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Message |
    
Teham
Junior Member
Username: Teham
Post Number: 21
Registered: 1-2004
| | Posted on Saturday, July 10, 2004 - 1:24 pm: | 
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I got my 490 working good. Found all tune ups except the mod. Is running about 30%. What do I turn to bring it up? Tony |
Tech808
Moderator
Username: Tech808
Post Number: 2912
Registered: 8-2002
| | Posted on Saturday, July 10, 2004 - 11:43 pm: |
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Teham,
Look to the left of the forum here and you will see:
Tools
Then you will see:
Modification List
CLICK ON IT.
Under MAKE type in: Realistic
Under MODEL type in: TRC-490
Hope this helps.
Lon
Tech808
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Teham
Junior Member
Username: Teham
Post Number: 27
Registered: 1-2004
| | Posted on Friday, August 13, 2004 - 6:35 am: |
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I found what to turn and also too out r 131. Still 30% so looks like the driver might be weak. Tony |
Tech808
Moderator
Username: Tech808
Post Number: 3287
Registered: 8-2002
| | Posted on Friday, August 13, 2004 - 8:23 am: |
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Teham,
Why did you remove R131?
In the Modification List to the left of the Forum Here under Tools it Shows:
Modulation ~ Cut R-104
AM Power ~ Adjust VR6
SSB Power ~ Adjust VR7
Try putting R-131 BACK in and Cut R-104.
Lon
Tech808
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Teham
Junior Member
Username: Teham
Post Number: 29
Registered: 1-2004
| | Posted on Friday, August 13, 2004 - 11:06 pm: |
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OK. Unsoldered it so can put it back. Will try 104. Tony |
Teham
Junior Member
Username: Teham
Post Number: 30
Registered: 1-2004
| | Posted on Saturday, August 14, 2004 - 12:09 am: |
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I now have 8-% I wrote down 104 then crossed it outand took 131. Can live with 80%. THNX Tony |
Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 241
Registered: 6-2004
| | Posted on Saturday, August 14, 2004 - 4:40 am: |
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Instead of cutting R104 you may try replacing it with a variable resistor so you can adjust the limiter rather than just disabling it entirely. I believe the value is 8.2 K ohm. It's very close to TR33 and D70 near the front of the radio on the right side when facing the radio.
Do you really need to modify it though? 30% modulation is about right for the average voice modulation level on AM. The human voice isn't capable of producing 100% average modulation because of it's dynamic range. It works out to about 30% unless a form of speech processing is used such as a microphone with compression like a Turner +3.
Try watching the power output for a few seconds with a constant tone like a whistle. If it's about twice the deadkey power then you're getting very good modulation. By definition, a 100% modulated AM signal will show twice the average power measurement of an unmodulated dead key. |
Cm3885
Advanced Member
Username: Cm3885
Post Number: 551
Registered: 12-2003
| | Posted on Saturday, August 14, 2004 - 3:03 pm: |
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Teham.
There are a few cool NPC/RC mods for this chassis that work great.
I think the 490 is like my Cobra 142 GTL in that the board is similar..
If you do the mods right you will be loud on AM and SSB both!!
have fun with this neat radio... :-) |
Cm3885
Advanced Member
Username: Cm3885
Post Number: 553
Registered: 12-2003
| | Posted on Saturday, August 14, 2004 - 3:11 pm: |
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30% modulation on AM????????
Dude, RU serious??????????
Yeah 30% might get you out for like 5 miles then your signal will be buried by all the noise and skip..
LOL! :-D
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Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 246
Registered: 6-2004
| | Posted on Saturday, August 14, 2004 - 7:25 pm: |
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Yes, I am serious. 30% AVERAGE modulation is all you'll get with voice modulation. There will be peaks of 100% modulation and also points of 0% modulation. The AVERAGE will work out to about 30% because of the dynamic range of the human voice. You can bump up the average modulation percentage by using a microphone with speech compression, or a speech processor. On some radios you can use an amplified microphone and drive the limiter to act as a speech processor, but it's generally not as good as a compression microphone or stand alone speech processor. |
Cm3885
Advanced Member
Username: Cm3885
Post Number: 554
Registered: 12-2003
| | Posted on Sunday, August 15, 2004 - 12:46 am: |
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Dude, im not trying to start an argument but I cant see were you come up with 30% modulation. If your radio does only 30% id either get it tuned up or dump it in the trash.. LOL
I mean every radio ive owned (and seen of others that i know that talk on the radio) have all been set up for 100%+ modulation. Even with an average voice ive seen anywere between 75 and 95% modulation.
This is what ive seen on my set up and my techs..
Im no tech but im no CB AMer dummy either. I just know what i see and know from what ive done...
