I guess the challenge would then be to be able to accurately attenuate the arb output down to a level similar to an HP346A or maybe just the HP346B. I'm sure it can be done but it will need some care.
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I've now got two more 346A noise sources here. Both were made in 2004 and both have current cal certificates from Keysight. I did a quick look on the Tek RSA3408A and they both look to be very similar to my 346A in terms of how much the noise rolls off below about 3MHz down to 1MHz. I'll do some more tests over the weekend.
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I tried again using 16 averages and got similar results. The manual suggests using 128 averages so maybe I'll try this over the weekend. The manual also suggests that the noise source should not be used for an hour before these tests such that it can thermally stabilise. I guess this means I don't handle them either as my hands will warm them up. So I'll have a fresh go over the weekend and try and follow the procedure in more detail.
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When I currently compare against either of the calibrated noise sources, I'm seeing a worst case ENR error of <0.03dB for my old noise source at 10MHz and 100MHz and 0.1dB at 1GHz. I've not tried the 2dB pad yet. I'm not expecting it to make much difference.
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Viadan, ok to e-mail privately and take this off-line? ?I would like to know more about what SP 9.1 -9.4 is measuring, and what it means. ? Good information on this entire thread. Gary WA2OMY ?
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From: [email protected] <[email protected]> On Behalf Of pianovt via groups.io
Sent: Wednesday, October 23, 2024 1:38 PM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] 346B verification?? Dave, it's actually not very complicated. Much of the document dwells on which buttons to push on the NFA. At its core, it's just a Y-method measurement. The formula also simplifies if you assume T=290K for the reference source and DUT. The OP didn't say much about his requirements, he may not even need ENR numbers above a GHz. People can get obsessed with these numbers, similar to reference standards for voltage, resistance, etc. However, there are other sources of error that can enter into NF measurements and overwhelm ENR uncertainty. Occasionally, I see people claiming NF measurements below 0.1dB with two digits precision. In truth, at best they can make relative measurements to compare competing designs, and only when measured with the same meter and same source. On Wed, Oct 23, 2024 at 08:03 AM, Dave Miller wrote: That looks like it will answer every question one could ever dream up. I naively thought it would be much easier?to do.
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My first attempt at comparing the two (calibrated by Keysight) 346A noise sources gave excellent results at 10MHz and 100MHz.
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I used an old Agilent E4440A PSA analyser with the built in noise figure personality to measure the Y factor but I used my own external preamp instead of the internal preamp in the E4440A. Note that my external preamp has a noise figure of about 2.8dB and a VSWR of <1.02:1 across 10-100MHz.
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Using the first 346A as ENR1 and Y1 I was able to predict the ENR of the second 346A to be within 0.01dB of what was stamped on it. This was a bit of a surprise, I didn't expect it to agree that well!
However, when tested at 1GHz, the prediction was off by 0.04dB but the VSWR of my preamp degrades to 1.15:1 at 1GHz. I could try again with a 2dB pad in front of the preamp but this will have to wait until later.
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When I tested my own 346A against one of the calibrated 346A noise sources I saw a worst case ENR error of 0.1dB. This isn't bad considering it hasn't been formally calibrated in about 20 years.
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All three 346A noise sources show excellent VSWR at these three test frequencies. They are all about the same. The plot below is the VSWR of my 346A up to 3GHz in both hot and cold states.
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I used the equation given in the N2002A manual to work out ENR2 from ENR1 and Y1 and Y2. It's probably best I repeat all this a few times to make sure I get consistent results. I'll use more averaging the next time although 4 averages seems to work quite well.
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I have an 8663A which uses similar but smaller adhesive feet as spacers on the power supply PCB. I believe to simply prevent the solder side of the board from touching the bottom cover.
It uses 3 or 4 of them and one of them (Only one) turned to mush as previously reported by the OP.? The others were seemingly unaffected in this way.? Can¡¯t think of a reasonable explanation in my case.
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Re: Added photo album Chemically Melted Rubber Insulation
#photo-notice
what is the mechanism that causes this?
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Dave, it's actually not very complicated. Much of the document dwells on which buttons to push on the NFA. At its core, it's just a Y-method measurement. The formula also simplifies if you assume T=290K for the reference source and DUT. The OP didn't say much about his requirements, he may not even need ENR numbers above a GHz.
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People can get obsessed with these numbers, similar to reference standards for voltage, resistance, etc. However, there are other sources of error that can enter into NF measurements and overwhelm ENR uncertainty. Occasionally, I see people claiming NF measurements below 0.1dB with two digits precision. In truth, at best they can make relative measurements to compare competing designs, and only when measured with the same meter and same source.
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Vladan
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On Wed, Oct 23, 2024 at 08:03 AM, Dave Miller wrote:
That looks like it will answer every question one could ever dream up.
I naively thought it would be much easier?to do.
Dave
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I think my focus was on the noise source itself, and assuming a non-defective attenuator would give better return loss. I wasn't thinking of the NFA itself and it's presumably non-reflectionless input with mixers and all that.
Thank you for encouraging me to dig deeper.
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Hello Chris,
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Nice to learn that.
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May be you are right as the two E3630A were stacked on the top a E3610 and both have the problem
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The E3610A itself was on a wooden table and the feet are perfect
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I have also two E3615A on the same table, not stacked, and the feet , only in contact with the table are also in good conditions.
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It seems that my problem is only on the feet which were in contact with the surface of another HP/Agilent power supply.
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Thanks for your detailled description.
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Best regards
Eric
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Look at the reverse isolation spec. Isolators or circulators offer low insertion loss and should offer > 20 dB of reverse isolation. This means that any reflected power ends up in the isolator and not in the circuit.? Mike
Hi Ed!
Easy one! IL low (<1 dB) S12 hi (> 20 dB). A pad might introduce too much loss, reducing the noise level too much, impacting measurement accuracy.
Jeff Kruth
In a message dated 10/23/2024 12:45:31 PM Eastern Standard Time, ed@... writes:
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How does one guarantee isolators are as good as good attenuators, other than to select with a VNA?
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Re: HP8555A BAND SWITCHING PROBLEM
Fixed. Not beautifully but efficiently I think.
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I first glued the parts together with cyanoacrylate to be able to work on them without risk. I don't think cyanoacrylate would keep so I "stitched" them with thin copper wire and added epoxy compound.
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Then when rebuilding I found that the previous suspect forgot to screw the SMA on the curved rigid to the N output.
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When I used it level was ok. Well, under 3 GHz at least...
Thanks again
Renaud
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Hi Ed!
Easy one! IL low (<1 dB) S12 hi (> 20 dB). A pad might introduce too much loss, reducing the noise level too much, impacting measurement accuracy.
Jeff Kruth
In a message dated 10/23/2024 12:45:31 PM Eastern Standard Time, ed@... writes:
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How does one guarantee isolators are as good as good attenuators, other than to select with a VNA?
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How does one guarantee isolators are as good as good attenuators, other than to select with a VNA?
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I think a lot depends on what frequency range you want to use the noise source over. If you plan to use it above a few GHz then sending it to Keysight (or Noisecom) is the only realistic option if you want reliable results. By reliable, I mean within reliably quoted uncertainty limits.
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If the upper frequency limit is less than 3GHz (especially less than 1GHz) then I think it can be done acceptably at home if you have access to the suitable test gear and a known good noise source to check against. This assumes that you aren't planning to use the noise source in a 'noise figure shootout' where you will be comparing your VHF or UHF LNA measurements in a competition for lowest noise figure etc.
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At work today I cherry picked two 346A noise sources that have current cal certs and I also took copies of the ENR tables from the latest cal certificates in each case. I picked the two with the lowest VSWR when measured on an E5080A VNA up to 9GHz. I'll try and cross check them against each other and against my old HP 346A up to about 3GHz. Obviously, I can't compete with Keysight here, but even a Keysight 'calibration' will have a degree of uncertainty and so will the noise source itself.
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If I was really fussed about this stuff I could have done this cross check numerous times since I bought the 346A many years ago. But I have never bothered because I think it is already close enough and stable enough to meet my needs up to about 3GHz. But I suppose it might be fun to try it anyway...
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Mine are all ok.? On that same power supply model and on others.
It's possible that you just got some bad LRFs (Little Rubber Feet) from the factory.? That can happen statistically.??
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____But the surface that they sit on makes a difference too!____
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Were your feet exposed to oils or any other organic solvents?? What about another type of rubber?
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One example from the lab at work:
We use the coiled wire ESD wrist straps in the lab along with the typical blue "rubber" ESD mat.
The straps that were kept in a (metal) drawer are fine.? All of them are fine with no signs of damage.
But the ones that were left one the bench in contact with the blue mat for a long time are breaking down.
The same straps, purchased at the same time, from the same MFG lot.
The only difference is contact with a metal drawer vs. contact with the rubber ESD mat.
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The cables that were in contac twith the ESD mat show 2 failure modes.
On some of the straps, the wire insulation exhibits the typical rubber surface breakdown with white powder that you can rub it off with your hand.??
On other straps, the wire insulation and the ESD mat co-melt each other.? Thats a really weird reaction!
But It's exactly the kind of thing I've seen on LRFs that sat on a rubber mat for a long time.
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I've uploaded a photo.? Search the phtotos section for "Chemically Melted Rubber Insulation".
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The bottom cable shows the typical chalky sruface break down.??The top cable shows the chemical melting from being in contact with the ESD mat.
If you zoom in on the top cable (near the blue crimp connector) you can see the insulation is completely rotted and melted away from the wire.
The blue goo is the product of the wire insulation and the mat co-melting each other.? It is a still a permanent liquid after many years.
(yes, that bench has never been cleaned)
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I first assumed that the goo was blue from the copper in the wire, but I think it's actually from the ESD mat because the mat has clearly been melted by contact with the cable.
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Added photo album Chemically Melted Rubber Insulation
#photo-notice
Chris Wilkson <cwilkson@...> added the photo album
Chemically Melted Rubber Insulation
: Photo showing 2 types of rubber insulation break down when stored on a typical blue rubber ESD mat.
One break down mode is a typical chalky white powder on the surface of the insulation, easily removed.
The other break down mode is a liquification of the black rubber insulation *and* the blue ESD mat that it was sitting on (and above, but not in contact). The liquid is quite viscous (similar to honey) and this state is permanent.
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Hi Vladan, Thank you very much, That looks like it will answer every question one could ever dream up. I naively thought it would be much easier?to do. Dave VE7HR
Hi Dave,
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Look for this document:
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Keysight N2002A Noise Source Test Set
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Chapter 3 has the manual measurement procedure. The instructions are for the NFA, but the concept is the same if you use an 8970. Same formula.
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Vladan
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At Keysight, the noise source measurement bench uses two noise sources to calibrate the customer's noise source.
And of course the measuring bench in question includes the isolators as on the N2002A in order to guarantee the best possible accuracy.
For me and for many of the experts in this field, as VSWR is the biggest contributor to uncertainties in noise measurements, it is obvious that calibration without isolators is absolutely impossible. This can only be a check of proper operation, but in no way can this be called a calibration.
Even if it means paying, you might as well pay to get the most accurate values as possible.
Obviously Noisecom is certainly as precise as Keysight but I strongly advise against any other provider that is not seriously accredited. To determine which is the best, it is sufficient to request the technical annex of the accreditation in the field of noise measurements from the testing laboratory and to check whether the calibration uncertainties are satisfactory or not.
If the lab isn't accredited, then drop it, you'll pay for nothing.
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Re: Agilent Logic Analyzers 90-pin connectors
Wasn't Digihouser a television show? DaveD KC0WJN
Thanks for all the fish.
============================== All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994) ==============================
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On Oct 23, 2024, at 04:29, Christian F1GWR via groups.io <f1gwr.groups@...> wrote:
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I love "Mousikey"
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Hello Renaud,
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There's obviously their brothers: Digouser.
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73,
Christian
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M. et Mme p'tite'pip ont trois filles :
- Anne
- Justine
- Corinne
Comprendra qui pourra...
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Eric, Glad my input helped! Once replaced, those will work as designed (non-slip, elevating the unit off the shelf for some convection, etc.) for a very long time (probably longer than the original due to likely better chemistry of the rubber today),?essentially equivalent to the original ones.? Radu.?
Thanks Radu !
Following you message , I went to the Anchor Electronics web site and I have discovered the words "Square base (tapered) bumper" as in fact I was searching on the web with "square feet"
So then ,I found the 3M Grey Bumpon SJ5023? which seems the right one and available from Mouser at a good price
Thanks again
Best regards
Eric
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RFI-EMI-GUY