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The commonly agreed industry standard for the maximum acceptable input VSWR is 1.5:1, which is equivalent to 14 dB return loss.
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I've never heard of such a standard. Could you provide a reference? If you are making measurements, 1.5 seems really high.
Looking at the manual for my LeCroy 7200, they spec the VSWR at 1.2, BW is 4GHz with a 125pSec transition for 50mV and up. Isolation is 60dB min at 1GHz.
I have no reference to such a standard – my statement is based solely on the impression left by various RF literature, experience and common sense. Sorry if it has been misleading.
At least one example, showing that I’m not the only one who thinks 1.5:1 is the limit of acceptable (some might call it ideal) VSWR, can be found here:
https://www.ahsystems.com/notes/VSWR-return-loss-sheet.php A VSWR of less than 1.5:1 is ideal, a VSWR of 2:1 is considered to be marginally acceptable in low power applications where power loss is more critical …
Very few oscilloscopes have the input return loss / VSWR specified; one of the few exceptions was the now discontinued 2 GHz R&S RTE. From the data sheet Version 16.01:
Input VSWR : input frequency ≤ 500 MHz 1.25 (meas.); input frequency > 500 MHz 1.4 (meas.)
I take from this, that a company, that is renowned to be an RF-specialist since 1933, has no problems specifying a VSWR of 1.4:1 for frequencies >500 MHz on an instrument that isn’t exactly a cheap low-end product. There exists no VSWR-specification for its successor, the MXO5, anymore…
Finally, the common-sense part: A VSWR of 1.5:1 means 4 % reflected power, i.e. 4 % power loss at the receiver end (scope input). That’s 0.17 dB = ~2% voltage error. It is less than the DC-accuracy specification of most oscilloscopes.
As can be seen from my measurements, the 500 (actually 570) MHz SDS2000X HD provides a VSWR of <1.25:1 up to ~750 MHz. That should be in line with your expectations based on the LeCroy 7200.