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Locked Lothar Baier - please explain the possible 8703A -> 8720B deception

 

Lothar,
On 9th August 2023 you offered for sale a 130 MHz to 20 GHz 8703A? lightwave analyzer.


You stated that had bought 2 and "I removed the optical testsets to use them for parts"

You went on to say

"this is a great unit for someone who wants a compact VNA but can not afford a 8720B or for someone who has a broken 8720B and wants to get it back running"

Clearly from this you considered an 8720B to be more valuable than an 8703A with the optical test set removed.?

Then on 29th March 2024 you offered for sale what you said you believed with an 8720B. Anyone that receives the list via email will have the link, but the link is no longer valid as you deleted the posts - see screenshot of what I can see as an admin.


You wrote it was offered for sale on behalf of a widow of a friend, an

"HP VNA? 130MHz-20GHz , appears to be 8720B no sticker on unit.? , good condition $1650"

As you know, a potential buyer from Iceland backed out of the deal when he became suspicious that the item with no label was actually the 8703A you had advertised 6 months earlier. The differences and similarities between the? photographs are as follows.

1) A label to the right of test port 2, with part of the label scrubbed out is seen in all photographs

2) A label under the test port 2 is seen in all photographs

3) The part number which was clearly visible on the photograph posted last year has been removed.

I have attached 3 photographs - two clearly showing the model number is an 8703A, and another with the model number and function removed, and it just showing "130 MHz - 20 GHz analyzer" rather than the "8703A 130 MHz - 20 GHz Lightwave Component Analyzer" in the photographs posted previously.

F1EKU has since provided his view that the instrument you were selling was indeed an 8703A. I have not checked out F1EKU's comments, but I am even without looking, I am sufficiently concerned about this to ask for your comments.?

Can you please shed any light on this matter? Do you accept that they are the same instrument? Why, if you had done nothing wrong, did you feel the need to delete the messages?

Dave (group owner).

--
Dr David Kirkby Ph.D
Kirkby Microwave Ltd
Email: drkirkby@...
Web:
Telephone 07910 441670 (UK) or +44 7910 441670 (international)
Registered in England and Wales, company number 08914892.?
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT


no-name.jpg
8703A-1-cable-attached.jpeg
Lotha-Baier-deleted-his-own-posts.png
8703A-2-cables-attached.jpeg
Lotha-Baier-deleted-his-own-posts.png

Re: Testing Scope Probes

 

What do you think is going to be special about the 10073C that means the Rp will stay at 2.2Meg even up at VHF and UHF??

I just measured one for you. Rp falls in a similar way to other x10 scope probes. This should be no surprise because there's going to be a compensation cap in the tip (across a large tip resistance) and this is going to be in series with a deliberately lossy transmission line. The reason the Rp falls is partly because of the lossy coax cable in series with the tip capacitor.

Plot Rp vs frequency for a lossy capacitor and you will see Rp falling with frequency.

This stuff isn't difficult or technically challenging.

Some of you shouldn't be offering advice to Jinxie because you seem so inexperienced.
Re: Testing Scope Probes

 

Posts crossed agin, I'm doing other things.

The Tek example is a 10M 100MHz probe. That is not the same as the 10073C.
Re: Testing Scope Probes

 

On 2024-04-11 09:06 AM, jmr via groups.io wrote:
The parallel capacitance won't be a constant 12pF, it will fall slightly up at VHF and UHF.
I've been following this discussion with interest, no particular expertise to contribute. Is your statement above based on the leads and other parasitics adding some inductance, which starts to cancel the capacitance at higher frequencies?

Steve Hendrix
Re: Testing Scope Probes

 

I've just measured a 10073C probe on an analyser for Rp Cp and XP vs frequency up to 500MHz. See the plot below.

There should be no surprises in the result below as many x10 scope probes will look like this.
Re: Testing Scope Probes

 

No,
I've not measured a high impedance 'scope probe on a VNA (which is typically intended for 50R systems). I'm away from home on business so won't be doing so any time soon (I have a number of VNAs).

When HP / Agilent / Keysight say the probe input impedance is 2M2 in parallel with ~12pF I tend to belive them. I cannot see where you are getting a RESISTANCE of 60 Ohms from.

As it is close to the reactance of the "missing" 6pF on your simulation maybe it make little difference, but surely, lacking any other data your simulation should use the published 2M2 in parallel with 12pF values for the 10073C?

Robert.
Re: Testing Scope Probes

 

If it helps, look at the Tek datasheet in the link below. It shows Rp vs frequency for a typical 100MHz x10 scope probe.

The input Rp for the 10073C will be fairly similar vs frequency. It will fall below 100 ohms by a few hundred MHz.



The parallel capacitance won't be a constant 12pF, it will fall slightly up at VHF and UHF.?
Re: Testing Scope Probes

 

Jeez, I've just read all the recent replies. Have none of you ever measured a x10 scope probe before?
You can't assume the Cp will remain at 12pF up at UHF.
Also, the Rp will fall with increasing frequency. Only a novice would expect the Rp to still be 2.2M up at VHF and UHF.

It's going to look like about 60R Rp resistance in parallel with 7pF up at 400-500MHz.

Down at (say) 10MHz it might look like 12pF in parallel with about 20k ohm Rp.
Re: Testing Scope Probes

 

No I'm not counting the capacitance twice.?

Rp is a measure of parallel resistance not parallel capacitance. At 400-500MHz, the 10073C will load a circuit in a similar way to the loading caused by a perfect 60R resistor in parallel with about a 7pF perfect capacitor. i.e. just as I drew it on the circuit.

