50/75 ohm load with 50 ohm thermal converter.

[dminesinger]

Need to calibrate my HP/3335A. Calls for a 75 ohm thermal converter. We don't own one. Can I use a 50/75 ohm load with 50 ohm thermal converter. Been to long to remember. Last time limited calibrated it to 75 ohm not calibrated. Have not needed it in a year. We will probable do that again this year.

[briansalomon]

I don't think you can use a matching/minimum loss pad because the flatness spec for the 3335A is +/- 0.07 to 25Mhz and 0.15 to 80Mhz.

Matching pads don't have the flatness spec you need. Here's one from minicircuits http://www.minicircuits.com/pdfs/BMP-5075R+.pdf

If you need the 75 ohm output, I think you need a 75 ohm thermalconverter.

[N79]

I agree I think you're out of luck. You can't increase the impedance without some tradeoff or modification to your test signal and you can't use the 50 ohm thermal converter's calibrated values due to mismatch.

As an aside, this problem comes up enough that something should be done about it. I'm working on a project now that will address it, but it's still in the R&D phase; it's basically a wideband unity-gain amplifier with ppm-level accuracy. In your case you would plug this in between your test unit and your thermal converter and all your problems would be solved!

[briansalomon]

If you have time, I would like to know how you're progressing with your project. I think it would be interesting and beneficial to the community to know how someone at your level goes about developing and certifying a new standard.