db gain ?

[mriley7212]

I have a radio shack upgrade antenna on a pro 96 and would like to get a better antenna. I see many with 2.5, 3 and 5 db gain. What does this mean? Is the gain relative to distance, so a 5db gain will reach 5 times farther. :?:

What is the best one to buy?

Thanks,

Mike

 

[N_Jay]

I have a radio shack upgrade antenna on a pro 96 and would like to get a better antenna. I see many with 2.5, 3 and 5 db gain. What does this mean? Is the gain relative to distance, so a 5db gain will reach 5 times farther. :?:

What is the best one to buy?

Thanks,

Mike

Antenna gain is measured in dB.

3dB is twice the gain, 10 dB is ten times the gain.

It is a log scale and usually the reference point is standard antenna of some type.
dBd is dB reference a dipole
dBi is dB reference a theoretical isotropic radiator. (Theoretical perfect 0 dB antenna)

Without a reference dB is meaningless.
In antenna advertisements it is only a little better

Think HP specs on cars in the early 1960's :evil:

There are no good rules of thumb for how much further you can hear with a given amount of gain.

 

[kb2vxa]

Hi all,

"3dB is twice the gain, 10 dB is ten times the gain. It is a log scale..."

That statement is contradictory, do the math correctly next time. For every 3dB the signal doubles. For example, take a 4W CB signal into a dipole. It produces 4W ERP, but 3dB gives 8W ERP, another 3 and you have 16W ERP. Just adding one more dB won't jump the signal to 40W ERP by any stretch of the imagination, 3 more and you have 32W ERP. That's power gain, for receive you have to calculate dB/uV which to state it simply the received signal doubles with every 6dB, your thinking of dB/W.

The bottom line is dBi is lower than dBd because an isotropic radiator is a theoretical point source radiating equally well in all directions, a spherical pattern. No such thing exists in the real world, refereced to a dipole or groundplane (dBd) is realistic. Manufacturers rely on snake oil salesmen to hype specs so take it all with a grain of salt.

Now I'm off to Sesame Street where Kermit is singing Rubber Duckie. While he's having fun in the bath tub I'll toss in a few dBs with my rubber duck antenna and watch him jump. (;->)

The only gain antennas are single band colinears and beam types, rhombic, Sterba curtain, log periodic, helical, Yagi and such. Bandwidth vs. gain is an important factor, wider bandwidth, less gain and vice versa.

 

[N_Jay]

Hi all,

"3dB is twice the gain, 10 dB is ten times the gain. It is a log scale..."

That statement is contradictory, do the math correctly next time. For every 3dB the signal doubles. For example, take a 4W CB signal into a dipole. It produces 4W ERP, but 3dB gives 8W ERP, another 3 and you have 16W ERP. Just adding one more dB won't jump the signal to 40W

Let's try some simple math.
1 Watt
3 dB more is 2W (Total 3 dB)
2 Watts
3 dB more is 4W (Total 6 dB)
4 Watts
3 dB more is 8W (Total 9 dB)
8Watts
1 dB more is 10 W (Total 10dB)

(You missed a doubling!)

That's power gain, for receive you have to calculate dB/uV which to state it simply the received signal doubles with every 6dB, your thinking of dB/W.

Very true, if you are concerned with a doubling of a voltage then you need 6dB (But everyone knows that!)

Maybe I'm old-school, but I do my receive calculations is dBm. and all the simple power rules apply.

The bottom line is dBi is lower than dBd because an isotropic radiator is a theoretical point source radiating equally well in all directions, a spherical pattern. No such thing exists in the real world, refereced to a dipole or groundplane (dBd) is realistic. Manufacturers rely on snake oil salesmen to hype specs so take it all with a grain of salt.

On that we agree (remember my 1960's HP reference)

The only gain antennas are single band colinears and beam types, rhombic, Sterba curtain, log periodic, helical, Yagi and such. Bandwidth vs. gain is an important factor, wider bandwidth, less gain and vice versa.

Excuse me????

What about linear panel arrays? Corner reflectors? Parabolic dishes?

The REAL IMPORTANT thing for everyone to learn is that "gain" is ONLY meaningful when you know the reference point.

I heard a 2" stub has 40 to 60 dB gain at 150 MHz (Over a dummy load) :twisted: :twisted:

 

[Al42]

Hi all,

"3dB is twice the gain, 10 dB is ten times the gain. It is a log scale..."

That statement is contradictory, do the math correctly next time. For every 3dB the signal doubles. For example, take a 4W CB signal into a dipole. It produces 4W ERP, but 3dB gives 8W ERP, another 3 and you have 16W ERP. Just adding one more dB won't jump the signal to 40W

Let's try some simple math.

I'm glad someone else can still handle antenna gain.

(You missed a doubling!)

Yep. 7db gain definitely won't turn 4 watts erp into 40 watts erp.

 

[WileECoyote]

Now I'm off to Sesame Street where Kermit is singing Rubber Duckie. While he's having fun in the bath tub I'll toss in a few dBs with my rubber duck antenna and watch him jump. (;->)

Kermit never had or sang rubber duckie, it was Ernie.
Trust me, I have 4 kids. :lol:

 

[kb2vxa]

Hi all,

OK, you got me, guilty as charged on both counts. You can't expect me to list ALL beam type antennas any more than know every detail of Sesame Street, especially since Kermit and Ernie both sound like Frank Oz. (;->)

"Maybe I'm old-school, but I do my receive calculations is dBm. and all the simple power rules apply."

OK smarty pants, what is the new 0dB reference and how does it differ from the old one? Bonus question: How does it compare to 0 VU? Double bonus question: Which antenna is also known as "Jane, you ignorant slut."?

This has been a Bustaneardrum production in cooperation with PowZap studios and KB2VXA Radio Destrductions. Opinions expressed on this program do not necissarily reflect those of anyone living or dead, Grateful Dead, Anna Bofanna Mo-Anna, Rosanna Rosannadanna or Emily Latella. Names have been changed to protect the guilty.

 

[N_Jay]

. . . . You can't expect me to list ALL beam type antennas any more than know every detail of Sesame Street, . . . (;->)

OK smarty pants, what is the new 0dB reference and how does it differ from the old one? Bonus question: How does it compare to 0 VU?

Dude, you got on the wrong side of the bed, BIG TIME!

1) I was not the one who said;
"The only gain antennas are single band colinears and beam types, rhombic, Sterba curtain, log periodic, helical, Yagi and such."
You were!
P.S. Don't use the word "ONLY" unless you mean "ONLY". Duh! (Duh, added for clarity)

2) As I have said MANY TIMES, dB is relative measure, so if you don't know the reference it is meaningless.

So 0dB does not have a reference until you assign one.

3) dBm is reference 1 miliwatt. Is the old (and new) standard for power on most systems other than transmitters.

Power is a much more appropriate way to measure signal strength than any voltage unit. (yes field strength is measures in Volts per Meter, but once it is "IN" a system watts is easier/better/more appropriate.

4) VU is Volume Units, which are only used (properly) in audio systems.
They are relative the desired signal power at any particular point in the system. They have no direct relationship to power, and some question the assignment of dB as the unit since they are not always calibrated.