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I've been following this discussion about diode power sensors.
I assume the diode sensors fail because of blown diodes form overload. Has any repaired the faulty sensors by replacing diodes?
Mike N2MS ?
On November 17, 2018 at 6:33 PM "Ed Breya via Groups.Io" <edbreya@...> wrote:
Hi Tobias, I looked at the OP again, and realized that you already knew about the "mount" resistor - I didn't notice that the first time. I grabbed that 8484A manual pdf that Orin linked - thanks Orin, I have lots of 8484As, and the manual somewhere, but can never seem to find it. Now I have a fresh copy.
Anyway, after refreshing my memory on these sensors, and looking also at the 8481A schematic, I'd recommend studying both types - the TC and diode models have a different arrangement for the auto-zeroing function. The circuit you posted puts the AZ feedback to the detector, as in the 8481A TC circuit, but that won't work right. With the TC type, it is a low impedance source, so the AZ current can go through, and offset the signal. With a diode detector, you should use a circuit like in the 8484A, which applies it to the ground-side JFET switch in the chopper. The diode detector is a high impedance source, so you don't want to put the AZ feedback current there.
Good luck,
Ed
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Mike
almost all of the 848x series power sensor heads use a thermocouple and not a diode. The replacement thermocouples were at one time available? directly from HP/Agilent. They were crazy expensive (like $750) as I remember) plus you needed an eye loop and the nerves of a? Swiss watchmaker to replace them. What is essentially being attempted here is to make a diode version of the power sensor head as a replacement since the heads have become scarce and expensive in their own right.
Why you might ask did the then HP choose a thermocouple? I suspect that the thermocouple is more linear than a diode sensor and generally flatter over a wide frequency range. If your willing to trade off dynamic range and wider bandwidth of the thermocouple then? the diode may be a a useful solution to lack of power heads available these days .. .I am hopeful that Tobias is successful.
Hope that helps
Dave
NR1DX
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On 11/18/2018 2:35 PM, n2msqrp wrote:
I've been following this discussion about diode power sensors.
I assume the diode sensors fail because of blown diodes form overload. Has any repaired the faulty sensors by replacing diodes?
Mike N2MS
On November 17, 2018 at 6:33 PM "Ed Breya via Groups.Io" <edbreya@...> wrote:
Hi Tobias, I looked at the OP again, and realized that you already knew about the "mount" resistor - I didn't notice that the first time. I grabbed that 8484A manual pdf that Orin linked - thanks Orin, I have lots of 8484As, and the manual somewhere, but can never seem to find it. Now I have a fresh copy.
Anyway, after refreshing my memory on these sensors, and looking also at the 8481A schematic, I'd recommend studying both types - the TC and diode models have a different arrangement for the auto-zeroing function. The circuit you posted puts the AZ feedback to the detector, as in the 8481A TC circuit, but that won't work right. With the TC type, it is a low impedance source, so the AZ current can go through, and offset the signal. With a diode detector, you should use a circuit like in the 8484A, which applies it to the ground-side JFET switch in the chopper. The diode detector is a high impedance source, so you don't want to put the AZ feedback current there.
Good luck,
Ed
--
Dave
Manuals@...
www.ArtekManuals.com
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I’ve long thought about using one of the Linear Tech or Analog Device RF sensor ICs as a front end to an HP power sensor head with blown thermistor/diode.
They have a great frequency and sensitivity range, come in a tiny package that could fit in an existing head, and come in linear and log versions.
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On Nov 18, 2018, at 15:48, Artekmedia <manuals@...> wrote:
Mike
almost all of the 848x series power sensor heads use a thermocouple and not a diode. The replacement thermocouples were at one time available directly from HP/Agilent. They were crazy expensive (like $750) as I remember) plus you needed an eye loop and the nerves of a Swiss watchmaker to replace them. What is essentially being attempted here is to make a diode version of the power sensor head as a replacement since the heads have become scarce and expensive in their own right.
Why you might ask did the then HP choose a thermocouple? I suspect that the thermocouple is more linear than a diode sensor and generally flatter over a wide frequency range. If your willing to trade off dynamic range and wider bandwidth of the thermocouple then the diode may be a a useful solution to lack of power heads available these days .. .I am hopeful that Tobias is successful.
