SSDR ver 3.3.29 SWR=1.4 on PGXL is always ON without any TX !

Looking deeper into the Flex Meters;

Using the Flex API, I commanded Flex to show me the meter list.

For my Flex 6600, the PG-XL meter #12 is listed as an "External Meter," and is the "amp RL" value, meaning it gets the value from an external source, the PG-XL.

Flex Smart SDR uses meter #12 to calculate PG-XL SWR. The meter lists the meter output is scaled from 0 dB to 20 dB and is listed as PG-XL Return Loss (RL).

Return Loss is defined as "return loss is a measure in relative terms of the signal's power reflected by a discontinuity in a transmission line."

The formula to convert from Return Loss to SWR is:

where RL(dB) is the return loss in dB, Pi is the incident power and Pr is the reflected power.

where RL(dB) is the return loss in dB, Pi is the incident power and Pr is the reflected power.

Or for SWR:

For reference, 60dB RL is 1.0 SWR, 20dB RL is 1.22 SWR and 1 dB RL is 17 SWR.

Again, using the Flex API, I took a look at meter #12 output, with no TX. Meter #12 out was "20dB" (maximum scale value). Using the RL formula, this is an SWR of 1.22, which we see on our Smart SDR PG-XL panel.

Also, using the PG-XL API, I looked directly at what the PG-XL was reported as Return Loss, with no TX. The value was 60dB or an SWR of 1.0. However, my PG-XL utility shows an SWR of zero.

The PG-XL utility is causing the SWR indication to be zero, with no TX, but the Smart SDR indication for PG-XL is not using a TX flag (0) to show SWR as zero.

Interesting, with an RL scaled for a maximum of 20db, the Smart SDR will never show an SWR less than 1.22

In the case of the PG-XL, which outputs an RL of 60db, the best SWR indicated on its control panel will be 1.0.

Should be an easy fix for Flex to display zero SWR, when no TX, and rescale the RL range to 60dB, for a best SWR indication of 1.0.

Alan. WA9WUD