| Author |
Message |
    
Jose22
Member
Username: Jose22
Post Number: 70
Registered: 2-2002
| | Posted on Sunday, June 06, 2004 - 8:57 pm: | 
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I HAVE A GALAXY 959 AND 99V. BOTH SHOW GOOD SWING INTO DUMMY LOADS USING DOSEY AND OTHER METERS. RF METER ON BOTH LOOK GOOD. BUT.... I NOTICED AMPMETER ON POWER SUPPLY ACTUALLY DROPING WHEN MODULATION. I THOUGHT THIS WAS STRANGE. I THOUGH INCREASED MODULATION AND GREATER OUTPUT WOULD HAVE GREATER CURRENT DRAW. PLACED ON WAVETEC STABILOCK 4130 SERVICE MONITOR. I SHOWED WATTAGE ACTUALLY HIGHER ON DEAD KEY THAN OTHER METERS BUT DID SHOW WATTAGE DROP ON MODULATION. IS THIS SOMETHING TO DO WITH THE SERVICE MONITOR OR WHAT??
THANKS
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Tech8541
Moderator
Username: Tech8541
Post Number: 214
Registered: 12-2003
| | Posted on Monday, June 07, 2004 - 12:41 am: |
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both the service monitors wattmeter and the amp meter on the power supply are rms meters, not peak/pep meters.
to make a long story short, the backwards swing on the amp meter and wattage drop on the s.monitor means your deadkey is too high.
this is one reason it is good to use a 'true' rms meter. it will let you know if you do not have enough modulation/carrier set too high. the dosey and astatic meters will 'always' show some forward swing when you may still have negative modulation.
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Jose22
Member
Username: Jose22
Post Number: 71
Registered: 2-2002
| | Posted on Tuesday, June 08, 2004 - 8:53 pm: |
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Thanks, will reduce dead key via service monitor and let you know
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Tech8541
Moderator
Username: Tech8541
Post Number: 215
Registered: 12-2003
| | Posted on Wednesday, June 09, 2004 - 12:19 am: |
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if you want a s.monitor with a pep meter use the hp8920 or one of the ifr's. even then, unless you know what you are looking for, you may still have negative modulation. |
Tech548
Moderator
Username: Tech548
Post Number: 104
Registered: 5-2004
| | Posted on Wednesday, June 09, 2004 - 3:24 am: |
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Jose22
Remove R-264 and replace it with a 1N4001 diode making sure to place the banded end of the diode to the right. You may have to enlarge the holes a bit.
Set your deadkey to around 1.5 to 2 watts. With the lowered deadkey, you will still have the full swing capability and zero backswing on your amp meter.
There are other power modifications that can be done with this radio but lets see how this one works out for you.
As far as peak reading meters go, they will show you a forwards power swing whether you really have it or not. Try this little trick.
Put you Dosey meter in the SWR mode, key the mic and then roll the control knob up until the needle is around mid scale or anywhere under the "set" mark and then leave everything as is.
Send an audio signal or just say a long aauuuuhh into the mic while watching the meter. If the needle swings backwards, then you do indeed have downwards modulation. The deadkey is set way too high. This is the only was you can tell if you have a true forwards power swing on these meters.
Your Amperage meter on the power supply will tell the story also. If it goes backwards when the radio is modulated, that's a dead givaway that your output power is set too high. There just isn't enough room in that little final for high power and modulation too. Something HAS to give.
Try the above modification and then lower your deadkey. Loud and clean modulation rules---not RF power. You can't hear RF power! As you already know, it does nothing other than carry the modulation.
Jeff. |
Jose22
Member
Username: Jose22
Post Number: 72
Registered: 2-2002
| | Posted on Wednesday, June 09, 2004 - 8:22 pm: |
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Great advice Jeff. Will get in shack and try this weekend.
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Jose22
Member
Username: Jose22
Post Number: 73
Registered: 2-2002
| | Posted on Tuesday, June 15, 2004 - 8:50 pm: |
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NO JOY. tried mod and lowered dead key. results still no right. Too dead key down to 1.5 and got very little swing?? Must have something else wrong. Used the TX alignment instructions to adjust. Used VR to turn down power. Any other ideals??