Hope that helps
Dave
NR1DX
On 11/18/2018 2:35 PM, n2msqrp wrote:
I've been following this discussion about diode power sensors.
I assume the diode sensors fail because of blown diodes form overload. Has any repaired the faulty sensors by replacing diodes?
Mike N2MS
On November 17, 2018 at 6:33 PM "Ed Breya via Groups.Io" <edbreya@...> wrote:
Hi Tobias, I looked at the OP again, and realized that you already knew about the "mount" resistor - I didn't notice that the first time. I grabbed that 8484A manual pdf that Orin linked - thanks Orin, I have lots of 8484As, and the manual somewhere, but can never seem to find it. Now I have a fresh copy.
Anyway, after refreshing my memory on these sensors, and looking also at the 8481A schematic, I'd recommend studying both types - the TC and diode models have a different arrangement for the auto-zeroing function. The circuit you posted puts the AZ feedback to the detector, as in the 8481A TC circuit, but that won't work right. With the TC type, it is a low impedance source, so the AZ current can go through, and offset the signal. With a diode detector, you should use a circuit like in the 8484A, which applies it to the ground-side JFET switch in the chopper. The diode detector is a high impedance source, so you don't want to put the AZ feedback current there.
Good luck,
Ed --
Dave
Manuals@...
www.ArtekManuals.com
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On 11/18/18 4:30 PM, wrote: I’ve long thought about using one of the Linear Tech or Analog Device RF sensor ICs as a front end to an HP power sensor head with blown thermistor/diode.
They have a great frequency and sensitivity range, come in a tiny package that could fit in an existing head, and come in linear and log versions. A local friend and I have done a lot of work on exactly that. The idea has great potential, but there are some dragons hiding. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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On Sun, Nov 18, 2018 at 12:48 PM Artekmedia < manuals@...> wrote: Mike
almost all of the 848x series power sensor heads use a thermocouple and
not a diode. The replacement thermocouples were at one time available?
directly from HP/Agilent. They were crazy expensive (like $750) as I
remember) plus you needed an eye loop and the nerves of a? Swiss
watchmaker to replace them. What is essentially being attempted here is
to make a diode version of the power sensor head as a replacement since
the heads have become scarce and expensive in their own right.
"parkertest" on ebay seem to have bought a lot of replacement thermocouples and are selling them at $7200 obo for 20!
They will also repair an 8481A for $465 or sell a refurbished one for $475 obo.? Kind of puts a limit on the value of these things.
?
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A long time ago, I remember an eBay seller offering NOS HP replacement thermocouples, with calibration labels, at incredibly low starting bid prices.? I really don't think he knew what he was selling.? I can only imagine the seller's surprise at the ensuing bidding frenzy.? Those silly little pieces of bent wire were worth a lot of money!??
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Thermocouple detectors are definitely more linear, RMS, and have been around very long time. Some of the peak power meters use the diode versions. These typically have lower dynamic range. The HP8900D uses diode detectors for peak reading. Analog Devices bought Linear Technology but they are still selling independent product lines so the power detector IC's are there. We designed a detector based on one of their log-amp based power detectors that reads linear voltage for dB RF. It was a mistake and so I found the ADL5511 which has both voltage for dB in and also envelope. It also has temperature compensation to first order. Envelope is perfect for peak reading. We have built over 60 of these in a small pod, that has a PIC to take care of curve fit and they track our Keysight and Boonton meters on single frequency (which is what we needed). There are numerous companies now making USB power heads that go direct into a PC, like R&S, LadyBug (ex HP), Keysight, MiniCircuits. They all use the new generation ICs.
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Hi all,
I made some further progress. I discarded my previous prototype and made a new one using better JFETs, this time the 2N4856A. According to its datasheet it is especially designed for chopper applications (well, I don't quite understand in which parameters a chopper JFET should differ from an ordinary JFET).
And with the new JFETs, indeed, the waveforms at the chopper output look much cleaner and nicer. However it is difficult to measure because my scope (Agilent 54832B) is very noisy with those small voltages.
