Re: HP8757A Display Problem (Scalar Network Analyzer)
Isn't the 1345A the smaller ~5" version used in eg. 3577VNA?
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Ulf
SM6GXV
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Re: (OT?...) Sticky labels for aluminum and other typical materials panels
When discussing P-Touch labels, bear in mind that M-type machines are a thermal ink process and TZ-type machines use a thermal transfer process that is self-laminating.?
M-type is substantially more prone to fading than TZ.?
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On May 18, 2025, at 02:25, Mark Moulding <mark@...> wrote:
? That's actually , and I think they're great - I use them quite a bit.? They have their own specialty CAD package to design a front panel, which is extremely easy to use.? As you add features (engraved lettering, corner radiusing, round or square holes, stand-offs, etc.), you can click a button at any time to find out how much the panel will cost.? For what you get, the prices are pretty reasonable,considering that what you get are extremely first class panels.? They do the paint back-fill oepration, plus you can have the panel powder-coated.? I've attached a picture of a half-sized HP 2100 computer I've been building - I think it turned out pretty well...
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Mark
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Hi Group,
My E4407B has the problem of 'LO unlock'. I am in the process of repairing the unit by replacing a frequency divider. I am following the youtube video in the SignalPath channel. Before replacing the component I would like to check the rest of the system as much as possible. The problem is that I cannot find the schematics for the unit. It is not part of the service's manual. I would like to know if somebody could help me with this.
Regards, David. -- David Rodriguez Callsign: M0KGE Location: Cambridge, UK
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Re: 1 mw - 0dbm lab calibration
Hi Harke, thanks!
It's interesting to see the return loss plot of the 8478B sensor out to 3 GHz.
I've started a thread about the input return loss of the 478A sensors and how they have changed internally over the years.
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Regards
Jeremy
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Re: HP 478A Thermistor Sensor. Input return loss and matching
The other thing to bear in mind is that the latest 478A service manual clearly shows that all versions of the standard 478A sensor (note that this doesn't include H7x options) can be used with both the 431 and 432 power meters. So I don't think the RC damper is essential for the 431 power meter as the service manual shows the 431 being used with the later 478A sensor that has the ferrite but no 2.7R + 460pF RC damper network.
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Also, the reactance of a 460pF capacitor at 10kHz is about -35,000 ohms so there seems little point putting a 2.7R resistor inline with such a high reactance at 10kHz. So I'm not convinced this RC network in the early 478A sensor type is a necessary requirement for the 431 power meter operation with its 10kHz bias system.
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Regards
Jeremy
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Re: HP 478A Thermistor Sensor. Input return loss and matching
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Just to keep things in perspective, the input VSWR will be a function of the design of the 478A sensor and will also be affected by the performance of the 432A power meter to some degree. However, if a healthy 432A power meter is used and a typical 478A sensor is used that has the same blocking caps shown in the service manual then I think that the input VSWR at 50 MHz is typically going to be about 1.07:1 at 50 MHz.
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Mine has been 1.07:1 for over 30 years for example. The source VSWR of a typical HP 1mW reference (50 MHz) is spec'd to be better than 1.06:1 and I would expect it to be a bit better than this in reality. The mismatch uncertainty between 1.07:1 and 1.06:1 is about +/- 0.01dB. I've done load pull testing on my Anritsu 1mW source that suggest it has a VSWR much lower than 1.06:1 and in this case the mismatch uncertainty falls below +/- 0.01dB.
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However, if lots of 1mW references were being measured and they had a spread in source VSWR that covered all phase angles of a 1.06:1 VSWR then this could cause some spread in results for someone trying to get repeatable results below about +/- 0.01dB using DC substitution when comparing a H72 sensor against a standard 478A sensor. But I'd argue that the drift caused by handling the 478A sensor would cause similar spreads unless some time and care was taken when doing the comparisons.
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In theory at least, adding the matching section would minimise the spread seen with the standard sensor but I'm not sure it is really that worthwhile to chase down errors in the ballpark of +/- 0.01dB unless this is being done at a decent calibration/metrology lab.
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Regards
Jeremy
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Re: HP8757A Display Problem (Scalar Network Analyzer)
Philip, I thank you for the information; yes it may be that we were typing at the same time! I shall look further this morning and see what I find.
