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Look, here's a simple example. I have an HP8566B analyser here and it's noise figure is typically 24dB. i.e. the noise floor is -150dBm/Hz. If I place a 27MHz amplifier ahead of it with about 16dB gain and a 5dB noise figure and try to measure the noise figure of the amplfier the...

Which bit of "noise is not a continuous wave signal" don't you understand? You keep posting up quotes from parts of the pdf that relate to S/N vs RBW for continuous wave signals? YOU ARE READING THE WRONG SECTION. Read the section on measuring NOISE. i.e. when external NOISE is the...

Here's some basic physics about the nature of noise. Thermal noise power can be measured using noise power = kTB . T = temperature = Kelvin = 290K at room temperature k = Boltzmann's constant = 1.38 E-23 J/K B = Noise Bandwidth (Hz) So if you change the detection bandwidth B by a...

The stuff you posted in your latest post is still all related to detecting CONTINUOUS WAVE signals. Noise is not a continuous wave signal! It is random in nature :) Sorry if you couldn't find the text I quoted. I posted up a link to a more modern version of application note AN-150 in...

It's in pretty much every HP application note on this subject dating back about 40 years. Eg it's even in the old 1974 article you linked me to earlier :) http://cp.literature.agilent.com/litweb/pdf/5952-0292.pdf Look at the section on noise measurements eg the text below is on page 10 of...

If I made the measurement I would expect it to equate back to a noise floor at the input of about -165dBm/Hz. I always use the 1Hz noise marker function because it corrects for the detector and log amp errors and also the noise bandwidth of whatever RBW I have selected. Otherwise I have to...

Like I keep telling you, the benefits of the narrow RBW apply to small continuous wave signals, eg a steady carrier that can sit inside the 10Hz RBW. Noise isn't a continuous wave signal. So reducing the RBW offers no benefit when measuring noise power. Yes it does that on mine too. But...

I do it using a sig gen at the input and a true rms voltmeter at the AF output and for a healthy mk2 Cobra 148GTL-DX I'd expec the noise floor in a typical SSB bandwidth of 2400Hz to be about -131dBm in SSB mode. (= -165dBm/Hz noise floor) I can also use a NoiseCOM noise source to measure the...

But you can't dodge the 24dB noise figure limitation of the analyser when you are trying to measure NOISE levels. We can agree that kTB noise in a 1Hz bandwidth at room temperature is -174dBm/Hz. So.... if an analyser has a 24dB noise figure at 27MHz then it can be modelled as a receiver...

Yes, if you select 10Hz BW this is true for discrete and narrow signals that are less than 10Hz wide but you are in the business of measuring noise levels so going down to 10Hz RBW doesn't make the analyser more capable in terms of measuring low noise levels. eg if I inject a 24dB ENR (Excess...

I see you just added the above text as I posted my last reply... The above methods are a LOT better and I think you will get much more meaningful results :) The reason I think your analyser has a 24dB noise figure is because: kTB noise is -174dBm/Hz 10Hz is 10dBHz noise floor quoted...

Assuming your 8553 is unmodified then we can agree the fact below between us: The -140dBm sensitivity in a 10Hz BW equates to a receiver (analyser) noise figure of 24dB. i.e. it has a very deaf receiver compared to a CB radio. If we can agree your analyser has a NF of 24dB then if you...

OK I looked up the 8553 manual and it suggests your analyser has a 24dB noise figure. So this will make it very difficult to see a small improvement in NF of the first amplifier stage in your CB radio unless you add a preamp in front of the 8553. Why not punch some numbers into a gain/noise...

To be fair the true rms meter suggestion was against your previous (flawed) test method where you wanted to couple the analyser direct to the collector of the 2SC1730. This flawed method will load the 2SC1730 circuit in an unnatural way. Also your 8553 on its own won't be sensitive enough to...

Yes, I think you tuned it the best way :) I think Uniden 'tried' to include something about how to do this 'flatter tuning' in the service manuals for some Uniden export CBs. However, I believe the instructions got corrupted in the Uniden document either due to typing errors or translation...

Glad it was useful :) The last time I looked (months ago) it only had a few views so it's nice to get some feedback :)

Thanks for the link to the old HP document but I'm already very familiar with how to use a spectrum analyser to measure noise figure as I've done this many times both at my place of work and here at home :) Note that I'm not saying your test method isn't scientific 'because' you are using a...

Rather than just change all the caps, why not simply check them out with an ESR meter? You can usually spot a failing cap with an ESR meter before it goes really bad. The worry about buying caps in bulk to replace all the ones in the radio is that you could be replacing the original with a...

Well it's interesting that people still are interested in doing the 2SC2999 swap... :) Hi KG6, Your test method with the analyser isn't particularly scientific because you will load the circuit at TP13 with the analyser and also the signal you see at TP13 will be affected by AGC action when...

In case anyone is a bit mystified why the AGC causes the noise it's because of where the AGC takes place and because of the gain distribution in the radio. Basically the WORST place to put ALL of the AGC would be at the very front of the radio. This is because the signal would always be tiny...