This is a well known phenomenon which manifests itself by the picking up of the same short wave station at two nearby points on the receiver dial.
- It is causal because of poor front end selectivity that is inadequate image frequency rejection.
- Intermediate frequency(IF) stage takes care of eliminating different adjacent signals.
- If there is no RF Amplifier in a receiver then it suffers badly from double spotting.
- Suppose if a receiver having an Intermediate frequency of 455 KHz. There is a strong station 14.7 MHz and a weak station 13.79 MHz. If a receiver is turned to 14.7 MHz (strong station) then receiver picks up same station. But if Receiver is tuned to a weak station 13.79 MHz then also receiver picks up near by strong station 14.7 MHz.
- Double spotting is harmful because a weak station may be marked by the reception of nearby strong station.
- An improvement in image frequency rejection will reduce Double spotting.
- One advantage of Double spotting is , it is used to calculate intermediate frequency of an unknown receiver.
