Unpivot paired columns

Hello DDON 

you can add a new column with this formula, delete all your S and F-fields and then expand the list to rows and then expand the record

let 
            CreateNumber = List.Numbers(0,3),
            TransformToValuesFS = List.Transform 
            (
                CreateNumber,
                (item)=>   [F=  try Record.Field(_, "F[" & Text.From(item) & "]") otherwise null , S= try Record.Field(_, "S[" & Text.From(item) & "]") otherwise null] 
            ),
            CleanNulls = List.Select(TransformToValuesFS, each _[F] <> null and _[S]<>null)
        in 
            CleanNulls

This is quite complex you have to pay attention on the following

Adapt this number to your maximum numbers of pairs   --> CreateNumber = List.Numbers(0,3)

Adapt this text according your standard naming of your F and S-columns

(item)=> [F= try Record.Field(_, "F[" & Text.From(item) & "]") otherwise null , S= try Record.Field(_, "S[" & Text.From(item) & "]") otherwise null]
)

Here the complete code

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjLWMzDSMzJU0lFKTEoGkiCWERAbA7GJUmwsAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [DateTime = _t, IMEI = _t, #"F[0]" = _t, #"F[1]" = _t, #"S[0]" = _t, #"S[1]" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"DateTime", type date}, {"IMEI", type text}, {"F[0]", Int64.Type}, {"F[1]", Int64.Type}, {"S[1]", Int64.Type}, {"S[0]", Int64.Type}}, "de-DE"),
    AddPairs = Table.AddColumn(#"Changed Type", "Pairs", each let 
            CreateNumber = List.Numbers(0,3),
            TransformToValuesFS = List.Transform 
            (
                CreateNumber,
                (item)=>   [F=  try Record.Field(_, "F[" & Text.From(item) & "]") otherwise null , S= try Record.Field(_, "S[" & Text.From(item) & "]") otherwise null] 
            ),
            CleanNulls = List.Select(TransformToValuesFS, each _[F] <> null and _[S]<>null)
        in 
            CleanNulls),
    #"Removed Other Columns" = Table.SelectColumns(AddPairs,{"DateTime", "IMEI", "Pairs"}),
    #"Expanded Pairs" = Table.ExpandListColumn(#"Removed Other Columns", "Pairs"),
    #"Expanded Pairs1" = Table.ExpandRecordColumn(#"Expanded Pairs", "Pairs", {"F", "S"}, {"F", "S"})
in
    #"Expanded Pairs1"

this transforms this

into this

Copy paste this code to the advanced editor in a new blank query to see how the solution works.

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Kudoes are nice too

Have fun

Jimmy