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Re: (OT?...) Sticky labels for aluminum and other typical materials panels
That's actually , and I think they're great - I use them quite a bit.? They have their own specialty CAD package to design a front panel, which is extremely easy to use.? As you add features (engraved lettering, corner radiusing, round or square holes, stand-offs, etc.), you can click a button at any time to find out how much the panel will cost.? For what you get, the prices are pretty reasonable,considering that what you get are extremely first class panels.? They do the paint back-fill oepration, plus you can have the panel powder-coated.? I've attached a picture of a half-sized HP 2100 computer I've been building - I think it turned out pretty well...
~~
Mark
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Re: Looking for service manual/schematic for early E3611A DC Power Supply
Thanks for all the info!
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Unfortunately, none of those schematics match the layout in my instrument. For example, the PCB I have has no C20 (connected to pins 2 and 3 of U4), or any provision for C20 to be fitted.
A few resistors in my instrument are different values too, as are all the opamp part numbers.
I also have an R21, that doesn't seem to exist on the schematics as well.
I found the following resistors are different values:
R14 is 33R instead of 1K
R15 is 8.45K instead of 6.19K
R28 is 8.2K instead of 6.81K
R33 is 6.19K instead of 5.23K
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I also found the current pot was only a single turn (factory fitted) so I replaced it with a 10 turn pot. I think it was the same value but it was so long ago that I can't remember.
Also the output binding posts were red/red/black instead of red/black/green (for +ve/-ve/GND) so I changed the colours, but that would have no affect on the operation.
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I'm not sure what is up with this instrument, but I am pretty sure that I am the first one inside as far as I can tell, as I replaced the original leaking capacitors, and the solder joints look untouched (until I replaced caps etc).
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I'm having a problem where all the functions appear to work, except when pressing the Current Set button, where the display shows between multiple amps across the range of the current control, which is far too high for the instrument to be capable of.
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I'm thinking of just changing the resistors to match the schematic, to see if that will pull things into line.
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Re: HP 478A Thermistor Sensor. Input return loss and matching
In case any purists want to scoff at this matching technique and think it is a bodge, I suggest they take a look inside a typical HP power meter and look at how the 1mW oscillator is designed and how it achieves its output match. It uses a tiny series inductor to cancel out the capacitance of the capacitive divider used at the output of the oscillator. This ideally leaves a pure (series) 50 ohm source impedance at 50 MHz. This is how HP tried to get a very low source VSWR for their 1mW source at 50 MHz.
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Obviously, it's a good idea to try and trim the tiny inductance to be spot on and that is what I have done here in order to get a really low VSWR at 50 MHz.
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If it's good enough for HP then it's good enough for me :)
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Regards
Jeremy
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Re: HP 478A Thermistor Sensor. Input return loss and matching
On Sat, 17 May 2025, jmr via groups.io wrote: There are separate manuals for all those Hxx 478A sensors. There was a whole bunch of those, all seem to be nearly identical according to their manuals. H55 -- 00478-90029 H63 -- 00478-90030 H72 -- 00478-90031 H73 -- 00478-90032 H75 -- 00478-90033 H13 -- 00478-90036 They all use 0.1uF capacitors. There was also a 8478B option H01 with the same specs. No manual for that, just a product note telling it has a VSVR of 1.05 or less at 50MHz. And here is kinda addendum from HP (before Agilent/Keysight) for H75 that they suggest using along with original 478A 00478-90021 manual (attached, hopefully it will get through). Just to clarify, the latest service manual for the standard 478A sensor is available on the Keysight website and this lists the different internal circuits for the early and later variants of the standard sensor (as I have posted on this thread) and it provides a serial number checker in the appendix. This is how I know my sealed and unused sensor is one of the later types with a ferrite bead. It has a serial number greater than 65601 so the B changes in the manual apply to this sensor.
My early 478A sensor was probably made in the mid 1960s so it has the RC damper in it and no ferrite bead.
Note that this service manual doesn't cater for the H7x variants that use 0.1uF caps. My aim in this thread is to see how well I can improve the input VSWR of an early (or late) standard 478A sensor so it has a similar or better VSWR at 50 MHz compared to the H7x variants.
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Regards
Jeremy --- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
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Re: HP 478A Thermistor Sensor. Input return loss and matching
Here's a screenshot from my old Agilent VNA showing the input VSWR of my 478A sensor with the matching section added at the input. You can see that it now achieves a really low VSWR at 50 MHz.
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Because I've used low loss parts, there is no through loss penalty when the matcher is inline. This is because the approx 0.004dB mismatch loss caused by the capacitive input of the standard sensor is made up for by having the series matching inductor inline. However, due to the finite Q of the matching inductor the model predicts that there will be about a 0.004dB loss caused by the matching inductor. So the two cancel out. So when I next check my 1mW source from my power meter, I can do it with a 478A sensor that has very low input VSWR. Probably as low as the VSWR of the H7x variants at 50 MHz.?
