Hi Bob,
You are correct about the type of resistors to use for measurements.? I mostly use BNC cables and devices, so I have built cal standards and measurement standards using BNC connectors as shown in the attachment.? I have tried to make my measurements as close to the reference plane as possible.? The resistors I use are 0805 film resistors and the capacitors are 0805 ceramic for the most part.? Since most of my work is done at HF, the calibration tolerances are not as tight as for VHF and UHF.
Tom?? W0IVJ
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On 10/27/2022 6:00 AM, Bob Ecclestone VK2ZRE wrote:
Hello Tom,
I noticed the format change just after I sent the post:-(
However the frequency difference was what caught my eye and I got "blind sided".
I agree with your comment, however, given other posts on component testing, defining a "pure resistance" is an interesting concept:-)
There was no mention of the test fixture or of resistor type, carbon, metal film or wire wound. A 10 ohm carbon film or wirewound resistor would have a very different response at 30Mhz compared to 1Mhz.
I repaired a piece of kit used to high voltage test sub station power transformers many years ago and it had a Philips 100 ohm 1 watt carbon resistor in series with the vertical input to the integrated CRO in the instrument.
The resistor was fried by a flash over and I was a bit puzzled at first because it was such a low series resistance in what was a high impedance input. I then twigged that it was, in fact, being used as a peaking coil.
Those Philips resistors had the carbon film deposited on the tubular ceramic substrate and then laser etched in a spiral to the required value. Lovely stable inductance!
However, the Smith Chart marker in the post is still on the real axis in both screenshots, negligible +j component. Like said, blind sided:-(
73...Bob VK2ZRE
On 27/10/2022 1:04 am, Tom Thompson W0IVJ wrote:
Hi Bob,
The issue was the values appearing on? S11(Smith chart) which DiSlord cleared up nicely.? By? the way, if you have the S11 port terminated in a pure resistance with no transmission line, the frequency makes no difference.? Even though the resistance is other than 50 ohms, the reading will be the same independent of frequency.
Tom?? W0IVJ
On 10/26/2022 7:00 AM, Bob Ecclestone VK2ZRE wrote:
Hi All,
I may have missed something here, but these screenshots are not comparing apples to apples.
In the first screenshot the marker is at 1MHz and in the second it is at 30MHz.
Given all the posts in this group about component testing and test fixtures, may I humbly suggest the "error" has more to do with marker frequency than software version.
73...Bob VK2ZRE
On 25/10/2022 8:06 pm, Tom Thompson wrote:
Here are the results of the two different firmware with a 10 ohm resistor attached to the S11 port.
Tom?? W0IVJ
On 10/24/2022 9:42 PM, DiSlord wrote:
Smitch chart marker value must be correct in all versions.
I think you select different smith marker format (Re+Im for example)
Provide screenshot
