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| Inexpenive 50 Ohm Feed Through Terminations |
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| joeqsmith:
Experiments with a damaged part. https://www.eevblog.com/forum/testgear/pasternack-pe6008-50-thru-term/msg947602/#msg947602 |
| graybeard:
--- Quote from: joeqsmith on July 26, 2019, 11:01:19 am ---Experiments with a damaged part. https://www.eevblog.com/forum/testgear/pasternack-pe6008-50-thru-term/msg947602/#msg947602 --- End quote --- Joe, I believe you were measuring the termination itself. You did not measure it on the input of a scope. I suspect if you try that again with the termination on a scope or meter input there well be very little difference for the various configurations. Making a calibration termination (not a feed through) is far more critical. I have made SMA cals for my VNA using two 100 ohms 0805s based on this article. Chris |
| joeqsmith:
--- Quote from: graybeard on August 11, 2019, 03:47:46 am --- --- Quote from: joeqsmith on July 26, 2019, 11:01:19 am ---Experiments with a damaged part. https://www.eevblog.com/forum/testgear/pasternack-pe6008-50-thru-term/msg947602/#msg947602 --- End quote --- Joe, I believe you were measuring the termination itself. You did not measure it on the input of a scope. I suspect if you try that again with the termination on a scope or meter input there well be very little difference for the various configurations. Making a calibration termination (not a feed through) is far more critical. I have made SMA cals for my VNA using two 100 ohms 0805s based on this article. Chris --- End quote --- I agree that with a meter you wouldn't likely see any difference, outside of the resistance tolerance of the parts. All of the meters I have, run at DCish. I had ran some test using 0805s vs the 1206 and also saw some improvement. This is why the cal standard for my old 8754A is using two 100 ohm 0805's for the load. I should have saved that data. My scopes have 50ohm support. There is no way to disable it on my higher BW unit. I made a video a while back for someone who had asked me about measuring the speed of light. In that video, I show many tests, some optical. One test was looking at a square wave using my function generator and my slower scope. I did this to show the contrast to the sub ns edges we would be looking at for the other experiments. Granted, when you are not looking at transmission lines, the termination will be less important, just like with a meter. |
| ocw:
--- Quote ---I had ran some test using 0805s vs the 1206 and also saw some improvement. This is why the cal standard for my old 8754A is using two 100 ohm 0805's for the load... --- End quote --- I have had better luck using Vishay FC0603E50R0BST1 RF resistors. They 50 ohm 1/8 watt 0.1% 0603 resistors with a factory rating of under 1.2/1 VSWR up to 30 GHz for just $1.61 (Qty 1 Mouser). See: https://www.mouser.com/datasheet/2/427/fcseries-947854.pdf Those have worked better for me than using two 100 ohm 0.01% regular resistors. I prefer staying away from the similar FC0603E50R0BTBST1 resistors since they only have top sided soldering. |
| ocw:
--- Quote ---I am very interested in seeing your test data --- End quote --- With my prior 2 x 100 ohm on a SMA connector load being trashed, I thought that I would make a new one using two APC0603T100RZ 100 ohm 0.01% resistors. It came out better than my prior one--I was impressed! The attachment shows my Anritsu MT8222A evaluation of it. I decided to use that instead of my Agilent E7495A or HP 8753C. I used a Suhner 18 GHz calibration load rather than one of my four other choices. I compared those and thought that the Suhner produced the most accurate results. |
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