I was able to get more stable and reliable readings, and the zeroing of the sensor also works more reliable. However, the linearity is still quite bad; at low input power, it is okay but towards increasing output power, linearity degrades quickly and at the worst point (0 dBm input into the detector) it is almost 3dB off. My detector can measure -30dBm to 0dBm with usable accuracy. Above it becomes a bit nonlinear - could be due to the diode no longer operating in the square law region. But I will further investigate in the subject. Probably I also need to add the shaping network mentioned in the 8484D service manual.
@ Dave NR1DX
I am testing the diode detector with the HP 436A calibration output. And I also test at various frequencies down to 1MHz and up to 2.6GHz with the 8663A signal generator. However, I think later it would be desirable that my detector works to, say, 6 to 10 GHz. I think otherwise it is not very useful. On the other hand it would also be good if it works to below 1MHz.
@ Rainer DF6NA
Thanks for the links. I will probably order some of those connectors when I am ready for a 'real' prototype! looks not toooo expensive.
@ Mike N2MS
I think for the diode sensors (like 8484A, 8481D) it is not possible to replace the diode without a highly sophisticated workshop and tools. I have never seen one of these sensors from the inside, but I expect wire bonded black magic inside; the service manual even says that the position and shape of certain wires is important, otherwise the calibration goes nuts.
@ Dave NR1DX
The thermocouple has the advantage that it really measures power dissipation, i.e. RMS. Since it does the measurement via temperature, it is basically independent of the waveform and even independent of the frequency - as long as the mechanics is reliable and precise enough, you can measure each frequency with this, even DC. The HP sensors have an internal DC blocking capacitor, so this is why they don't work down to DC.
@ bownes
yes, like AD8307 or so would be nice as well. However, I am not sure whether it is possible to connect these somehow to a HP meter like the 436A. For instance, the AD8307 (or some other LogAmps) need a power supply, which is not available on the existing interface to the sensors, except if you abuse some signals, e.g. the chopper signals and then rectify them etc.
Besides that, you need to mimic the behaviour of the thermocouple/diode detector signals.
This is why I stuck to the 8484A/8481A design.
@Dave McGuire, AK4HZ
You said you have already done what bownes suggested? was it working? could you tell a bit more about this? :-)
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has info and diagram of sensor internals.
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On 11/19/18 4:42 PM, Andy ZL3AG via Groups.Io wrote: has info and diagram of sensor internals. The article "Very-Low-Level Microwave Power Measurements" shows why a diode sensor is good for low levels, not 0dBm, so it's good for measuring low power chip radio output with a receiving antenna a few meters away from the transmit antenna in preparation for FCC certification testing. I want one.
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some good reading here.
https://www.boonton.com/forms/principles-of-power-measurement-form
Easier to search for "boonton principles of power measurement"
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwisu_-Fm-LeAhWKmuAKHbrfAuAQFjABegQIAxAC&url=http%3A%2F%2Fwww.boonton.com%2F~%2Fmedia%2FBoonton%2FReference%2520Guides%2FWTG_RefGuide_F1128_sm_web.ashx&usg=AOvVaw3CUwYZFunzbmZd4JDw4qhH
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On 11/20/2018 12:15 AM, RFI-EMI-GUY
wrote:
some good reading here.
Easier to search for "boonton principles of power measurement"
Boonton has always made some very nice equipment, I own a Boonton
peak power meter that also reads CW power, down to about -70dBm and
up to +10dBm, with provision for external 30dB pad via switch.
No CRT or solid state display, it has a numerical display. Don't
know how old it is, but the last time I used it (quite a while ago)
it worked perfectly.? That URL (the big long one) has a LOT of good
info.
--Doug, WA2SAY, retired RF engineer
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Beginning at around 47:50, in the following video,
he discusses HP tc and diode power sensors, and shows a strip down of a diode one.
There is some focused discussion about the theory of operation (for tc and diode types)… and you can see the tools he uses to examine the blown diode sensor, for possible repair.
Roy VE3RFT
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Hi Tobias, Do you have any more information on the substitute 8481A you are developing?
Di you make something that worked?
