dB relation TX/RX
 

In message , AE5NE
writes
On Sun, 19 Jul 2009 07:31:01 -0700, Jitt wrote:

In article 753fee20-bfec-4b9a-81b2-
, says...
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

Only in theory. It is possible to write an expression
which relates an increase in Tx power to Rx antenna power at the remote
site, but I doubt if it would agree with observed values in the field.


If they did not - any linear mode such as SSB would have a pretty hard
time working!

Aye, Captain. Ye canna change the laws of physics.
--
Ian

dB relation TX/RX
 

http://www.arrl.org/notes/hbk-templates/stepatt.pdf
This is the one I based mine on. Fewer sections. The Slide switches are
superior because of lower inductance and the bulkheads help with
isolation.
I found there was another version in the TIS section:
http://www.arrl.org/tis/info/pdf/9506033.pdf

As the pictures show, there is screening between the switches (even
though it's a bit skimpy on the second unit). Even in the first, for the
ultimate in isolation, it would be even better if there was an RF gasket
on the inside of the top cover which, when screwed down, makes contact
with the tops of all the screens, and makes each switch compartment
virtually watertight.

Tin plated solder wick

dB relation TX/RX
 

You figure out these things when you have more time than money or sense. I
might not make it to mars before someone with a budget though.

Actually it turns out the second version might have better isolation,
because it turns out coupling between the resistors and the switch terminals
is more unwanted than between the attenuator sections themselves. But it is
wise to remember that probably 20db at each switch is the most to be
expected because of the coupling within the switch. It is probably a good
thing to compartmentalize also, to realize a maximum combined attenuation
with all sections engaged. His worry seemed to be trying to keep 50 ohms
between sections when all switches are bypassed, but I doubt that there is
50 ohms through the switches themselves. Of course if any section is
engaged, the return loss would make it a moot point.

I guess in the end, the switch itself becomes the limiting factor in the
performance of the thing, as with any RF switching project. Hard to find
non-inductive resistors too but surface mount chips might be a good answer
to that.

dB relation TX/RX
 

In message , JB
writes
http://www.arrl.org/notes/hbk-templates/stepatt.pdf
This is the one I based mine on. Fewer sections. The Slide switches are
superior because of lower inductance and the bulkheads help with
isolation.
I found there was another version in the TIS section:
http://www.arrl.org/tis/info/pdf/9506033.pdf

As the pictures show, there is screening between the switches (even
though it's a bit skimpy on the second unit). Even in the first, for the
ultimate in isolation, it would be even better if there was an RF gasket
on the inside of the top cover which, when screwed down, makes contact
with the tops of all the screens, and makes each switch compartment
virtually watertight.

Tin plated solder wick

Many CATV modules use a gasket made from the equivalent of a sheet of
spongy foam rubber/plastic backed with BacoFoil.
--
Ian

dB relation TX/RX
 

No one is disagreeing. S-meters are renowned liars. Mind you, I have a CB set
(which has an AGC line) which is converted to 10m, and this has an S-meter
which has remarkably consistent 6dB S-points between S2 and S9 +20dB.

Even considering an ideal S-meter having a perfect one-S point-per-6 dB
response, the answer to the original question is that only in theory doubling
the transmit power turns into a 3-dB increase in S-meter reading.

In practice what the S-meter "measures" is the sum of the "wanted" signal power,
plus the background noise power (which on e.g. 160 meters could be quite high),
plus possibly the power other signals falling in the receiver bandwidth. If the
wanted signal is not strong enough to overwhelm al other contributions, doubling
the transmit power will not turn into a 3-db S-meter reading increase.

73

Tony I0JX, Rome Italy


:

If we double the power
radiated by an antenna (+3 dB), how does it translate on the S-meter
at a receiver 'far' away..

dB relation TX/RX
 

On Wed, 22 Jul 2009 18:34:46 +0200, "Antonio Vernucci"
wrote:

Even considering an ideal S-meter ... If the
wanted signal is not strong enough to overwhelm al other contributions, doubling
the transmit power will not turn into a 3-db S-meter reading increase.

It would have to. Any additional power to the general spectrum is
going to raise the power in the spectrum - even if you cannot
distinguish it. That is, afterall, how the spectrum gets to become so
noisy. If you are tuned to the radiator that has gone through a power
boost, then your S-Meter should indicate it.

73's
Richard Clark, KB7QHC

dB relation TX/RX
 

Even considering an ideal S-meter ... If the
wanted signal is not strong enough to overwhelm al other contributions,
doubling
the transmit power will not turn into a 3-db S-meter reading increase.

It would have to. Any additional power to the general spectrum is
going to raise the power in the spectrum - even if you cannot
distinguish it. That is, afterall, how the spectrum gets to become so
noisy. If you are tuned to the radiator that has gone through a power
boost, then your S-Meter should indicate it.

73's
Richard Clark, KB7QHC

Yes, but not quite 3dB when transmit power is doubled. A 3-dB increase would
only occur if the "wanted" signal would be alone in the receiver bandwidth (viz
no background noise, no interfering signal).

73

Tony I0JX

dB relation TX/RX
 

On Wed, 22 Jul 2009 19:35:40 +0200, "Antonio Vernucci"
wrote:

Yes, but not quite 3dB when transmit power is doubled.

It would be dependent upon S+N/N, yes.

73's
Richard Clark, KB7QHC