Have you ever measured a x10 scope probe using an analyser??
Re: Testing Scope Probes

 

On Thu, Apr 11, 2024 at 02:45 PM, Robert G8RPI wrote:
Crossed with Raymonds reply.
You saved my day...

Raymond
Re: Testing Scope Probes

 

On Thu, Apr 11, 2024 at 02:37 PM, Robert G8RPI wrote:
But you have Rp and 7pF probe capacitance.
That is counting the input capacitance twice.
Hi Robert,
Is that meant as an answer to my question? I'd say (HP spec) Rp = 2.2MOhm, Cp = 12pF, resulting in |Xc| less than 30Ohm @ 500MHz, or no? I'm confused...

Raymond
Re: Testing Scope Probes

 

Crossed with Raymonds reply.
I was assuming the probe input capacitance was 12pF. Seems odd to split the reactive impedance.

Robert.
Re: HP8568B battery replacement

 

On Thu, Apr 11, 2024 at 10:57 AM, Gianni Becattini wrote:
My had both, but I concluded that the big one (HP-67 style) was not used, so I changed only that on board and it works.

Hi Gianni,

I'm one of the many that have admired your beautiful books from the beginning but haven't posted about that.

As regards your above post, I'm not sure what you mean by "both": Two NiCds? BTW, the HP-67 also uses the smaller 3-cell (HP-35 style) battery, the HP-97 (and HP-91) use the bigger, 4-cell type.

Raymond
Re: Testing Scope Probes

 

But you have Rp and 7pF probe capacitance.
That is counting the input capacitance twice.
Re: Testing Scope Probes

 

> By contrast, a 10073C will typically look like about 60R in parallel with about 7pF across 400MHz to 500MHz.
>
Not relevant for the discussion but what's the math behind that? HP 10073C data 2.2MOhm // 12pF.

Raymond
Agilent E4406A Pulling down the power supply not starting

 

I have one E4406A with the same problem. I didn't disassemble it. I saw comments that could be the power source. Do I check the power source directly?
It has the same characteristic sound. And it does the same as the video in these links. Strange that before it was working perfectly.
Re: Fume extractor recommendation

 

¿ªÔÆÌåÓý

It would have been interesting to measure the lead levels in consumer electronics techs 50 years ago (and still today) who lit cigarettes with soldering irons. Adding lead to that menagere of poisons had to have been a death wish. I have seen sheet metal workers and plumbers do it. Cartoons in old QST magazines showed a group of hams building a transmitter and doing it as well.

? Bruce Gentry, KA2IVY






On 4/11/24 0:42, Chuck Harris wrote:

Hi Radu,

You don't say what your scare was, but if your doctor
deduced that the lead levels in your body are high, it
likely didn't come soldering circuit boards.

If you have lead in your blood, look first at hygene.

Lead won't penetrate your skin to any significant degree
from handling it, but it will from eating with unwashed
hands that have been handling lead.

Don't eat, drink, or put anything in your mouth while at
your bench.  Don't rub your eyes!  Always scrub your hands
after leaving your bench.

I have watched a lot of technicians chewing on wire
connectors, and wire insulation and using their mouths as 
a 3rd hand.  Don't!

Lead water pipes, and fresh lead soldered joints in water
pipes are an excellent way of building up the lead in your
body.

Workers that need to watch out for lead fumes typically work
around large circuit board wave soldering machines, or in a
factory making or recycling lead batteries.

Fume hoods used in soldering typically are just to reduce
irritation from flux smoke.

-Chuck Harris


On Wed, 10 Apr 2024 17:30:08 -0700 "Radu Bogdan Dicher"
<vondicher@...> wrote:

Hi all,
I've had a recent scare with potentially evil metals that can
vaporize - you know who you are.... - and absolutely need a good, and
hopefully affordable, solution for my bench soldering needs. And
hopefully, not just something I'll put on there for peace of mind but
have no idea if it really does anything. I really want this to work.

Are there any such things this community can recommend? I don't think
I can go used on this kind of thing, not knowing what Martian "deadly
on sight" materials the thing may have exhausted in its life. Nor I
really feel I can trust the vanilla low balling specimens on AMZ.
Being a health-related thing, I feel it kind of needs a trustworthy
solution, but my budget for this is limited.

Thank you for your input!
Radu.

Re: Testing Scope Probes

 

The R2 value of 60R is the equivalent Rp (parallel resistance) of the 10073C at about 500MHz. If you measured the 10073C with an impedance analyser down at low frequencies (eg in the kHz region) Rp would be about 2.2Meg ohm as you stated.
However, up at RF frequencies this value will fall at a fairly steady rate. A typical x10 probe might see Rp decline by a nominal factor of three every octave for example.

By 500MHz the Rp of the 10073C could easily be about 60 ohms.

The delta at 350MHz is about 1.5dB for the HB simulation. This is still poor enough to spoil the integrity of the Tee method in my opinion.
Re: Testing Scope Probes

 

Hi,
Where is R2 derived from? The 10073C input resistance is 2M2 not 60R. You have included the capacitance so can't be that unless you are double accounting?

What is the delta at 350MHz?

Robert.
Re: Testing Scope Probes

 

Of course, what this means in reality, is that you can expect to achieve slightly confusing results if you used this Tee setup to test the 10073C against a near perfect Zo probe for frequency response up to 500MHz.

If we assume that the Zo probe is perfectly flat to several GHz and it has an input Z of about 500R at 500MHz then the simulation tells us that there will not be a level playing field when comparing the two probes. The BNC tee will give the 10073C a 2-3dB voltage 'boost' at 500MHz in steady state. It may be the case that the 10073C will appear to match or even outperform the Zo probe at 500MHz in terms of frequency response if you chose this test method. Obviously, this is a false result.
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