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What will +3 dB do for me? Help Please

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kc8qln

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Here is my current situation

Antenex FG8243 antenna (+3dB Gain), mounted on a 5 foot mast on my roof.
LMR400 cable 60 feet - No adaptors
RS PRO-2096 scanner
Roof Elevation ~700 ft.

Obviously, I get more 800 Mhz systems with the Antenex on my roof than just using the indoor antenna, but not a much as I would have hoped for. Some towers 25-30 miles out I can't seem to pick up.

What if I upgraded to an Antenex FG8246, which is +6 dB of gain?

In relative (or even layman's terms), what more of an advantage would going from +3dB to +6 dB get me? Would it be worth it buy a new antenna and try it?

Thanks
 

mass-man

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Big D, little a, double l, a s
Hmmm...

I may get corrected here, but the gain figures are for TRANSMITTING! At least that is the way it has been explained to me for years. What you have are several tuned antennas tuned for 800 in one case, but more gain is NOT going to give you better receiving properties.

That said, I would wait for the comments before buying a new antenna. It would seem you could heard way better at 700ft.. But that said, the 800 antennas are capable of having their signals tuned in a downward pattern. It may be the systems you want to hear, DON"T you to hear them, and to be better heard in their city, are tuned downward, much like an umbrella.

If the systems you want to hear are all the same direction from you, a BEAM is your best bet.

Ah, let the flames begin!!!
 

NeFire242

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And for every 3dB you are essentially doubling your signal strength, but he's right, you'd need a pre-amp or something for the receive side. I'd try an 800 beam too and point it right towards the tower site and see what that does.
 
N

N_Jay

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1) The gain of an antenna is symmetrical TX and RX.

If it is 3 dB on TX it is 3 dB on RX

2) 3 db change will be hardly noticed.

Yes it is "double the power" but don't let that confuse you. 3 dB is a relatively small change in receiver level. The difference between a clear signal and a noisy signal is typically 6 to 18 dB.

3) How tall is your roof? What nearby obstructions are around?

Doubling your effective antenna height (above local terrain) will give you about 6 dB.

4) The signal strength at your location is definitely a function of the repeater site antenna system. It may have down-tilt or it may be designed with very little signal in your direction.
 

murrayustud

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I'm in Raleigh, NC & am using a similar set up with a couple exceptions: I utilize 2 different 800mhz antennas, 1 a Cushcraft Omni-directional, the other a 3 element Cushcraft 800mhz beam pointed west. Both antennas are approx 34 feet above ground. Both are fed with LMR-400 no adapters, then fed thru a 10db pre-amp. The pre-amp made a HUGE difference for me as I was trying to receive Durham, NC's 800mhz system which is weak & problematic even in Durham which is about 31 miles north west of my location. With the pre-amp & the beam I get them 90% quieting, without it they are quite noisy. The pre-amp was about $20 on Ebay--
Chaeles
 
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Gilligan

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murrayustud said:
Both are fed with LMR-400 no adapters, then fed thru a 10db pre-amp. The pre-amp made a HUGE difference for me as I was trying to receive Durham, NC's 800mhz system which is weak & problematic even in Durham which is about 31 miles north west of my location. With the pre-amp & the beam I get them 90% quieting, without it they are quite noisy. The pre-amp was about $20 on Ebay--
Chaeles
Wow! $20 for 10db! What kind of preamp is that? I'd love to find one like that myself. What's the model?
 

rbm

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kc8qln said:
In relative (or even layman's terms), what more of an advantage would going from +3dB to +6 dB get me? Would it be worth it buy a new antenna and try it?
Thanks
On strong signals you will see little or no difference.

On very weak signals you should notice quite a bit of improvement. A 3dB improvement on a signal that is lost in the noise 'may' become strong enough to be heard clearly, even if still not full quieting.

The additional gain 'may' come close to overcoming the loss of your coax at that frequency range.
 
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N_Jay

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rbm said:
On strong signals you will see little or no difference.

On very weak signals you should notice quite a bit of improvement. A 3dB improvement on a signal that is lost in the noise 'may' become strong enough to be heard clearly, even if still not full quieting.

The additional gain 'may' come close to overcoming the loss of your coax at that frequency range.
Don't get too excited.

If the signal is just a little noisy, you might get it a little clearer.

If it is very noisy, it is going to stay very noisy (just a little, noticeable, but not much more).

Find a friend with a service monitor, and have him show you the improvement of 3 dB.

Or go find a splitter with known loss and insert it in your antenna line.
 

richardc63

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I'm surprised no-one has pointed out that the 10dB of gain would be better placed at the antenna, before the cable loss reduces the signal available to be amplified. What is more important is not the amount of signal, but how great is the ratio of signal to noise. That can be better increased by using a masthead amplifier.

Cheers,


Richard
N_Jay said:
Don't get too excited.

If the signal is just a little noisy, you might get it a little clearer.

If it is very noisy, it is going to stay very noisy (just a little, noticeable, but not much more).

Find a friend with a service monitor, and have him show you the improvement of 3 dB.

Or go find a splitter with known loss and insert it in your antenna line.
 
N

N_Jay

Guest
Well, it was not an amplifier thread.;)

(Hey, I'm working on staying "on-topic", give me some credit):lol:

As for my opinion on Amplifiers, do a search, there is plenty there.:D
 

NeFire242

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Could go all out and build a 200' tower with an array of beams of various bands with tower top amps and LMR400 down to the scanner. =)
 

kf4lne

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Bristol, VA
NeFire242 said:
Could go all out and build a 200' tower with an array of beams of various bands with tower top amps and LMR400 down to the scanner. =)
buy some property on a hill overlooking the city, build a home, install a 300 ft cell phone style tower behind the home, lease spaces on the tower to the police, FD, SD and whoever else you want to listen to. No need to buy a scanner antenna then.
 

grem467

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Houston, TX
antennas dont have "gain" in the same sense as an amplifier, as they cannot amplify anything.

the "gain" is a misnomomer and is merely a comparason of one antenna to another, typically a 1/4 wave radiator (dBd), but sometimes is compared to a theoretical isotropic antenna (dBi).

Capture area and the antennas pattern is much more important to consider, as sometimes a "gain" antenna with low radiation angle might be outperformed by a 1/4w whip which has more of a "bubble" type pattern.

the best antenna depends on your specfic application
 

prcguy

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6dB per “S” unit and 100uv for “S9” used to be the standard until the Japanese adopted 50uv for “S9” somewhere in the 1960’s. Most radios are not very linear and you can see anywhere from a 2 to 10dB change per “S” unit or worse.
prcguy
Cuda61 said:
If I remember right, You will have to increace the recieve signal by 9db to raise your siginal strength one S-unit.
 
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