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IF frequency

Discussion in 'Electronic Basics' started by thejim, Jan 28, 2006.

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  1. thejim

    thejim Guest

    In an avionics book i read that the IF of a reiceiver is 29.05 Mhz.
    How does that figure come out?
    Does it come out by the difference between the incoming radio signal
    and the Local oscillator frequency?
    Am i saying it correctly?
  2. You are about to answer it yourself. ;-)
  3. Tom Biasi

    Tom Biasi Guest

    Just curious, where did you see that I.F. frequency mentioned?
  4. Art

    Art Guest

    Probably first convertor section of the navcom rcvr.
  5. I think I would put it another way around: The designer of the radio
    chose to use 29.05 MHz as the IF, and designed the IF amplifiers to
    pass that frequency. The frequency that the receiver will receive is
    that IF frequency plus (or minus) the local oscillator frequency.

    Peter Bennett, VE7CEI
    peterbb4 (at)
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  6. Phil Allison

    Phil Allison Guest

    "Peter Bennett"

    ** Much clearer.

    ** Err - not usually.

    Since the local oscillator is normally at a *higher* frequency than the IF
    frequency - the received frequency is the LO frequency plus or minus the
    IF frequency (single conversion assumed).

    ........ Phil
  7. Bruce Lane

    Bruce Lane Guest

    Yes to both questions.

    I would offer a minor spelling correction ('receiver' as opposed to
    'reiceiver'), and I would also say that 29.05 is only one example of an
    IF. It is by no means standard across all receivers.

    Example: Motorola has used IF's of 45MHz, 10.7MHz, and 17.9MHz in
    various land/mobile 2-way radio products. GE/Ericsson has used 10.7, and
    many others.

    There are still other receivers that use more than one IF (dual-
    conversion or triple-conversion).

    Happy reading.
  8. John Fields

    John Fields Guest

  9. Phil Allison

    Phil Allison Guest

    "John Fields"
    Peter Bennett

    ** That excludes those receivers where the IF is the sum of the received
    carrier and the LO.

    ......... Phil
  10. John Fields

    John Fields Guest

    Not so.

    Notice that he asked:

    "Does it come out by the difference between the incoming radio
    signal and the Local oscillator frequency?"

    If we choose an arbitry IF, say 10MHz, and we have a carrier of
    100MHz, then the LO can be either 110 MHz, whereupon the IF will be
    the difference between the 110MHz LO and the 100MHz carrier, or
    90MHz, where the LO will be the difference between the 100MHz
    carrier and the 90MHz LO.
  11. Phil Allison

    Phil Allison Guest

    "John Fields"
    'Phil Allison"
    ( snip bunch of irrelevant stuff )

    ** Try reading my post again.

    More carefully this time.

    ........ Phil
  12. John Fields

    John Fields Guest

    To what end?

    It's obvious that you didn't understand the OP's post in the first
    place, obviously don't understand heterodyning, and are trying to
    become argumentative for the purpose of changing the direction of
    the discussion away from could only end in your having to admit your
    ignorance of the subject.

    I'll have none of it.
  13. Rich Grise

    Rich Grise Guest

    He seems to think that it's common, or done at all, for the LO to be
    _added_ to the received frequency, resulting in an "IF" that's the _sum_
    of the frequencies.

    But, it is Phil Allison, after all.

  14. David Harmon

    David Harmon Guest

    On Mon, 30 Jan 2006 23:20:51 GMT in sci.electronics.basics, Rich
    I gather this system is used in premium wideband scanner designs so
    that image frequencies are far away and easily filtered out of the
    very high freq 1st IF.
  15. Phil Allison

    Phil Allison Guest

    "John Fields"
    "Phil Allison"

    ** So you might discover your error.

    If that is not it too *horrible* an experience.

    ** No is isn't.

    ........ Phil
  16. Phil Allison

    Phil Allison Guest

    "David Harmon"

    ** It is also done in some HF ( ie "communications" ) receivers for the
    same reason - where the first IF may be as high as 50 MHz.

    ......... Phil
  17. Steven Swift

    Steven Swift Guest

    Joining late:

    summing is also common in swept receivers (aka Spectrum Analyzers).
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