Lee
Yes, this is confusing as it can get. Any passive component adds noise, any
active components adds noise. Power noise, and you only can add power noise
converting it in equivalent temperature in Kelvin degree.
The antenna itself is another confusing thing, any antenna has directivity
gain and power gain, when the efficiency in near 100% the power gain is the
same as directivity gain and most just say antenna gain, this assumes power
factor 1, no loss.
EZENEC gain calculation for loops near ground is not perfect as well, If you
build a loop and measure the mv/m you find a surprised difference between
EZNEC power gain. Directivity gain is really RDF by definition so the HWF
and VWF has 11.5 directivity gain and let's say a very low power gain, the
system have losses.
The receiving systems starts at the preamp. Even if it's near the antenna,
far from the radio, or near the radio. The calculation is the same.
The S meter in most analog radio measures the AGC, in SDR radios it can be
calibrates in dBm at the input of the preamp. That can be consider operator
preferences.
Power noise, power gain, voltage gain can be very confusing because the real
input or output impedance .
The discussion is really about the signal to noise ratio near the noise
floor of the receiver system. If you use you S meter at the input of the
preamp or after the preamp, it does not change the signal to noise ratio.
Small loops also have thermal noise itself and can be a limit factor as
well.
>>
So in order to simply match the noise level of .446 uVolts with a signal you
need a signal impinging on this antenna that would produce 79 uVolts in an
antenna similar to the reference.
<<
I really don't understand you point can you elaborate it?
Regards
JC
N4IS
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Lee K7TJR
Sent: Tuesday, September 08, 2015 4:01 PM
To: topband@contesting.com
Subject: Topband: Waller Flag
I must be missing something.
The noise in a 50 ohm resistor is -174 dbm per root Hz at ambient temp.
Lets take 100Hz bandwidth for the receiver and the noise becomes -154 dbm or
.0045 uVolts
Lets add a PERFECT amplifier of 40 db. The noise output of the 40 db amp is
then -114 dbm or 0.446 uVolts
S-2 on a receiver with perfect S meter is .4 uVolts so the RX should set at
S-2 normally.
As I understand it the Waller antenna produces about -45 db of gain over
some reference. (45 db Is 177 time voltage)
To me a signal of 79 uVolts is something over S-9 on a receiver. Would a
simple dipole or inverted Vee antenna with essentially no gain produce a
whopping signal from the same source. Of course it would pick up noise as
well but I would think it would not be of an equal S-9 level.
Where did I go wrong in these figures. I must be astray somewhere.
Lee K7TJR OR
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