×
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

local oscillator power

local oscillator power

local oscillator power

(OP)
How does local oscillator power effect sensitivity of a receiver?

RE: local oscillator power

The general rule for any superheterodyne receiver, either HF or radar, is that the local oscillator power must be sufficient to cause the mixer to run in its non-linear region of its transfer characteristics. That way you get the classic products of f0+LO and f0-LO at the I.F. output.

For microwave applications the modern method is to use a balanced mixer (one sideband output) or double-balanced mixer (upper and lower sideband on separate outputs). These designs are based on balanced half-bridge or full bridge arrangements of either diodes or FETs and these need a reasonable amount of LO power to get everthing biased correctly (at radar frequencies this can be anything up to +10dBm).

If you inject too much LO then weak signals get lost in the excess noise produced by the mixer. Conversely, too little signal gives problems with dynamic range and image rejection problems.

As you can probably guess, this means that for most mixers there is an optimum LO power range, so look at the manufacturer's data and choose a mixer design that has the best characteristics for your application.

RE: local oscillator power

The output amplitude is proportional with the LO amplitude
until maximum at saturation i.e. preferably use high
enough amplitude to assure saturation.


<nbucska@pcperipherals.com>

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