Re: HP8555A BAND SWITCHING PROBLEM
Thanks Ed,
There's not much room to add matter around unfortunately. I even had to remove some epoxy to allow enough free movement.
Epoxy seems happy to adhere well to that plastic. Robert suggested a probably better glue but I wanted to fix that fast because the dismantling was complex and I was worried I would not remember how to rebuild.
And, yes, I glued the spring at it's base too. It pushes a steel pin inside the ratchet end of the drum. Hope my english make sense here!
Best
Renaud
|
HP 8510C floppy drive replacement
Hi,
I found the floppy drive on my 8510C VNA was dead when I tried to save Calibration info to a floppy disc. When I initialized a 1.44mb floppy disc, it ran about 50 tracks and aborted, complaining write error.
?
Is the 8510C picky about what brand, model of floppy drive? Can I just get a good one of any brand?
?
Regards,
Calvin
|
Let me second the suggestion for the 3M BumpOn family. As we would say
in Austria, Ehrenprodukt.
My African-American client and I have hundreds of them in the field and
are most satisfied, often even in challenging environments and
surrounded by intellectually challenged operators.
Incidentially, once you buy more than say 10k pieces, the OEM can be
found via Google. They are in the USA and are willing to talk with you,
but only at 10k units or so.
Tam
With best regards
Tam HANNA
--
Enjoy electronics, 3D printing and cigars? Join more than 21000 followers on my Instagram at
|
Re: HP8555A BAND SWITCHING PROBLEM
Great job, and nice that you got the wire loops all the way around, so both directions of lever action are reinforced. I would only suggest maybe adding some epoxy fillet to that flat section opposite the outside lever, to join with the hub and the arm that reaches outward to actuate the ratchet mechanism on the drum, and with the bead of epoxy you already placed. And the same on the other side, between the flat and the hub. That all would help with the torque that tends to deform the whole thing and twist the arm.
?
Note the small gusset between the arm and the end cylinder for reinforcement against forces on the pin that goes in there. So, it was designed with some consideration of reinforcement, but that arm joint is a sharp inside corner, which adds lots of stress there, which appears to be where it began to tear loose in the first place. It may be good to also epoxy up at least the base of that metal spring thing on the side where it's attached with the molten pegs. I can't tell what that's for, but it looks to me like it's for axial load on the pin that goes in the end cylinder. Is that pin supposed to move? You should figure out what it's for before sticking anything on there, but if it's non-critical, you can add a little strength there too.
?
I don't know what type of plastic it is, maybe an alloy, and possibly glass-filled, which should be stronger than regular, but everything still has its limit. To get a better bond with the epoxy, it's good to roughen up the surfaces first, and wash it with IPA. Be generous with any epoxy added, while of course not overdoing it and interfering with anything.
?
Ed
|
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.
?
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.
|
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.
?
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.
?
?
|
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 ?
toggle quoted message
Show quoted text
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.
|
My first attempt at comparing the two (calibrated by Keysight) 346A noise sources gave excellent results at 10MHz and 100MHz.
?
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.
?
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.
?
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.
?
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.
?
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.
?
?
?
|
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.
|
Re: Added photo album Chemically Melted Rubber Insulation
#photo-notice
what is the mechanism that causes this?
|
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.
?
Vladan
?
?
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
|
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.
|
Hello Chris,
?
Nice to learn that.
?
May be you are right as the two E3630A were stacked on the top a E3610 and both have the problem
?
The E3610A itself was on a wooden table and the feet are perfect
?
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.
?
It seems that my problem is only on the feet which were in contact with the surface of another HP/Agilent power supply.
?
Thanks for your detailled description.
?
Best regards
Eric
?
?
|
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:
?
How does one guarantee isolators are as good as good attenuators, other than to select with a VNA?
|
Re: HP8555A BAND SWITCHING PROBLEM
Fixed. Not beautifully but efficiently I think.
?
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.
?
Then when rebuilding I found that the previous suspect forgot to screw the SMA on the curved rigid to the N output.
?
?
When I used it level was ok. Well, under 3 GHz at least...
Thanks again
Renaud
?
|
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:
?
How does one guarantee isolators are as good as good attenuators, other than to select with a VNA?
|
How does one guarantee isolators are as good as good attenuators, other than to select with a VNA?
|
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.
?
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.
?
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.
?
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...
?
?
|
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.??
?
____But the surface that they sit on makes a difference too!____
?
Were your feet exposed to oils or any other organic solvents?? What about another type of rubber?
?
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.
?
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.
?
I've uploaded a photo.? Search the phtotos section for "Chemically Melted Rubber Insulation".
?
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)
?
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.
?
|
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.
|
RFI-EMI-GUY