Measuring filter shape factor
 

On 11 Jan 2006 17:12:45 -0800, wrote:

Sine-wave measurements are more precise. My test is very close to real
life since it is testing the entire signal path, i.e. from antenna
input to audio output. I couldn't find the connector I made that taps
the line output, so I used the earphone output.

I have audio test gear that uses random noise with FFT analysis, in
addition to a swept sine. You always get more accurate results with a
swept sine. FFT analysis is only used when you need speed.

As you will notice from the graphical output, the noise floor is quite
high. I may do the test again BTW, you need a decent distortion
analyser for

I built one of those Heathkit H-P 334A clones. Took me 3 days. Had
to leave it behind when I resigned.

Measuring filter shape factor
 

On 11 Jan 2006 17:23:37 -0800, wrote:

At the time I did my test, I had a "hole" in my generators. The audio
gear went as high as 100k, and the RF gear went as low at 1Mhz, but the
IF was 455Khz. Hence I tested the whole audio path.

The impedances in the radio itself will effect the performance of the
filter, so there is something to be said for in-situ measurements.

Oh yeah, note that Abramoff didn't donate any money to the Democrats.

Read Rich Lowrie's latest editorial at National Review Online.

Measuring filter shape factor
 

Michael Thorpe wrote:
Amongst all these political propaganda posts, I wonder if there is a
little room for a technical question related to radio please?

If so, here goes:

How does one measure the IF filter shape factor in a shortwave radio?

I am technically minded and do have a signal generator, etc., but I am
not sure of the exact procedure. Do I get the audio level at the peak
frequency, then detune both sides off the peak for -3dB of the
demodulated audio, note down the width between these points, then
detune to obtain for -50dB of the demodulated audio, get the width at
these points, and then the ratio of the two widths is the filter shape
factor?

I would appreciate a link to the exact procedure if there is one
(don't seem to be able to find this in Google) or an expert advice
please.

I would also appreciate advice as to what actual values of filter
shape are considered poor, good, excellent, etc...

Thanks in advance,
Michael

Michael:
If you don't have a spectrum analyzer, you can use an oscope (setup for
x-y) while driving the filter (and x ) with a sweep function generator.
Remember that if you look at the IF output prior to the detector, you will
get a curve going positive and negative. If you look at the response after
the detector, it will look more like the IF filter shape that you expect.

--
Brian Denley
http://home.comcast.net/~b.denley/index.html

Measuring filter shape factor
 

wrote:

At the time I did my test, I had a "hole" in my generators. The audio
gear went as high as 100k, and the RF gear went as low at 1Mhz, but the
IF was 455Khz. Hence I tested the whole audio path.

The impedances in the radio itself will effect the performance of the
filter, so there is something to be said for in-situ measurements.

Oh yeah, note that Abramoff didn't donate any money to the Democrats.

LMFAO yet again at the Liberal 'tard boy!

dxAce
Michigan
USA

Measuring filter shape factor
 

check this page out:

http://www.radio-electronics.com/inf...electivity.php




"Michael Thorpe" wrote in message
news:43c4e407.4277000@news-server...
Amongst all these political propaganda posts, I wonder if there is a
little room for a technical question related to radio please?

If so, here goes:

How does one measure the IF filter shape factor in a shortwave radio?

I am technically minded and do have a signal generator, etc., but I am
not sure of the exact procedure. Do I get the audio level at the peak
frequency, then detune both sides off the peak for -3dB of the
demodulated audio, note down the width between these points, then
detune to obtain for -50dB of the demodulated audio, get the width at
these points, and then the ratio of the two widths is the filter shape
factor?

I would appreciate a link to the exact procedure if there is one
(don't seem to be able to find this in Google) or an expert advice
please.

I would also appreciate advice as to what actual values of filter
shape are considered poor, good, excellent, etc...

Thanks in advance,
Michael

Measuring filter shape factor
 

Good web page.....................I throw them on a network analyzer when I
want to measure them, but there are some pretty good ideas here.

Pete

"mike maghakian" wrote in message
...
check this page out:

http://www.radio-electronics.com/inf...electivity.php




"Michael Thorpe" wrote in message
news:43c4e407.4277000@news-server...
Amongst all these political propaganda posts, I wonder if there is a
little room for a technical question related to radio please?

If so, here goes:

How does one measure the IF filter shape factor in a shortwave radio?

I am technically minded and do have a signal generator, etc., but I am
not sure of the exact procedure. Do I get the audio level at the peak
frequency, then detune both sides off the peak for -3dB of the
demodulated audio, note down the width between these points, then
detune to obtain for -50dB of the demodulated audio, get the width at
these points, and then the ratio of the two widths is the filter shape
factor?

I would appreciate a link to the exact procedure if there is one
(don't seem to be able to find this in Google) or an expert advice
please.

I would also appreciate advice as to what actual values of filter
shape are considered poor, good, excellent, etc...

