Intermediate Frequency choices

understand?

Carmen Sandiego?

Cheers

Phil Hobbs

Real men use zero IF.

John

Nah, you have to be biphasual to do that.

Cheers

Phil Hobbs

The other thing engineers forget about is high side versus low side mixing. Low side mixing reverses the spectrum, while high side doesn't.

..... Phil

understand?

Bipolar ;-)

...Jim Thompson

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s RF

understand?

=A0 =A0 =A0...Jim Thompson

Reversed spectrum isn't very good scrambling. It is used, but of course it is easily decoded. The funny thing is some speech is easily recognized when the spectrum is reversed. For instance, the word "Cadillac" can be heard when the spectrum is reversed because the mind also tunes into the cadence of speech.

There is a version of frequency inversion where the carrier is moved based on a predetermined code. This is generlly called rolling code frequency inversion. Better than the static case, but digital schemes are much more effective than simple mixers.

Designate the input signal FL and FH, where FH>FL. Let the carrier be FC. Sidebands are: FC-FH to FC-FL FC+FL to FC+FH

The higher band signal, i.e. (FC+FL) to (FC+FH) does not reverse the spectrum.

I think that you are confusing IF filter selectivity and front end selectivity.

That refers to the IF filter bandwidth.

This has to do with the front end (preselector) filter design.

By moving the image frequency as far away from the desired frequency as possible will simplify the front end filter design. A lower Q is required in a tunable front end and even one octave wide fixed preselctor filter can sometimes be used (with a sufficiently strong mixer :-).

Paul

"Phil Allison"

Designate the input signal FL and FH, where FH>FL. Let the carrier be FC. Sidebands are: FC-FH to FC-FL FC+FL to FC+FH

The higher band signal, i.e. (FC+FL) to (FC+FH) does not reverse the spectrum.

You are one totally INSANE moron !!

FYI:

Low side mixing is where the LO is **below** the incoming RF !!!!!

So, if the RF frequency increases while the LO stays the same, the IF frequency goes up.

QED.

.... Phil

Have a nice day Phil. Oh wait, people like you never have a nice day.

Lowering the required Q is a good thing. The design is less sensitive to process.

--- No, the image frequency is the desired RF signal + twice the LO.

For example, the right way:

1. Desired signal: 1030 MHz LO: 1090 MHz IF: 60 MHz

1. Image: 1150 MHz (1030 MHz + (2 * 60 MHz)) LO: 1090 MHz IF: 60 MHz

Your way:

1. Desired signal: 1030 MHz LO: 1090 MHz IF 60 MHz

1. "Image" 1: 1090 MHz (1030 MHz + 60 MHz) LO: 1090 MHz IF-: 0 Hz IF+ 2180 MHz

2. "Image" 2: 970 MHz (1030 MHz - 60 MHz) LO: 1090 MHz IF-: 120 MHz IF+: 2060 MHz Where IF+ and IF- are the sum and difference products out of the mixer and into the IF amp.

"John Fields"

The " image frequency" may be above or below the wanted RF carrier.

You completely failed to see the IMPLICATION of the name - you pathetic dope !!!!

But there was a typo in my post.

Correction:

The "image frequency" is that frequency obtained by adding or subtracting the IF frequency to or from the LO frequency.

Naturally - one adds or subtracts depending on whether the particular design has the LO set above or below the RF frequency.

.... Phil

understand?

GARy Burrell and MIN Kao

I designed the analog portions of three of their GPS chips.

...Jim Thompson

understand?

The engineer was eating taffy when he was asked what to call it?

Ed

You can do the spur calculation on PAPER, with nothing more than a freaking PENCIL and a functioning BRAIN.

Writing one is as easy as pie, however, and takes much of the tedium (and dropped minus signs) out of the process.

There are some regularities in the amplitudes that a small program can help with, though--especially the difference in the falloff vs order of LO and RF harmonics. If a spur is at N*f_LO+M*f_RF, its amplitude falls of more slowly with N than with M because the LO is usually driven much harder.

Cheers

Phil Hobbs

They were looking 6 or 7 intermods out ;-)

...Jim Thompson