Actually the signal is not 3 dB above the noise floor with the procedure described, The (S+N)/N is 3 dB, thus the signal and noise are at the same level. If one has a good estimate of the noise power bandwidth of the 500 Hz filter, it then becomes easy to calculate the NF of the receiver system. Lester B Veenstra MØYCM K1YCM US Postal Address: PSC 45 Box 781 APO AE 09468 USA UK Postal Address: Dawn Cottage Norwood, Harrogate HG3 1SD, UK Telephones: Office: +44-(0)1423-846-385 Home: +44-(0)1943-880-963 UK Cell: +44-(0)7716-298-224 US Cell: +1-240-425-7335 Jamaica: +1-876-352-7504 _____
From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Guido Sent: Thursday, May 22, 2008 6:29 AM To: [email protected] Subject: Re: [softrock40] Re: MDS of Lite+XTALL v.8.3 David, >From Bodo's response, I interprete it as: first, calibrate with signal generator, then second, terminate with 50R and measure noise power. Bodo's justification why this is a MDS measurement, is that when a signal of equal power is injected, it can be received at 3 dB above the noise level. Guido. On Thu, May 22, 2008 at 6:44 AM, drmail377 <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> com> wrote: So you measure the received power in 500Hz with 50 Ohm termination on the antenna input, then replace the antenna with the generator and increase the signal power until you see a 3dB increase in the receive power, the generator output level is then the MDS level? Is my interpretation correct? I wish there was a standardized procedure for this. Rgds, David --- In [EMAIL PROTECTED] <mailto:[email protected]> ups.com, "ad9850" <[EMAIL PROTECTED]> wrote: > > Hi, > > I am following a very simple procedure described some time ago by Bob, > N4HY in the old FlexRadio forum. I am measuring the noise power in 500 > Hz bandwidth, the antenna input terminated by 50 ohms. This is the MDS > because a signal of equal power will increase the level by 3 dB. I am > using Duncans KGKSDR to determine the power in 500 Hz bandwidth. The > software is calibrated for each band. A Rohde&Schwarz signal generator > is used for the calibration. > > 73 Bodo, DJ9CS > > > --- In [EMAIL PROTECTED] <mailto:[email protected]> ups.com, "Alan" <g4zfq@> wrote: > > > > > > ----- Original Message ----- > > From: "ad9850" > > > > > > sorry I forgot to mention this. I followed the more or less standard > > > of 500 Hz bandwith. > > > > > > > There was an article in the RSGB magazine recently that said MDS is > not a > > substitute for NF (Noise Factor) but the concept of Minimum Detectable > > Signal seems easier to understand. > > I can make an approximate reading of the smallest signal I can > receive but > > how do I know what bandwidth I am looking at? > > I can do it by ear or by looking at a waterfall, I will get vastly > different > > results. By ear I may be using a 500Hz filter, by using a waterfall > I could > > be looking at a fraction of a Hz. > > Under what conditions are these measurements made? > > > > 73 Alan G4ZFQ > > > ------------------------------------ Yahoo! Groups Links (Yahoo! ID required) mailto:softrock40-fullfeat <mailto:[EMAIL PROTECTED]> [EMAIL PROTECTED]
