Using non-overtone crystal in overtone mode?

This reminds me of a colleague who can easily tell everyone qualitatively that a situation deviates from theoretical ideals and as a result (using my words and not his) "$#!+ (poop) will splatter!" But he at least often in my experience have trouble saying this quantatively!

For one project, I decide to try something, and tell my boss what I am trying. This colleague of mine says (using words of mine and not his), "slop will spatter"! (As in light for adding optics to a light source for a specific application. This application has multiple LEDs shining onto an optical device with multiple elements.) Boss tells me that what I delivered to him and he found working should not have worked according to this colleague of mine, due to stray beams forming. So what do I do - I send photos to the boss of the beam pattern including the stray beams predicted by my colleague. I even named these stray beams after my colleague. But they were minor due to most light produced by the light source being on paths that resulted in adding to the desired beam combination as opposed to the undesired stray beams. Furthermore, my boss's industrial designer designed a baffling system that blocked the small amount of light from the multi-element light source that was on paths towards the stray beams as opposed to the desired rays that were "on course" to be utilized by the multi-elemt optical assembly as planned.

So beware that the situation may not be much worse than ideal when someone can tell you how you are deviating from ideal!

Now suppose someone makes a crystal oscillate in some overtone mode that the crystal manufacturer recommends against and is predicted to be "inharmonic" but turns out to be only a few hundred or even sometimes a few 10's of KHz from a multiple of a frequency that results from being used as directed?

As I said in different words in a different post - correctly predicting that $#!+ (AKA "slop") will spatter does not necessarily that much will spatter nor that any will spatter far, and maybe in many cases it is doubtful that both much will spatter and that much will spatter far.

- Don Klipstein ( snipped-for-privacy@misty.com)

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If it's not an integer multiple of the fundamental then it won't be a
harmonic.

A solid slab of crystal naturally oscillates at frequencies at which one of its three dimensions, length, breadth and thickness, is a mechanical

1/2-wavelength. It can easily be induced to oscillate at harmonics of the fundamental.

It can also oscillate in one of several mechanical modes, eg., longitudinal, breadth-wise or in torsion. And in shunt or series-resonant electrical modes.

The circuit it is embedded in can encourage a preferred frequency. It is easy to select harmonics. Self-preference is also given to the frequency which has the highest Q, ie., the least mechanical loss. This is usually the fundamental.

It does not oscillate EXACTLY at multiples simply because it has three dimensions and Length, Breadth and Thickness slightly 'interfere' with each other.

A poorly cut crystal, eg., lack of parallelism, at which there may be no strong preference may jump erratically between two non-harmonically related frequencies.

Frequency versus temperature curves depend on oscillation mode and on the angle at which the slab is cut relative to the direction of the individual crystals in the bulk material lattice as found by optical means. Cubic curves are best because they contain a flat horizontal portion.

An image rejecting mixer requires quadrature inputs (both signal and LO), two mixers, and summation of the outputs i.e.

sin(A+B) = sin(A)cos(B) + cos(A)sin(B)

Also - you're unlikely to have image problems at the second mixer.

Hi

have been examining some surplus mobile telephone base station equipment and discovered that the 70MHz to 455kHz mixers consists of

2x SA602. Since I've never seen an application using two such items, my guess it for an image rejection type mixer. Could somebody please guide me into some notes describing such mixer, possibly using 2x SA602 (and a crystal osc)

Jan-Martin

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J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

======================================= Jan-Martin , With 2xSA602 ,are you sure there isn't a 10.7 MHz 'intermediate' IF as well ?

Frank GM0CSZ / KN6WH

Nope, it is shown as

This for NMT450, while earlier NOKIA NMT900 mobile phone BS used

21.4Mz IF as well as 455kHz, while modern 900mc GSM handsets now are direct conversion. In the actual rig there is a 70MHz xtal filter as well as 455kHz ceramic filters The complete page (in Norwegian) is at 73, Jan-Martin LA8AK (ex GW5BFV)

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J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

Could it be for dual diversity receive?

there are 4 receivers, two on each board (with 2x SA604 and 4x SA602), so I think it is a lot of diversity if it was interesting

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J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm