The Heath AM-2 is basically a "moni-match" type of SWR bridge. It was designed
for 160-meters through 10-meters and usable on 6-meters. Above 54 MHz the accuracy
of the SWR scale is very questionable. It will indicate the lowest SWR at higher
frequencies but the actual SWR value shown on the meter will not be accurate.
By changing the internal calibration resistors, it can be used on either a 50-ohm or 72-ohm system.