# Aliased Signal's Frequency

So I have an incoming signal of 137.9 MHz and a sampling frequency of 1.4 MHz. Once sampled how do I calculate the aliased signal's new frequency? Bandwidth is 38 kHz with a subcarrier of 2400 Hz, if that information is relevant. Just looking for an equation to calculate the aliased frequency.

The hardware used is a RTL-SDR into a computer sampling at 1.4 MSPS.

This is the signal's information page:

https://www.sigidwiki.com/wiki/Automatic_Picture_Transmission_(APT)

• If you're using RTL-SDR or some other SDR, it is almost surely doing some frequency shifting before the sampler. Can you clarify what your setup is? – MBaz Jul 16 '19 at 23:35
• @MBaz Just update it – hevansa98 Jul 16 '19 at 23:38
• OK, so the SDR is doing band-pass filtering and frequency shifting. You shouldn't have any aliases. If you have any, they depend on which signals are in the passband of your BPF, and your intermediate frequency. – MBaz Jul 16 '19 at 23:40
• Look at this document if helps: aaronscher.com/wireless_com_SDR/RTL_SDR_AM_spectrum_demod.html – Fat32 Jul 17 '19 at 0:07
• Oh wow! Thank you! – hevansa98 Jul 17 '19 at 1:36