Greate insertion lost/

[Active8]

is it normal to have 150mv to 10 mv drop in a
10.633 Mhz ceramic 2 pole filter or is there something
wrong in carma ?
i know most ceramic resonators average 2..12 Db
insertion lost.
but in my head that RF voltage i am getting tends to
make me thing its not even worth calculating the
DB insertion difference..

That's a lot. Maybe the filter is mismatched to it's source/load.

 

[Active8]

Well. Now that I think about it, I'd expect the filter to be 10.7
MHz, not 10.633, but who knows WTF RS was up to with that radio.
Best you can do is (RS was pretty good at supplying service manuals
with schems, measurements, and all that. But that's one old radio
yer talking about. Maybe someone scanned it and it's on inet.)
figure out what the IF freq is supposed to be and test the
resonators out of circuit with a sig gen or just get some
replacements from muRata. Is the freq printed on them and what do
you mean by 2 pole and how do you know it's 2 pole. IIRC, the
resonators I've looked at lately were greater than 2 pole but it's
not something I paid much attention to.

IF there's 2 filters and each was say 12dB insertion loss, then
that's 24dB and is what your seeing with 150mV in 10mV out.

 

[Jamie]

is it normal to have 150mv to 10 mv drop in a
10.633 Mhz ceramic 2 pole filter or is there something
wrong in carma ?
i know most ceramic resonators average 2..12 Db
insertion lost.
but in my head that RF voltage i am getting tends to
make me thing its not even worth calculating the
DB insertion difference..

 

[Jamie]

or maybe its defective/deteriated and has shifted freq over time.
this unit is in a receiver that i been working on..
i take care of the major problem but notice the Receive
gain was very poor compared to what i think it should be.
i don't have a full service print for this unit so i have been
working hard using my Sg and RFm performing some calculations on
front end gain and IF passive gain.., i just happen to notice this
abnormally in the dual inline ceramic filter for the first IF stage.
why i noticed this is due to the fact that the strongest signal
i insert into the front end will only result in a 30% scale reading
of the receiver., i then inserted pass the pre'amp to find that i was
saturating the mixer stage which told me that something else was not
good beyond this point.
so the results ends up being a resonator that just does not seem to
be in spec.
i also noticed that as i spand the FM broadcast looking for comercial
signals i can receiving what appears to be digital serial noise all over
the place which tells me that the IF section must really be at full
sensitivity and thus receiving some out of band RF due to no apriciable
input signal to saturate the IF.
i did do a tempory by pass how ever of the resonators.
i then got FULL! scale readings on many broadcasts.
this unit is not my own but the owner does state that he has always
had trouble getting anything strong on the receiver from the day he
purchased it.
i think he got a lemon and never knew it.
))
this by the way is an old STA-90 Realistic Receiver..
about 23 years old.

 

[Fred Bloggs]

is it normal to have 150mv to 10 mv drop in a
10.633 Mhz ceramic 2 pole filter or is there something
wrong in carma ?
i know most ceramic resonators average 2..12 Db
insertion lost.
but in my head that RF voltage i am getting tends to
make me thing its not even worth calculating the
DB insertion difference..

That 10.633MHz resonator is your FM slope detector- the signal voltage
variation with frequency is peak detected to demodulate- therefore your
variation is not only normal but required.

 

[Active8]

That 10.633MHz resonator is your FM slope detector- the signal voltage
variation with frequency is peak detected to demodulate- therefore your
variation is not only normal but required.

Then it's really a quadrature detector. That makes sense.

 

[Fred Bloggs]

On Tue, 10 Feb 2004 13:48:57 GMT, [email protected] said...


Then it's really a quadrature detector. That makes sense.

A quadrature detector means the receiver demodulates I and Q signal
components- this is not the case for simple FM. The slope detector
method uses the fact that the high-Q bandpass frequency characteristic
is approximately linear with frequency around mid-slope to the center
frequency. The 10.7MHz IF is apparently there on a 10.633MHz center
frequency resonator- on its down side, so as the FM varies +/-50KHz ( or
whatever it is) about the 10.7MHz center, you end up with a
corresponding linear change in the output amplitude of the 10.633MHz
filter in proportion to that frequency variation- it is really a
controlled FM to AM conversion. This AM is then amplitude detected and
filtered to demodulate the signal.

 

[Active8]

On Tue, 10 Feb 2004 13:48:57 GMT, [email protected] said...


Then it's really a quadrature detector. That makes sense.

A quadrature detector means the receiver demodulates I and Q signal
components- this is not the case for simple FM. The slope detector
method uses the fact that the high-Q bandpass frequency characteristic
is approximately linear with frequency around mid-slope to the center
frequency. The 10.7MHz IF is apparently there on a 10.633MHz center
frequency resonator- on its down side, so as the FM varies +/-50KHz ( or
whatever it is) about the 10.7MHz center, you end up with a
corresponding linear change in the output amplitude of the 10.633MHz
filter in proportion to that frequency variation- it is really a
controlled FM to AM conversion. This AM is then amplitude detected and
filtered to demodulate the signal.
[/QUOTE]
Ah yes. The cos() cos(theta + 90) deal. In those old (read can't
get) Motorola NBFM chips there was a quad coil which was just a
tank except on those chips where IIRC they used a resonator and
that "quad coil" term threw me off. Head in wrong box.