×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Multiple Conversion Receivers

Multiple Conversion Receivers

Multiple Conversion Receivers

(OP)
If I were to design a receiver for signals with carrier frequencies in the band from 15MHz to 65MHz and bandwidth 15kHz using an IF filter with center frequency of 455kHz, what range of frequencies would my local oscillator require in order to be capable of generating?

RE: Multiple Conversion Receivers

The frequency of the local oscillator does not determine the bandwidth, therefore the tuning range of the L.O. is the fundamental range, 15-65MHz, plus 455kHz. The bandwidth is determined entirely by the requency response of the I.F. filter/amplifier.

Note that due to the relatively poor "Q" of tuned L-C circuits of receiver front-ends at these sort of frequencies, most modern receiver designs use double-conversion techniques to ensure best selectivity.
 

RE: Multiple Conversion Receivers

With a such design, you'll get mirror signals. It means: Every received signal will appear on two places on your dial. Mixing products will be your local oscillator plus and minus IF (455 kHz). Frontal selectivity is not enough narrow to separate those two signals.
Much better results are reached using standard 10.7 MHz filters and detector circuits, there are lot of such filters, for wide band or narrow band FM on the market. NBFM filters have typicaly 16 KHz bandwidth. But I recomand you to read and learn some basic principles of receiving technology before you start to build something realy useful.
Good luck!

ulix +

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources