# Surecom SW-102 VSWR meter review – v2.6

At Surecom SW-102 VSWR meter review I wrote a review of a meter which I had purchased a little over a year ago, it was at v4.5.

One of the many problems identified was inconsistency of displayed values.

## v2.6

Surecom’s versions are confusing, the highest number is not necessarily the latest version. It appears a partial version history from their current page advertising the SW-102 is:

```OLD VERSION : V3.3 ,V3.8 ,V4.5,V4.9 ,V5.0,V5.1 2017-8 NEW VERSION : V2.02 ,V2.03```

The following image is from Surecom’s current page advertising the SW-102, and I assume that the version shown here (v2.6) is the latest at time of writing.

The image captures the outputs of two tests with poor and good dummy loads. Let’s check the displayed values for internal consistency.

### Test 1

My interpretation of the display is that Pfwd=7.590W, Pref=0.818W, and VSWR=1.24.

Let’s calculate VSWR from Pref and Pfwd.

`VSWR=(1+(Pref/Pfwd)^0.5)/(1+(Pref/Pfwd)^0.5)`

Using Python (which uses ** instead of ^ for the exponentiation operator):

```>>> Pfwd=7.59 >>> Pref=0.818 >>> VSWR=(1+(Pref/Pfwd)**0.5)/(1-(Pref/Pfwd)**0.5) >>> VSWR 1.977469065572646```

This does not reconcile with the displayed VSWR value of 1.24

### Test 2

My interpretation of the display is that Pfwd=6.75W, Pref=0.072W, and VSWR=1.02.

Let’s calculate VSWR from Pref and Pfwd.

`VSWR=(1+(Pref/Pfwd)^0.5)/(1+(Pref/Pfwd)^0.5)`

Again using Python (which uses ** instead of ^ for the exponentiation operator):

```>>> Pfwd=6.750 >>> Pref=0.072 >>> VSWR=(1+(Pref/Pfwd)**0.5)/(1-(Pref/Pfwd)**0.5) >>> VSWR 1.2303495065340924```

This does not reconcile with the displayed VSWR value of 1.02

## A possible explanation

In fact, the displayed VSWR is given by `VSWR=(1+(Pref/Pfwd))/(1+(Pref/Pfwd))`which suggests that they either don’t know the correct formula, or did not implement it properly.

Such an error would have been obvious if the instrument was tested inline with an independent quality reference instrument.

## Conclusions

Though the notation for forward and reflected power is unconventional, the interpretation above seems reasonable.

The displayed values are internally inconsistent (ie, VSWR derived from FW and RW does not reconcile with displayed VSWR).

That suggests one or more of the figures are wrong which questions the usefulness of the instrument.

In a year, the quality does not seem to have gotten significantly better. The same problem was identified in the last report, though the output format was different.