What ive done all works for me!!! :-)
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Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 252
Registered: 6-2004
| | Posted on Sunday, August 15, 2004 - 2:22 pm: |
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If you are getting more than 30% average modulation with voice modulation you're doing one of three things:
1 - Using a speech processor of some kind - that could be using a power mic to drive the AMC to act as a crude speech processor, using a microphone with compression, or using a speech processor.
2 - You've clipped the limiter and are driving up the average modulation level by overmodulating a significant amount.
3 - You're watching a modulation meter. Modulation meters are not very accurate. They're basically something cool to watch while you chat. Actual modulation percentage can only be seen instantaneously on an oscilloscope or station monitor displaying your radio's output in a trapeziodal pattern.
30% average modulation level is about right for unprocessed speech on a radio with a limiter in tact and not driving the AMC to act as a speech processor.
I use compression microphones or stand alone speech processors when I want to have higher than normal average modulation levels. I can bump it up to as high as 90% if I really compress the dynamic range of my speech. Using a stock radio it sounds like I'm using an amplifier because I'm so loud. |
Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 254
Registered: 6-2004
| | Posted on Sunday, August 15, 2004 - 2:53 pm: |
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Forgot to add that I don't "tune up" radios because I don't think it's worth it. I'll do a little adjusting here and there for frequency and make sure the limiters are properly adjusted for 100% modulation and no more, but other than that I generally let things as they are from the factory.
I don't allow techs in my radios, and have walked out of CB shops that won't sell me a box stock radio that hasn't been opened up by them. I trust my own skills, and consider the skills of most CB techs to be suspect at best.
I've asked local techs to do a factory style alignment on radios, and they won't do it. I even provided them with the factory service manual or Sams manual, so it's not that they don't have the information. I don't think they have the necessary skills or equipment to do a full alignment. I don't have all of the necessary equipment or I'd do it myself. Fortunately I have radio friends who do have the necessary skills and equipment and will do it as a favor for me, but I hate to bother them when it really isn't necessary. There are a few pieces of test equipment I need that I haven't gotten around to acquiring, but I've found that I really don't need it because my radios work fine. |
Cm3885
Advanced Member
Username: Cm3885
Post Number: 556
Registered: 12-2003
| | Posted on Monday, August 16, 2004 - 1:35 am: |
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Well it sounds like to me you have a veritable drought of decent techs not to trust any of them..
I myself try to do as much light work (tune ups and light repairs) on my radios that i can.. The technical work i leave to my tech who in fact is a LISENSED tech with a 8 year degree in electronics. In fact hes one of the techs that used to work at Wawasee Electronics when they were hot and heavy in the mid 1970s.. He did all the tech work on those big amps that used to work on, build, and sell.
Im like you (Hey! You have mentioned one thing I agree with!) too about the buying of radios from shops that have worked on them. I will ONLY buy a radio brand new in the box that was sent directly from the factory.. I will NOT let any shop do pre work on a NIB radio. If they cant sell me a unopened factory fresh radio i wont buy one from them.. You never know what they did inside! :-( |
Teham
Junior Member
Username: Teham
Post Number: 32
Registered: 1-2004
| | Posted on Friday, August 20, 2004 - 6:40 am: |
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You can get 100% at least on every am radio. I have another problem. Seems as though someone before I got it played with a screwdriver. What do I turn to get am back on freq? Is 2 kc high. Tony |
499dx
New member
Username: 499dx
Post Number: 1
Registered: 1-2013
| | Posted on Saturday, January 12, 2013 - 7:01 pm: |
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I have a trc 490 and It won't modulate please help thanks |
499dx
New member
Username: 499dx
Post Number: 2
Registered: 1-2013
| | Posted on Saturday, January 12, 2013 - 7:02 pm: |
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I have a trc 490 and It won't modulate please help thanks |
Press_man
Advanced Member
Username: Press_man
Post Number: 705
Registered: 5-2008
| | Posted on Thursday, January 17, 2013 - 4:23 pm: |
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Cut R 104
VR 6 AM Power
VR 7 SSB Power
73 Pressman
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Wawa
New member
Username: Wawa
Post Number: 1
Registered: 3-2013
| | Posted on Saturday, March 30, 2013 - 12:02 am: |
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hi i have a trc-490 navaho base i had put away for ten yrs the receive is very weak only receive signals from a block away,transmitting very good and good modulation can anyone help me ????? |
Wawa
New member
Username: Wawa
Post Number: 2
Registered: 3-2013
| | Posted on Saturday, March 30, 2013 - 12:04 am: |
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i have a rci 2950 that work in ssb but not on am pls help... |
Milkman21218
Advanced Member
Username: Milkman21218
Post Number: 527
Registered: 1-2004
| | Posted on Saturday, March 30, 2013 - 8:59 pm: |
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To the new members WaWa, 499DX it would be better to start a new post with your own question. Than to add it to this old post that was started in 2004. Then just start by asking your question with a little info about your problem. You'll get help faster.
Izzy
CEF#502
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