Thanks
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Jose22
Member
Username: Jose22
Post Number: 74
Registered: 2-2002
| | Posted on Monday, June 21, 2004 - 6:47 pm: |
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Doing some research. Could this be with what is called the duty cycle??? As the modulation envelope increases the duty cycle decreases which causes the current draw to decrease.
Anyone???
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Dindin
Intermediate Member
Username: Dindin
Post Number: 201
Registered: 2-2004
| | Posted on Monday, June 21, 2004 - 9:26 pm: |
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dont think that is the term your after.duty cycle would be the percentage of on time compared to off time.as mod increases so does current draw.after mod passes 100% clipping starts.when an over driven final reaches saturation it starts shutting down resulting in the lower current draw,hence lower output.the function of the alc is to overcome the clipping and provide a more "level" signal to the next stage.Correct me if I'm wrong Tech's. |
Jose22
Member
Username: Jose22
Post Number: 75
Registered: 2-2002
| | Posted on Saturday, July 31, 2004 - 4:46 pm: |
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Ok guys. Have retuned TX and same results. Still searching. will try little longer and probably just accept.
Thanks |
Crackerjack
Intermediate Member
Username: Crackerjack
Post Number: 178
Registered: 7-2004
| | Posted on Saturday, July 31, 2004 - 6:15 pm: |
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How big is the power supply? |
Jose22
Member
Username: Jose22
Post Number: 76
Registered: 2-2002
| | Posted on Saturday, July 31, 2004 - 8:47 pm: |
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10 amp power supply..
Here is other info.
NO MODULATION:
DEAD KEY = Service Monitor ------ 9.68 watts
= Watt Meter ----------- 7.00 watts
= Current Draw ---------- 4.1 amps
Fully Modulated
= Service Monitor -------- 7.46 watts
= Watt Meter ----------- 20 watts
= Current Draw ----------- 3.5 amps
Service monitor is Stablilock 4130
Watt Meter is B & K 1040 test center (a stingy one)
Current Draw is amp meter on power supply.
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Tech548
Moderator
Username: Tech548
Post Number: 182
Registered: 5-2004
| | Posted on Saturday, July 31, 2004 - 11:44 pm: |
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Jose22
Let me get this straight.
You said that your Watt Meter shows a 7 watt deadkey with a 4.1 amperage draw??
And when fully modulated it shows you 20 watts with a 3.5 amperage draw??
How is this possible? Do you see where I'm going with this and why I'm questioning your results?
I bet Dindin does.
Jeff
Tech548 |
Jose22
Member
Username: Jose22
Post Number: 77
Registered: 2-2002
| | Posted on Sunday, August 01, 2004 - 9:12 pm: |
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548, you are correct. The watt meter is a b&k test station. the amp meter is part of the power supply. The service monitor show a output drop when fully modulated. I know it sounds crazy. but it is what i see. I will try and find my digital camera latter this week and take a short video if i can. Can it be added to a post? |
Dindin
Intermediate Member
Username: Dindin
Post Number: 301
Registered: 2-2004
| | Posted on Monday, August 02, 2004 - 8:36 pm: |
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Jose22,do you have access to an o-scope to see what is happing to your modulation as your power peaks?do not rely on a mod meteralso put an ammeter outboard of the p.s. to verify its reading |
Jose22
Member
Username: Jose22
Post Number: 78
Registered: 2-2002
| | Posted on Monday, August 02, 2004 - 9:04 pm: |
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I do have access to oscope and can put my ammeter in line. Know what to look for on ampmeter. Know what "standard" modulated carrier looks like. What should I look for on oscope?
Jose22 |
Dindin
Intermediate Member
Username: Dindin
Post Number: 304
Registered: 2-2004
| | Posted on Monday, August 02, 2004 - 11:31 pm: |
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Jose22,I'll try to post some sample traces showing normal ,over mod-clipping,and undermod tomorrow evening.way past my bedtime now. |
