| Author |
Message |
    
Wally38
Member
Username: Wally38
Post Number: 74
Registered: 3-2005
| | Posted on Friday, February 10, 2006 - 3:59 pm: | 
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I live about 30 to 40 miles away from Interstate 80 where there is ALOT of trucker talk on channel 19. If I point my Shooting Star towards the Interstate I can hear many voices, but cannot tell what they are saying. Just on the edge of my receive. Do you think a preamp with a 25db gain would pull them right in? |
Tech808
Moderator
Username: Tech808
Post Number: 9260
Registered: 8-2002
| | Posted on Friday, February 10, 2006 - 4:24 pm: |
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Wally38,
YES, a 25db Pre-Amp would be a BIG help to you.
Lon
Tech808
CEF808
N9CEF |
Wildrat
Advanced Member
Username: Wildrat
Post Number: 773
Registered: 12-2003
| | Posted on Friday, February 10, 2006 - 4:46 pm: |
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yep, yep |
Hotwire
Advanced Member
Username: Hotwire
Post Number: 890
Registered: 1-2005
| | Posted on Saturday, February 11, 2006 - 8:53 am: |
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Wally man you are lucky! I live 1 mile away from I-65 in Indiana. At least you can turn the preamp OFF! If I hear one more trucker say he don't have any pantys on I'm gonna sale all my stuff on the front lawn! |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1078
Registered: 6-2004
| | Posted on Saturday, February 11, 2006 - 3:36 pm: |
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Pre-amplifiers amplify noise as well as signal, so you'd have to have at least a bit more signal than noise for the amplifier to help. The pre-amplifier also adds noise to the signal, so you may have a little more signal now, but when you use the amplifier it may just fade into the noise.
Personally I've never had much luck with them on CB or scanning VHF/UHF. I have an active antenna for SWL that works pretty well, but it also adds selectivity and sometimes the added selectivity is worth more than the amplification.
You're always better off using a higher antenna, an antenna with more gain, better coax, and/or a more sensitive radio.
One suggestion if you do decide to use a preamp - look into one that installs near the antenna and still allows you to transmit. There are some 10 meter pre-amplifiers that do this, and it will allow you to overcome the loss of the coax on RX. They are more expensive though. |
Wally38
Member
Username: Wally38
Post Number: 75
Registered: 3-2005
| | Posted on Saturday, February 11, 2006 - 4:32 pm: |
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I just bought the one that Copper Electronics sells. It's on it's way! I can't wait to try it out.
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Georgeodjungle
Junior Member
Username: Georgeodjungle
Post Number: 30
Registered: 1-2006
| | Posted on Sunday, February 12, 2006 - 2:18 pm: |
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to perform better:
preamps can be tweeked.
just like radios, tvs what ever.
just your favorite tech...
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Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1081
Registered: 6-2004
| | Posted on Sunday, February 12, 2006 - 3:05 pm: |
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Just how would you go about doing that? What would tweeking accomplish? |
Georgeodjungle
Junior Member
Username: Georgeodjungle
Post Number: 32
Registered: 1-2006
| | Posted on Sunday, February 12, 2006 - 11:22 pm: |
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oops:
i ment to say:
just get a hold of your favorite tech...
a good one will know what to do.
tweeken a preamp will reduce the hash and trash.
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Bruce
Senior Member
Username: Bruce
Post Number: 3529
Registered: 9-2003
| | Posted on Monday, February 13, 2006 - 8:26 am: |
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to perform better: preamps can be tweeked.
just like radios, tvs what ever.
just your favorite tech...
Ok lets look at this .....PREAMPS 101
Preamps CAN make a diffrence if the noise is very low. Most clame 25 db of gain but at what noise figure? If your radio has a 3 db noise figure RF stage placeing a 4 db noise preamp in frount of it will only make things worse.
"tweeken a preamp will reduce the hash and trash"
Now unless your tech has a NOISE FIGURE METER HE CANNOT tweek ANY PREAMP however he might retune the center frequency but that will not gain you much.
Again it's not the gain its the reduction in NOISE that counts ...
Lets look at this the idea behind " PREAMPS " is not gain but to lower the FIRST STAGE NOISE FIGURE ( AKA better and lower noise floor )
For example if @ 6 db AM bandwidth a 3 DB first stage gives you - 107 dbm ( 1 UV ) what would you gain if you added a 25 db gain preamp 4db of noise? ..... YES your meter would read higher but when the signal got down to -107 DBM it would already be gone burried in noise. The same preamp with a .5DB noise figure would now hear the signal down to about -112 dbm ( about .6UV )and your meter would STILL read higher! NOW WE ARE GETTING SOMEWHERE !
You must remember this is ONLY if the background is SO low that you can make use of this kind of gain..... other wise its going to get covered up bu external noise.
On the 6 meter band preamps are widely used on older radios the new ones have noise floors down into the .1 UV range ( -127 DBM ) and can easly hear the lowest background noises .... most newer sets like FT-100, IC-706 and IC-7000 have a preamp built in.
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Tech291
Moderator
Username: Tech291
Post Number: 367
Registered: 11-2004
| | Posted on Monday, February 13, 2006 - 9:02 pm: |
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good post Bruce!
TECH291
CEF#291
KC8ZPJ |
Georgeodjungle
Junior Member
Username: Georgeodjungle
Post Number: 33
Registered: 1-2006
| | Posted on Tuesday, February 14, 2006 - 12:56 am: |
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ya ya
good post.
i'm glad i got a great cb guru.
i took a palamar 200 to him to see what he could do and presto!
it hears better than it did.
i don't know how or what got done.
i'm not at that level yet.
looks like a coil a cap got added.
but back to ?
yes a preamp will help. |
Bruce
Senior Member
Username: Bruce
Post Number: 3535
Registered: 9-2003
| | Posted on Tuesday, February 14, 2006 - 7:47 am: |
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George most cb sets can hear background noise all a preamp will do is increase that.
As for you can hear better I would like to see before and after test done with good equiptment ..... and see what the before and after noise floor test showed.... The human ear is poor at best and if you rase the gain it will sound better but you will still lose the signal at the same point .... just you meter will be reading higher.
2 Meter amps have preamps and i have found them to DEGRADE signals because the radios have got so good. It's the NOISE FIGURE not gain that counts in the first stage ...... even on cb.
I have seen CB preamps with .2DB noise figures now one of them would be a killer at 27 mhz ..... |
Bruce
Senior Member
Username: Bruce
Post Number: 3536
Registered: 9-2003
| | Posted on Tuesday, February 14, 2006 - 8:25 am: |
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Here is a short peice on building a preamp
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=9258 |
