How to perform the 2sc2999 and Schottky diode swap

[G0HZU]

This text is directly out of the same AP note, so is in direct conflict with your position.
Resolution bandwidth also affects signal-to-noise ratio, or sensitivity.

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 signal of interest. (Not the earlier section where a carrier or FM signal is the signal of interest)

To measure the noise figure of the first RF amplifier at TP13 you have to be able to measure the levels of the NOISE. But this noise level will be too close to the noise level of the analyser because it has a 24dB noise figure. i.e. it is too DEAF. Changing RBW down to 10Hz will not help here because you need to measure noise (not a continuous wave signal)

The ability to measure this noise is the limiting factor and it is limited by the 24dB noise figure of the analyser.


Why do you think all the articles written by HP put a PREAMP in front of the analyser? They even give worked examples to show you the benefit of the preamp.

If we examine what happens as the spectrum analyzer bandwidth is changed, we will see that the sensitivity for random noise measurements is independent of bandwidth.
For example, we narrow the bandwidth by a factor of 10. The analyzer's internal noise (which is, itself, random noise) is decreased by a factor of 10, or 10 dB. At the same time, the random noise we are measuring also decreases by 10 dB, so the signal-to-noise ratio remains constant.

Which bit of this quote from Hewlett Packard do you not understand?

Are you saying they are wrong too?

It is referring to S/N where the signal of interest is NOISE. i.e. if you are trying to measure the NOISE level from a test amplifier.

Please, PLEASE don't keep quoting from the section about CONTINUOUS WAVE signals. Noise is different. It is random. There is no benefit in system sensitivity by going to a narrower RBW when you are trying to measure external noise.

I have posted up this as a FACT written by Hewlett Packard. All you seem capable of doing is quoting up info from the WRONG SECTION of their documents to try and prove Hewlett Packard (and modern physics and myself) wrong.


One final time:

By Hewlett Packard:
we will see that the sensitivity for random noise measurements is independent of bandwidth.....

we will see that the sensitivity for random noise measurements is independent of bandwidth.....

we will see that the sensitivity for random noise measurements is independent of bandwidth.....

we will see that the sensitivity for random noise measurements is independent of bandwidth.....

we will see that the sensitivity for random noise measurements is independent of bandwidth.....

we will see that the sensitivity for random noise measurements is independent of bandwidth.....

Try and accept this and then we can all go home...

 

[G0HZU]

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 analyser will get it wrong. This is similar to your proposed test at the first RF amplifier at TP13.

This is because the noise produced by the amplifier (gain plus noise figure) will be 3dB below the noise level of the analyser. i.e. the amplifier will churn out noise at

-174 +15+6 = -153dBm/Hz.


Therefore the analyser will make the amplifier look noisier than it really is because the internal noise of the analyser will mask the (lower) noise of the amplifier.

It doesn't matter if I use 10Hz RBW, 100Hz RBW or 1kHz RBW this noise will always be 3dB below the noise floor of the analyser and it will get the result equally wrong in every case assuming the RBW filters are ideally calibrated and corrected for making noise measurements.

Analyser noise floor..................Amplifier Noise output

-110dBm/10kHz ...................-113dBm/10kHz
-120dBm/1000Hz..................-123dBm/1000Hz
-130dBm/100Hz....................-133dBm/100Hz
-140dBm/10Hz......................-143dBm/10Hz
-150dBm/1Hz........................-153dBm/1Hz

Can you not see that the -3dB problem is still there even with the 10Hz RBW?
i.e. changing to a narrower RBW achieves NOTHING when trying to measure the noise output from the amplifier. It will still get the result wrong and will make the amplifier look noisier than it really is.

By Hewlett Packard:
we will see that the sensitivity for random noise measurements is independent of bandwidth.....
we will see that the sensitivity for random noise measurements is independent of bandwidth.....

 

[KG6YGE]

No it won't...think about this scenario-no inline preamp with a lower NF used.

Hypothetical carrier measured at peak - 0 dBm (1 mW). Perfect ideal carrier with no bandwidth. The ideal case. All carriers have some BW, the case is still valid.

Adjacent noise floor (per unit hertz) is 60 dB down. Which is 1 millionth of a milliwatt per unit hertz. This noise floor extends to the edges of our scanwidth.

Carrier to noise ratio is 60dB in a 1 hertz BW.

Now, lets raise the noise floor 3dB due to changing the res BW (KTB with larger BW by a factor of 2 in the IF chain). Now we have 1/500,000 of a milliwatt per unit hertz at the noise level. Since the noise is uniformly spread, it adds to the carrier power at the carrier frequency too. But 1/500,000th of a milliwatt is so small a fraction of 1 mW that there is no change to the carrier power to speak of. The carrier didn't go up 3dB with the noise floor.

Is that the confusion between us (which the rest of the board may not care about)?

I have nothing against inline series low NF preamps per say, since they lower the net NF of the whole measurement chain. Thats why people where changing the RF amp with the 2SC2999E, agreed ?

 

[G0HZU]

The carrier didn't go up 3dB with the noise floor.

I know it won't go up 3dB. I'm not saying it will The carrier is a continuous wave signal rather than noise. You aren't proving anything relevant with your latest example?

What you are overlooking is that in order to assess the noise performance of an amplifier stage you have to measure the NOISE level from it at some point.

You keep arguing (and quoting) the RBW vs sensitivity case for measuring a carrier. It isn't relevant. You don't 'need' to measure a carrier signal in order to measure the noise figure of an amplifier.