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I don't need to worry about harmonics because the harmonic distortion levels from the 1mW source are very low. Better than -60dBc.
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Regards
Jeremy
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Re: HP 478A Thermistor Sensor. Input return loss and matching
On Sat, 17 May 2025, jmr via groups.io wrote: H72 is SPECIFICALLY designed for low frequency measurements, especially that 50MHz one. It is not high frequency device going into gigahertz range so it didn't require tiny special microwave capacitors with low inductance. All other 478A (except similar H75/H76, maybe some other Hxx) on the other hand are totally unsuitable for that 50MHz (and general low frequency) measurements. Those Hxx are special calibration devices, not general purpose power sensors. OK thanks. I think the standard 478A sensor uses a tiny (and very thin) SMD disc cap of about 1350pF for the AC ground end of the thermistor. The later 478A sensor uses 1200pF here.? I don't know what package type is used for the series blocking cap at the input.
Because the sensor is designed for use to 10 GHz I think this capacitor will have relatively low package inductance compared to a regular MLCC in a 1206 package.
I'm not sure what package the 0.1uF caps use in the H72 but if they are allowed to be as large as a 1206 MLCC then maybe a MLCC with a class 1 COG dielectric can be used here. This might help explain why the upper frequency range is much lower for the H72 version.
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Regards
Jeremy --- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
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Re: HP 478A Thermistor Sensor. Input return loss and matching
Just to clarify, the latest service manual for the standard 478A sensor is available on the Keysight website and this lists the different internal circuits for the early and later variants of the standard sensor (as I have posted on this thread) and it provides a serial number checker in the appendix. This is how I know my sealed and unused sensor is one of the later types with a ferrite bead. It has a serial number greater than 65601 so the B changes in the manual apply to this sensor.
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My early 478A sensor was probably made in the mid 1960s so it has the RC damper in it and no ferrite bead.?
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Note that this service manual doesn't cater for the H7x variants that use 0.1uF caps. My aim in this thread is to see how well I can improve the input VSWR of an early (or late) standard 478A sensor so it has a similar or better VSWR at 50 MHz compared to the H7x variants.
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Regards
Jeremy
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Re: HP 478A Thermistor Sensor. Input return loss and matching
OK thanks. I think the standard 478A sensor uses a tiny (and very thin) SMD disc cap of about 1350pF for the AC ground end of the thermistor. The later 478A sensor uses 1200pF here.? I don't know what package type is used for the series blocking cap at the input.
Because the sensor is designed for use to 10 GHz I think this capacitor will have relatively low package inductance compared to a regular MLCC in a 1206 package.
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I'm not sure what package the 0.1uF caps use in the H72 but if they are allowed to be as large as a 1206 MLCC then maybe a MLCC with a class 1 COG dielectric can be used here. This might help explain why the upper frequency range is much lower for the H72 version.
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Regards
Jeremy
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Hi Joe,
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If you just change some parts without knowing why you only make it worse. You give exact 0 information what was your error-picture, what you did or what voltages did you measure. My advice:
print out the schematc, mark the GND reference against which there is the masurement. If you measure, take the DC and AC Voltages and write them in the schematic. Check all voltages from left to right. Only C10, C12 or C14 may have up to 0,1V AC without load.
There may be a defect capacitor. But defect diodes or transistors are more common.
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before you open the device: unplug it. If open: Isolate ALL life points, no exception. Use an isolation transformer.
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Are the bridges on the rear according to the schematic?
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Roland
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Re: HP 478A Thermistor Sensor. Input return loss and matching
On Sat, 17 May 2025, jmr via groups.io wrote: There are 0.1uF C0G capacitors in 1206, nothing special. I have a reel of those and use them often. Dunno what capacitors are inside H72 probe although I have one here. Judging from the head external dimensions I don't see any problems fitting a couple of 1206 capacitors in there. I'd expect the 0.1uF caps in the H72 sensor to be class 2 ceramic types as it's hard to imagine COG/NP0 being used here. This would presumably make the reactance at 10kHz susceptible to temperature changes and this might also worsen the drift vs temperature if you tried to use it with a 431 meter. So there's probably more than one reason the H72 can't be used with the 431 meter.
