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.

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

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

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

Frank GM0CSZ / KN6WH

J M Noeding wrote:
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.

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.

On Mon, 07 Mar 2005 11:13:33 GMT, "Highland Ham"
wrote:

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

Frank GM0CSZ / KN6WH

Nope, it is shown as
http://www.noding.com/la8ak/12345/images/bd34-rx.jpg
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
http://home.online.no/~la8ak/d28.htm

73, Jan-Martin LA8AK (ex GW5BFV)

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

J M Noeding wrote:

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 it be for dual diversity receive?

On Tue, 08 Mar 2005 11:19:00 -0600, Bob Liesenfeld
wrote:



J M Noeding wrote:

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 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

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