Hi to all,

Hope that my question has some sense...: If we double the power
radiated by an antenna (+3 dB), how does it translate on the S-meter
at a receiver 'far' away.. i.e. is the difference in dB on that meter
has some mathematical relation to the 3 dB change at the transmitter?

73 de Pierre

On Sat, 18 Jul 2009 19:20:04 -0700 (PDT), ve2pid
wrote:

Hope that my question has some sense...: If we double the power
radiated by an antenna (+3 dB), how does it translate on the S-meter
at a receiver 'far' away.. i.e. is the difference in dB on that meter
has some mathematical relation to the 3 dB change at the transmitter?

One S unit is allegedly 6dB. Doubling the power would therefore be
about 1/2 an S unit.
http://en.wikipedia.org/wiki/S_meter
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Sat, 18 Jul 2009 19:20:04 -0700 (PDT), ve2pid
wrote:

Hope that my question has some sense...: If we double the power
radiated by an antenna (+3 dB), how does it translate on the S-meter
at a receiver 'far' away.. i.e. is the difference in dB on that meter
has some mathematical relation to the 3 dB change at the transmitter?

One S unit is allegedly 6dB. Doubling the power would therefore be
about 1/2 an S unit.
http://en.wikipedia.org/wiki/S_meter


I've heard the same thing, but the reality is that the S-meter usually
follows the AGC and the signal for S9 could be different for every design.
But Flex radio and others define S9 as 50 uV.

Long time past, I heard that S9 was a noise free signal. But "noise free"
is undefined. 30 dB SNR? 40 dB SNR?

Imagine that your S-meter is perfectly logarithmic and your SNR is 54 dB at
S9. That's one way to get 6 dB per S-unit.

Sal M. Onella wrote:

I've heard the same thing, but the reality is that the S-meter usually
follows the AGC and the signal for S9 could be different for every design.
But Flex radio and others define S9 as 50 uV. . .

Adjusting the S-meter to read a specific value for one signal strength
is simple, and there's often an adjustment for doing it. I think it's
fairly common to find S9 to be around 50 uV -- on one band at least --
although I wouldn't be surprised to see a fair amount of variation from
band to band. But that has nothing to do with what the difference is
between S7 and S8, S8 and S9, etc.

Roy Lewallen, W7EL

In message , Roy Lewallen
writes
Sal M. Onella wrote:
I've heard the same thing, but the reality is that the S-meter
usually
follows the AGC and the signal for S9 could be different for every design.
But Flex radio and others define S9 as 50 uV. . .

Adjusting the S-meter to read a specific value for one signal strength
is simple, and there's often an adjustment for doing it. I think it's
fairly common to find S9 to be around 50 uV -- on one band at least --
although I wouldn't be surprised to see a fair amount of variation from
band to band. But that has nothing to do with what the difference is
between S7 and S8, S8 and S9, etc.

Isn't there a school of thought which says that, above 1000MHz, an
S-point is 3dB? [Don't ask me why!]
--
Ian

In article ,
Ian Jackson wrote:

In message , Roy Lewallen
writes
Sal M. Onella wrote:
I've heard the same thing, but the reality is that the S-meter
usually
follows the AGC and the signal for S9 could be different for every design.
But Flex radio and others define S9 as 50 uV. . .

Adjusting the S-meter to read a specific value for one signal strength
is simple, and there's often an adjustment for doing it. I think it's
fairly common to find S9 to be around 50 uV -- on one band at least --
although I wouldn't be surprised to see a fair amount of variation from
band to band. But that has nothing to do with what the difference is
between S7 and S8, S8 and S9, etc.

Isn't there a school of thought which says that, above 1000MHz, an
S-point is 3dB? [Don't ask me why!]

there are "Many Schools of thought".... but unless someone rewrites the
Laws of Physics, and increase in Tx Output will show and Increase of Rx
Input, on the same path, period. S-meters are NOT necessarily actually
showing Rx Receive Signal Strength, and they are rarely, either linear,
or even Logrythmnic in presentation of what they do represent. In the
Microwave Field if you measure a path, and also calculate that path,
comparing the two will show that they are very close, if you did it
right....

ve2pid wrote:
Hi to all,

Hope that my question has some sense...: If we double the power
radiated by an antenna (+3 dB), how does it translate on the S-meter
at a receiver 'far' away.. i.e. is the difference in dB on that meter
has some mathematical relation to the 3 dB change at the transmitter?

73 de Pierre

No, none at all. S-meters almost always just measure the AGC voltage,
which is only approximately logarithmic. And manufacturers adjust the
sensitivity of the meter to please the customers, who don't like "dead"
meters. So the sensitivity of S-meters varies greatly from rig type to
type and from one end of the scale to the other. I measured the
sensitivity of the S-meter on my Icom 730 on one band. Here's how big an
S-unit is on my rig:

S1 - S2 1.4 dB
S2 - S3 1.3 dB
S3 - S4 1.6 dB
S4 - S5 2.3 dB
S5 - S6 1.8 dB
S6 - S7 3.2 dB
S7 - S8 3.1 dB
S8 - S9 4.0 dB
S9 - "S9 + 10 dB" 5.6 dB
"S9 + 10 dB" - "S9 + 20 dB" 7.3 dB
"S9 + 20 dB" - "S9 + 30 dB" 6.6 dB
"S9 + 30 dB" - "S9 + 40 dB" 10.5 dB
"S9 + 40 dB" - "S9 + 50 dB" 11.3 dB
"S9 + 50 dB" - "S9 + 60 dB" 13.5 dB

Now let's suppose that you built a new 5 element Yagi antenna and I
honestly reported that your signal went from S2 to S6 when you switched
to it from your dipole. The gain is really 7 dB, about par for the beam,
but you read the postings on the Web and decide that an S-unit is
"defined" as 6 dB, so the gain improvement must be 24 dB. Wow! Your
modest beam has the same gain as a beam with a 25 WAVELENGTH boom and
more than 50 elements! By making that incorrect assumption about the
sensitivity of my S-meter, you've overestimated the gain by a factor of 63.

S-meter sensitivities vary all over the map, so any assumption you make
about how many dB in an S-unit is very likely wrong, and often grossly
wrong.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
ve2pid wrote:
Hi to all,

Hope that my question has some sense...: If we double the power
radiated by an antenna (+3 dB), how does it translate on the S-meter
at a receiver 'far' away.. i.e. is the difference in dB on that meter
has some mathematical relation to the 3 dB change at the transmitter?

73 de Pierre

No, none at all. S-meters almost always just measure the AGC voltage,
which is only approximately logarithmic. And manufacturers adjust the
sensitivity of the meter to please the customers, who don't like "dead"
meters. So the sensitivity of S-meters varies greatly from rig type to
type and from one end of the scale to the other. I measured the
sensitivity of the S-meter on my Icom 730 on one band. Here's how big an
S-unit is on my rig:

S1 - S2 1.4 dB
S2 - S3 1.3 dB
S3 - S4 1.6 dB
S4 - S5 2.3 dB
S5 - S6 1.8 dB
S6 - S7 3.2 dB
S7 - S8 3.1 dB
S8 - S9 4.0 dB
S9 - "S9 + 10 dB" 5.6 dB
"S9 + 10 dB" - "S9 + 20 dB" 7.3 dB
"S9 + 20 dB" - "S9 + 30 dB" 6.6 dB
"S9 + 30 dB" - "S9 + 40 dB" 10.5 dB
"S9 + 40 dB" - "S9 + 50 dB" 11.3 dB
"S9 + 50 dB" - "S9 + 60 dB" 13.5 dB

Now let's suppose that you built a new 5 element Yagi antenna and I
honestly reported that your signal went from S2 to S6 when you switched
to it from your dipole. The gain is really 7 dB, about par for the beam,
but you read the postings on the Web and decide that an S-unit is
"defined" as 6 dB, so the gain improvement must be 24 dB. Wow! Your
modest beam has the same gain as a beam with a 25 WAVELENGTH boom and
more than 50 elements! By making that incorrect assumption about the
sensitivity of my S-meter, you've overestimated the gain by a factor of
63.

S-meter sensitivities vary all over the map, so any assumption you make
about how many dB in an S-unit is very likely wrong, and often grossly
wrong.

Roy Lewallen, W7EL

Nail on the head. A step attenunator in line will be the fastest way to
determine the linearity of your scale if you can't afford a calibrated
generator. FM rigs are all over the map on this because some radios have
better limiting than others, and it might be actual limiter reading or some
other derived reading.

In message , JB
writes
"Roy Lewallen" wrote in message
m...
ve2pid wrote:
Hi to all,

Hope that my question has some sense...: If we double the power
radiated by an antenna (+3 dB), how does it translate on the S-meter
at a receiver 'far' away.. i.e. is the difference in dB on that meter
has some mathematical relation to the 3 dB change at the transmitter?