But you do need to measure noise power at least once

When you measure that noise from an amplifier then there is no benefit to using a very narrow RBW to measure the noise as it won't enhance the sensitivity when measuring NOISE.

According to Hewlett Packard:
we will see that the sensitivity for random noise measurements is independent of bandwidth.....

If you disagree with this quote from HP then you are disagreeing with modern physics and (hopefully) every RF engineer on the planet

 

[KG6YGE]

Here's more context on App Note 150 to round out the discussion on noise power and noise figure, and how to measure the NF of the SA-


"At room temperature and for a l-Hz bandwidth, kTB = -174 dBm. We know that the displayed level of noise on the analyzer changes with bandwidth. So all we need to do to determine the noise figure of our spectrum analyzer is to measure the noise power in some bandwidth, calculate the noise power that we would have measured
in a l-Hz bandwidth using lO*log(bwJbw,), and compare that to -174 dBm. For example, if we measured -110 dBm in a lo-kHz
resolution bandwidth, we would get

NF = (measured noise),m,, - l0*log(RBW/l) - kTB,_
= -110 dBm - 10*1og(10,000/1) - (-174 dBm)
= -110 - 40 + 174
= 24 dB.
Noise figure is independent of bandwidth."


Noise Figure is a function of device temperature and current flow. So there are three terms that define how much noise power is within a channel, K, T, and B. They are all physically independent parameters, and aren't correleated.

I have a good idea for us.

Measure with your 8566 the noise floor of your Cobra 148 radio, just before the detector diodes at the end of the I/F chain. Set the scan width to be 10 KHz total, and measure the peak noise at channel center.

Make the measurement with the radio off, and then turned on, with the antenna input terminated. No signal, RF gain at max CW, then post your results.

 

[G0HZU]

I've got a much better idea....

Why don't you tell me if you still think my statement below about measuring noise is WRONG.

This is what started the whole debate.

G0HZU: 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.

KG6YGE:Wrong on that.

Please bear in mind that I have modern physics on my side and also I can quote from HP to back up the above statement.

By Hewlett Packard:
we will see that the sensitivity for random noise measurements is independent of bandwidth.....

So do you retract your statement that I was wrong?

Or do you think that HP are wrong as well as me?


Look!

Noise figure is independent of bandwidth

You have even (correctly) quoted this above so why can't you now understand that the sensitivity to NOISE for your analyser is determined by the NOISE FIGURE of the analyser and you can't use RBW to overcome this limitation.

I'm yet to find an american radio ham on any forum who will admit he was wrong about anything so I won't hold my breath...

 

[AudioShockwav]

I'm yet to find an american radio ham on any forum who will admit he was wrong about anything so I won't hold my breath..

Hey, I have admitted I have been wrong at least once in my lifetime,
I dialed a wrong phone number one time........

73
Jeff

 

[Mudfoot]

I've admitted my stupidity and ignorance on several occasions.

Must be because my grandparents immigrated from Great Britain. Why they settled in West Virginia is still a mystery.

I'm part English Hillbilly. And proud of it!

 

[The Mad Scientist]

:laugh:

 

[Abikerlad]

Super thread saved me the time and money on this.

What a great thread, super advice from the G0 call saved me going down the route of spending cash for nothing to be gained.

 

[Robb]

What a great thread, super advice from the G0 call saved me going down the route of spending cash for nothing to be gained.

Using the 2999e transistor mod is a crap shoot; some radios clearly do not need it. In others, it works OK.

But the 1N6263 Shottky diode mods for receive and the noise blanket circuits are definitely OK to use in most radios.
You can do that much with no problems or questions.

 

[KG6YGE]

I made the swap today, using a Sanyo 2SC2999-D. Has about the same Hfe range as the original 2SC1730L, but lower noise figure. Have not changed the detector diodes. The 2SC2999E is hard to find.

On the generator, had a couple more dB C/N at 7.8 Mhz, and picked up 1/2 an S meter reading, from 8 to 8.5.

Initial results are more sensitive on AM (CB), picking up noticeably better voice articulation than the TRC 433, after a couple of hour comparison. Very pleased with the AM improvement.

As far as SSB, right now CH 38 is very quiet, just a couple of people talking, no location given.

Update- # Worldwide Radio 0527-the voice of Jamaica, is coming in very clear now. He's also contacting Barbados and Cuba. This is at 16:20 EDT. This guy is coming in over the top of #2966 San Diego.

 

[Klondike Mike]

... The 2SC2999E is hard to find.

I rec'd a few 2SC2999E's from Consolidated Electronics last week. 25c/piece. HFE ranged from 100-130 whereas a few "D's" I have ranged from 80-100.

http://www.ceitron.com/cart/

 

[KG6YGE]

Well, I'm convinced this was a good modification to make, at least with the 'D' version. The TRC 458 was always great on SSB, getting good reception to the western US and Europe, depending on time of day, but not quite as good as the TRC 433 base in side to side comparisons on local (-200 mile AM). I would say they were almost equal in AM mode, but not quite. Now, the 458 with the 2sc2999-D is clearly better than the 433 (stock), and I didn't adjust anything. I do plan on checking against my baseline set of pre-mod #s again to see if the numbers reflect the improvement in audio and sensititity.

 

[godcobra]

MGF1302-15 Mitsubishi

you want to see a real difference try this transistor MGF1302-15 Mitsubishi let me know what you tink I put that in my hr2519 and galaxy 88hl and bang I got new radio in my hand