library(DBI)
library(tidyr)

con <- dbConnect(RPostgres::Postgres(), dbname='mainscnt', host='172.16.10.27', user='wn')
res <-dbSendQuery(con, "select time, location, freq from mainsfrequency where valid=1 and time >= '2021-08-05T00:00:00.0Z' and time < '2021-08-06T00:00:00.0Z'")
devices <- dbFetch(res)
dbClearResult(res)
dbDisconnect(con)

d2 <- devices %>% pivot_wider(names_from = location, values_from = freq)