73 de Pierre

No, none at all. S-meters almost always just measure the AGC voltage,
which is only approximately logarithmic. And manufacturers adjust the
sensitivity of the meter to please the customers, who don't like "dead"
meters. So the sensitivity of S-meters varies greatly from rig type to
type and from one end of the scale to the other. I measured the
sensitivity of the S-meter on my Icom 730 on one band. Here's how big an
S-unit is on my rig:

S1 - S2 1.4 dB
S2 - S3 1.3 dB
S3 - S4 1.6 dB
S4 - S5 2.3 dB
S5 - S6 1.8 dB
S6 - S7 3.2 dB
S7 - S8 3.1 dB
S8 - S9 4.0 dB
S9 - "S9 + 10 dB" 5.6 dB
"S9 + 10 dB" - "S9 + 20 dB" 7.3 dB
"S9 + 20 dB" - "S9 + 30 dB" 6.6 dB
"S9 + 30 dB" - "S9 + 40 dB" 10.5 dB
"S9 + 40 dB" - "S9 + 50 dB" 11.3 dB
"S9 + 50 dB" - "S9 + 60 dB" 13.5 dB

Now let's suppose that you built a new 5 element Yagi antenna and I
honestly reported that your signal went from S2 to S6 when you switched
to it from your dipole. The gain is really 7 dB, about par for the beam,
but you read the postings on the Web and decide that an S-unit is
"defined" as 6 dB, so the gain improvement must be 24 dB. Wow! Your
modest beam has the same gain as a beam with a 25 WAVELENGTH boom and
more than 50 elements! By making that incorrect assumption about the
sensitivity of my S-meter, you've overestimated the gain by a factor of
63.

S-meter sensitivities vary all over the map, so any assumption you make
about how many dB in an S-unit is very likely wrong, and often grossly
wrong.

Roy Lewallen, W7EL

Nail on the head. A step attenunator in line will be the fastest way to
determine the linearity of your scale if you can't afford a calibrated
generator. FM rigs are all over the map on this because some radios have
better limiting than others, and it might be actual limiter reading or some
other derived reading.

You'll need an adequately-screened signal generator to do this test. If
it isn't, the signals which leak out can bypass the attenuator and enter
a not-too-well-screened receiver. If this happens, the results you get
will be false.
--
Ian

"Ian Jackson" wrote in message
...
In message , JB
writes
"Roy Lewallen" wrote in message
m...
ve2pid wrote:
Hi to all,

Hope that my question has some sense...: If we double the power
radiated by an antenna (+3 dB), how does it translate on the S-meter
at a receiver 'far' away.. i.e. is the difference in dB on that meter
has some mathematical relation to the 3 dB change at the transmitter?

73 de Pierre

No, none at all. S-meters almost always just measure the AGC voltage,
which is only approximately logarithmic. And manufacturers adjust the
sensitivity of the meter to please the customers, who don't like "dead"
meters. So the sensitivity of S-meters varies greatly from rig type to
type and from one end of the scale to the other. I measured the
sensitivity of the S-meter on my Icom 730 on one band. Here's how big
an
S-unit is on my rig:

S1 - S2 1.4 dB
S2 - S3 1.3 dB
S3 - S4 1.6 dB
S4 - S5 2.3 dB
S5 - S6 1.8 dB
S6 - S7 3.2 dB
S7 - S8 3.1 dB
S8 - S9 4.0 dB
S9 - "S9 + 10 dB" 5.6 dB
"S9 + 10 dB" - "S9 + 20 dB" 7.3 dB
"S9 + 20 dB" - "S9 + 30 dB" 6.6 dB
"S9 + 30 dB" - "S9 + 40 dB" 10.5 dB
"S9 + 40 dB" - "S9 + 50 dB" 11.3 dB
"S9 + 50 dB" - "S9 + 60 dB" 13.5 dB

Now let's suppose that you built a new 5 element Yagi antenna and I
honestly reported that your signal went from S2 to S6 when you switched
to it from your dipole. The gain is really 7 dB, about par for the
beam,
but you read the postings on the Web and decide that an S-unit is
"defined" as 6 dB, so the gain improvement must be 24 dB. Wow! Your
modest beam has the same gain as a beam with a 25 WAVELENGTH boom and
more than 50 elements! By making that incorrect assumption about the
sensitivity of my S-meter, you've overestimated the gain by a factor of
63.

S-meter sensitivities vary all over the map, so any assumption you make
about how many dB in an S-unit is very likely wrong, and often grossly
wrong.

Roy Lewallen, W7EL

Nail on the head. A step attenunator in line will be the fastest way to
determine the linearity of your scale if you can't afford a calibrated
generator. FM rigs are all over the map on this because some radios have
better limiting than others, and it might be actual limiter reading or
some
other derived reading.

You'll need an adequately-screened signal generator to do this test. If
it isn't, the signals which leak out can bypass the attenuator and enter
a not-too-well-screened receiver. If this happens, the results you get
will be false.
--
Ian

Good point. If the signal is off the air it is less likely to be an issue.
You need to seriously work on your setup to get better than 60 db of
resolution. I homebrewed the 3, 6, 10, 20 step attenuator from one of the
ARRL publications and find it quite useful. Output cable is double
shielded.