makes it nasty.
Quick way to settle the "bias" versus "limiter" question is to listen on a second radio, and turn the mike gain down. Set it for about 1 or 2 Watts of sideband swing. If this makes it sound worse, you have a bias problem.
If this makes it sound really good, that means the bias is okay, and the distortion is more likely a disabled limiter, or VR12 just set too high.
Of course, if the radio has BOTH one or more wrong bias settings AND the limiter is disabled, this test won't reveal a lot.
Setting VR12 without a 'scope can be done. Crank the mike gain and set the wattmeter for average power. Set VR12 for max modulated power, then turn it slowly back the other way. There will be a drastic "kick-in" point where the wattmeter falls like a rock. Good chance that this setting will be close to correct. A peak meter will show that you didn't turn it down too far.
73
1) Bias set too low on driver or finals.
2) Missing TR32, removed to improve the AM modulated power level. You'll have to put back TR32 to run sideband without having to "play" the mike gain like a violin.
Next-most common would be to find the ALC trimpot VR12 and see if it's just set too high. SSB is different from AM. Setting the SSB limiter (ALC) too high doesn't make it louder like AM. Just makes it nasty.
Quick way to settle the "bias" versus "limiter" question is to listen on a second radio, and turn the mike gain down. Set it for about 1 or 2 Watts of sideband swing. If this makes it sound worse, you have a bias problem.
If this makes it sound really good, that means the bias is okay, and the distortion is more likely a disabled limiter, or VR12 just set too high.
Of course, if the radio has BOTH one or more wrong bias settings AND the limiter is disabled, this test won't reveal a lot.
Setting VR12 without a 'scope can be done. Crank the mike gain and set the wattmeter for average power. Set VR12 for max modulated power, then turn it slowly back the other way. There will be a drastic "kick-in" point where the wattmeter falls like a rock. Good chance that this setting will be close to correct. A peak meter will show that you didn't turn it down too far.
73
I agree with Nomad here. "Warbling" on SSB is commonly caused be improper driver/final bias.
As an aside ... the carrier suppression adjustment on Galaxy SSB rigs is touchy, and it's hard to find the "sweet spot" where there is no carrier on either sideband. What I've been doing is to remove the suppression adjustment pot (VR7 in this case) and replace it with a 10-turn PC pot. The 10 turns of adjustment makes it very easy to get the suppression spot-on.
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As an aside ... the carrier suppression adjustment on Galaxy SSB rigs is touchy, and it's hard to find the "sweet spot" where there is no carrier on either sideband. What I've been doing is to remove the suppression adjustment pot (VR7 in this case) and replace it with a 10-turn PC pot. The 10 turns of adjustment makes it very easy to get the suppression spot-on.
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I suspect 2 things.
1. Voltage fluctation on varactor diode D124 on TX. You won't hear that on AM.
2. Deffective IC8 or (and) IC10
Mike
1. Voltage fluctation on varactor diode D124 on TX. You won't hear that on AM.
2. Deffective IC8 or (and) IC10
Mike
Lets see.
I did try talking and lowering the ALC while talking and was told the radio sounded the same but the volume/modulation was lower.
I never tried playing with the final and driver bias except for setting bias at driver 50ma 1st final 50ma and 2nd final 100ma. Then retested everything when the radio still sounded bad. All was correct.
Mike.. I have not checked the voltage on the varactor diode Or IC8 or IC10. I am not sure how I would check voltage to the varactor diode I can check the pins on IC8 and IC10 and see if all shows correct.
Nomad I will try your test and see if I can tell a difference.
I did try talking and lowering the ALC while talking and was told the radio sounded the same but the volume/modulation was lower.
I never tried playing with the final and driver bias except for setting bias at driver 50ma 1st final 50ma and 2nd final 100ma. Then retested everything when the radio still sounded bad. All was correct.
Mike.. I have not checked the voltage on the varactor diode Or IC8 or IC10. I am not sure how I would check voltage to the varactor diode I can check the pins on IC8 and IC10 and see if all shows correct.
Nomad I will try your test and see if I can tell a difference.
well i'm still guessing here, but i'd like to know what the collector of TR41 does on SSB modulated TX.
It should sit steady at about 8.5 volts. does it sag under modulation on SSB?
you also might want to look around the area of TR32 and make sure that someone didn't do something stupid like removing a diode in that area or something.
LC
It should sit steady at about 8.5 volts. does it sag under modulation on SSB?
you also might want to look around the area of TR32 and make sure that someone didn't do something stupid like removing a diode in that area or something.
LC
I will be back on this tomorrow. I got involved in something that was supposed to just be a quick little thing that turned out to be a big mess. I will post my findings on the 99V tomorrow.
Sonoma.... you might have something here I just pulled that radio over to the bench to start checking voltages on the ver actor diode and TR 41 and there is one Shield missing it doesn't look like it was ever on the radio I'm comparing it with another Galaxy 99 it is The Shield that goes over the surface mount ver actor diode. I don't even see any solder Globs on the board where there ever was a shield.
Correction it goes just under the veractor diode on the bottom side of the board.
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Yes the upper shield is missing. Also there are 2 Varactor diodes D94 and D30. So far I checked TR 41 collector and 8.83V and it goes up to 8.98V with modulation so that Is good. If I don't keep getting distracted I will post my varactor diode findings in a little while.
Edit I forgot D124 Sorry OldTech.
Edit I forgot D124 Sorry OldTech.
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