Thanks in advance,
Michael

Measuring filter shape factor
 

I'm a National Review subscriber. Really. However, I don't read the
on-line version as it is routinely disinformation, i.e. articles that
don't make it to the magazine. If you subscribe to the magazine, they
will print retractions of what appears online.

I will say at NR is the only conservative mag worth reading. They never
stooped to the level of say the Spectator.

David wrote:
On 11 Jan 2006 17:23:37 -0800, wrote:

At the time I did my test, I had a "hole" in my generators. The audio
gear went as high as 100k, and the RF gear went as low at 1Mhz, but the
IF was 455Khz. Hence I tested the whole audio path.

The impedances in the radio itself will effect the performance of the
filter, so there is something to be said for in-situ measurements.

Oh yeah, note that Abramoff didn't donate any money to the Democrats.

Read Rich Lowrie's latest editorial at National Review Online.

Measuring filter shape factor
 

On Wed, 11 Jan 2006 21:23:09 GMT, "Dale Parfitt"
wrote:


"Michael Thorpe" wrote in message
news:43c4e407.4277000@news-server...
Amongst all these political propaganda posts, I wonder if there is a
little room for a technical question related to radio please?

If so, here goes:

How does one measure the IF filter shape factor in a shortwave radio?

I am technically minded and do have a signal generator, etc., but I am
not sure of the exact procedure. Do I get the audio level at the peak
frequency, then detune both sides off the peak for -3dB of the
demodulated audio, note down the width between these points, then
detune to obtain for -50dB of the demodulated audio, get the width at
these points, and then the ratio of the two widths is the filter shape
factor?

I would appreciate a link to the exact procedure if there is one
(don't seem to be able to find this in Google) or an expert advice
please.

I would also appreciate advice as to what actual values of filter
shape are considered poor, good, excellent, etc...

Thanks in advance,
Michael


Hi Michael,

Although I have never given it much thought, I don't believe one can fully
characterize a filter while it is installed in the receiver- certainly,
parameters such as insertion loss would not be easily measurable. Perhaps
programs like Spectran may give some rough insight.
My method is classic- the filter is removed, properly terminated and
connected as the DUT on a scalar network analyzer.
If you have a vector network analyzer available you could also observe group
delay- an important factor in narrow filters.
See Paul Kiciak's (N2PK) site for his clever VNA- ideally suited for
filters.
Dale W4OP


Thanks, Dale, for your input. I would have no problems measuring
filters when taken out of a receiver. But this is not always possible,
for example with modern DSP software-defined receivers. There you have
no choice, the filter is no longer just a component you can desolder,
so you do need to measure the entire receiver. Parameters such as
insertion loss is immaterial in such cases - all that matters is the
filter shape.

Michael

Measuring filter shape factor
 

On 11 Jan 2006 14:14:01 -0800, wrote:

http://www.lazygranch.com/images/radio/cwfilter.gif
I did this test as follows:
1) radio in AM
2) AGC turned off
3) RF generator connector to antenna input
4) distortion analyzer connected to earphone output

Pick a frequency. I used 10Mhz. Set the RF generator and radio to that
frequency. Leave the radio dial alone. Sweep the RF generator manually
and measure the audio level from the distortion analyser. Plot the
results. This was a crystal filter, so you will need a RF generator
with 1Hz steps.

This is an in-situ measurement, i.e. this is not the same as just
testing the IF filter by itself. You need the distortion analyzer to
get the audio signal level independent from the noise.


Many thanks, this is interesting. What I am still unsure about is how
you determine the -6dB and -60dB points using the distortion analyzer:
When you say "measure the audio level", what exactly do you measure,
the audio signal fundamental (i.e. filtered at the modulation
frequency)?

So in fact you are only using the distortion analyzer to filter the
audio and to measure the level? I don't have a distortion analyzer,
but I guess I could simply use an oscilloscope or an audio spectrum
analyzer (PC sound card based).

Michael

Measuring filter shape factor
 

On 11 Jan 2006 21:06:53 -0800, wrote:

I'm a National Review subscriber. Really. However, I don't read the
on-line version as it is routinely disinformation, i.e. articles that
don't make it to the magazine. If you subscribe to the magazine, they
will print retractions of what appears online.

I will say at NR is the only conservative mag worth reading. They never
stooped to the level of say the Spectator.

David wrote:
On 11 Jan 2006 17:23:37 -0800, wrote:

At the time I did my test, I had a "hole" in my generators. The audio
gear went as high as 100k, and the RF gear went as low at 1Mhz, but the
IF was 455Khz. Hence I tested the whole audio path.

The impedances in the radio itself will effect the performance of the
filter, so there is something to be said for in-situ measurements.

Oh yeah, note that Abramoff didn't donate any money to the Democrats.

Read Rich Lowrie's latest editorial at National Review Online.

He says the Abramoff scandal is 100% Republicans.