# IF frequency

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

1. ### thejimGuest

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. ### Anthony FremontGuest

You are about to answer it yourself. ;-)
Yes

3. ### Tom BiasiGuest

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

4. ### ArtGuest

Probably first convertor section of the navcom rcvr.

5. ### Peter BennettGuest

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) interchange.ubc.ca
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6. ### Phil AllisonGuest

"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 LaneGuest

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.

9. ### Phil AllisonGuest

"John Fields"
Peter Bennett

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

......... Phil

10. ### John FieldsGuest

---
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 AllisonGuest

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

** Try reading my post again.

More carefully this time.

........ Phil

12. ### John FieldsGuest

---
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 GriseGuest

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.

Thanks,
RIch

14. ### David HarmonGuest

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 AllisonGuest

"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 AllisonGuest

"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 SwiftGuest

Joining late:

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

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