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:[email protected]] On Behalf Of Lee K7TJR Sent: Tuesday, September 08, 2015 4:01 PM To: [email protected] 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 _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