Would really appreciate any reply to explaining where you got to and if it is possible to make a substitute part?
Yours sincerely Jeff ZL4AI
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Any significant differences between the HP 5347/8's for use with the power sensors?? ?I'll read through the attached links and data again later this winter once the snow falls.? Saved for now.?
From my newbie limited background; seems the old Pacific Measurements (PMI) were single thermocouple/diode and the later Wavetek were dual along with the subsequent Gigatronics and I think the HP's if I recall offhand.? ?
From what IMSAI Guy noted with the Wavetek/Gigatronic..., you can't find the diodes, then you'd have to calibrate and know how to program the EPROM.?
Then again, where there is a will there is a way.?
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After a couple of seconds of stupidity eighteen months ago, I could certainly be interested in looking at, and perhaps contributing to, the design of an internal PCB for an 8484 which lies dismantled, waiting for either a working replacement capsule or a reproducible, compatible, (diode-based) detector design.
Compliments of the season to all!
Chris Bartram
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Hello, I follow your topic on the homemade diode power sensor for HP meters, please can I get the diagram to make one? I buy one HP436A but no sensor.
Thank you in advance, Francesco.
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This topic is on the dead track?? It is one very interesting topic, considering there is one Hi number of HP 435, 436, 437 models for a low price is a good opportunity for small lab and student on the RF world to grab one of these simple instrument for 50/100 pounds, the big problem the second-hand market is on the hand of surplus scavengers they sell the hold and rusty powerhead at Hi price.
Way no make one at a low price and nice fun to handmade one with some good result making a one-hybrid system like es: detector AD8318/17 the chopper, and the amplifier using the 8484A diagram using the chopper FET circuit and the NPN Transistor amplifier.
If you need one power meter to make money BUY one 12.000 meters, but for hobby student and small lab the approach of Tobias whos the good one.
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On 5/30/21 1:14 PM, Francesco wrote: This topic is on the dead track?? It is one very interesting topic,
considering there is one Hi number of HP 435, 436, 437 models for a low
price is a good opportunity for small lab and student on the RF world to
grab one of these simple instrument for 50/100 pounds, the big problem
the second-hand market is on the hand of surplus scavengers they sell
the hold and rusty powerhead at Hi price.
Way no make one at a low price and nice fun to handmade one with some
good result making a one-hybrid system like es: detector AD8318/17 the
chopper, and the amplifier using the 8484A diagram using the chopper FET
circuit and the NPN Transistor amplifier. Some people have done this. I had something very much like this running in a bench test configuration several years ago. It worked reasonably well, but not well enough to productize, and there were still unresolved problems. The power sensor interface is simple, but not quite as simple as it looks. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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Thank you Dave for the imput to this post, I'm aware there is some difficulty fot the detectot part on the power head.
I hope if there someone want share is exsperience and like give some sugestion and diagram to help to build one will be apreciate.
Francesco.
G7OYO
?
?
Sent:?Sunday, May 30, 2021 at 6:47 PM
From:?"Dave McGuire" <mcguire@...>
To:[email protected]
Subject:?Re: [HP-Agilent-Keysight-equipment] A homemade diode power sensor for HP meters
On 5/30/21 1:14 PM, Francesco wrote:
> This topic is on the dead track?? It is one very interesting topic,
> considering there is one Hi number of HP 435, 436, 437 models for a low
> price is a good opportunity for small lab and student on the RF world to
> grab one of these simple instrument for 50/100 pounds, the big problem
> the second-hand market is on the hand of surplus scavengers they sell
> the hold and rusty powerhead at Hi price.
> Way no make one at a low price and nice fun to handmade one with some
> good result making a one-hybrid system like es: detector AD8318/17 the
> chopper, and the amplifier using the 8484A diagram using the chopper FET
> circuit and the NPN Transistor amplifier.
Some people have done this. I had something very much like this
running in a bench test configuration several years ago. It worked
reasonably well, but not well enough to productize, and there were still
unresolved problems. The power sensor interface is simple, but not
quite as simple as it looks.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
?
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bownes
Dave McGuire
RFI-EMI-GUY
jafinch78 .
Francesco