I'm not sure how stable the ESR of the 0.1uF caps will be over temperature up at 50 MHz but presumably these caps were chosen carefully by HP. The ESR of these caps will contribute to the efficiency factor stamped on the sensor as the ESR in these caps will rob a tiny amount of the incident power to the thermistor. However, the ESR will probably be tiny at 50 MHz. The ESR will increase up towards 1 GHz and this will cause some loss in efficiency as the ESR of class 2 ceramic caps does tend to climb rapidly up in the GHz range.
The standard sensor will use thermally stable caps here with low ESR and I would expect the loss resistance of these caps to be dominated by metal losses as the frequency is increased although the dielectric material will also contribute some loss. Normally the metal losses go up by sqrt(2) per octave and this is one way to try and model the efficiency vs frequency of the standard sensor. I plan to add this info at some point in this thread as the efficiency does degrade at just worse than sqrt(2) per octave.
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Regards
Jeremy --- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
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Re: HP 478A Thermistor Sensor. Input return loss and matching
Here's an image showing the completed matching adaptor that contains the series 11nH inductor.
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This is constructed using two precision N bulkhead connectors, one male and one female. I salvaged them from an old prototype RF filter but they are available from Mouser for about ?27 each. This is a very good price for an extremely good connector. These have 8 slots in the N connector and are designed to work well to many GHz.
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Whilst this connector choice may seem like overkill at 50 MHz, these high quality N connectors are similar quality to those used in a VNA in terms of the mating parts and this is what you would want for something mating to a power meter where you want repeatable connections.
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You can see that I've soldered them together with a soldered metal outer ring and there is a series inductor inside. This construction method looks ugly but it will deliver very low additional losses.
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The N connectors are stripline launcher types which give a clean interface to the inductor. I think the Suhner part number for the male version is 13 N-50-0-33/133 NE
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When I measure with this inline I get the same VSWR response as the model with about 1.003:1 on the VNA. This is exploring the measurement limits of my VNA.?
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When I put it inline with the 1mW 50 MHz output of my power meter, there is no discernible change in level (compared to not having it inline) when I use the 432A with a DVM on the recorder output. I get 0.996x mW in both cases where the fourth digit drifts the same with and without the matcher inline. It requires careful operation of the zero to achieve repeatable results here.
The difference between 0.995 mW and 0.996 mW is? 0.004dB and the difference appears to be much less than this.
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So it looks like this is working just as well as the model predicted it would. I think I managed to get a Qu of much better than 65 for the 11nH inductor but I think the Q diminishes a bit once inside the metal enclosure. But it still performed as expected so I think the Q was still good enough once inside the matching enclosure.
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Regards
Jeremy
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For C14 & C20 the can has several tabs that secure them to the board - these are common with the "-" of the capacitor and the can itself is often used to complete the circuit.? Make sure that all of the tabs connected to the case are also connected to the "-" terminal if required.? The voltage rating of any replacement should be the same or higher than the originals and the capacitance value itself should be 20-50% higher than the original - the actual capacitance of the originals tended to be close to or above the indicated value while modern capacitors tend to be below the rated value (as close to the lowest limit of the tolerance band as the manufacturer can get away with.) No need to worry about low ESR on these however and, while not required, 105 deg C parts are a good choice IMO as they really don't cost much more than 85 deg parts and they will probably outlast us both in that application.
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Hal
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Re: HP 478A Thermistor Sensor. Input return loss and matching
I'd expect the 0.1uF caps in the H72 sensor to be class 2 ceramic types as it's hard to imagine COG/NP0 being used here. This would presumably make the reactance at 10kHz susceptible to temperature changes and this might also worsen the drift vs temperature if you tried to use it with a 431 meter. So there's probably more than one reason the H72 can't be used with the 431 meter.
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I'm not sure how stable the ESR of the 0.1uF caps will be over temperature up at 50 MHz but presumably these caps were chosen carefully by HP. The ESR of these caps will contribute to the efficiency factor stamped on the sensor as the ESR in these caps will rob a tiny amount of the incident power to the thermistor. However, the ESR will probably be tiny at 50 MHz. The ESR will increase up towards 1 GHz and this will cause some loss in efficiency as the ESR of class 2 ceramic caps does tend to climb rapidly up in the GHz range.
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The standard sensor will use thermally stable caps here with low ESR and I would expect the loss resistance of these caps to be dominated by metal losses as the frequency is increased although the dielectric material will also contribute some loss. Normally the metal losses go up by sqrt(2) per octave and this is one way to try and model the efficiency vs frequency of the standard sensor. I plan to add this info at some point in this thread as the ESR does degrade at just worse than sqrt(2) per octave.
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Regards
Jeremy
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Trevor Gale
Jared Cabot
Sergey Kubushyn
Harold Foster