Measuring filter shape factor
 

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
 

Networksciences (original filter supplier for Drake) has a very
elaborate website on this subject. Try them first.

Measuring filter shape factor
 

"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

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


Look at the interstation atmospheric noise with a spectrum analyzer?

Measuring filter shape factor
 

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.

All that said, Bush should be impeached.

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

Measuring filter shape factor
 

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.

All that said, Bush should be impeached.

LMFAO at the misguided 'tard boy!

dxAce
Michigan
USA

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.

All that said, Bush should be impeached.

Can't you just use the random pink noise between stations, rather than
a sweep generator?

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

You need to generate a swept frequency response of the IF filter

Take a look at the following article on filter selectivity:

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

The shape factor is traditionally defined as

BW(-60dB)
SF =---------------
BW(-6dB)

(see the third figure in the article illustrating a typical filter
response and the meaning of the two bandwidths)

For an ideal filter (see second figure), this bandwidth ratio would be
equal to ONE (1.0).
The closer the shape factor is to 1.0, the sharper the selectivity. For
example, if you look at the specs for the Eton E1 on the following link
(Monitoring Times review)

http://www.monitoringtimes.com/html/...k-etone1xm.pdf

the shape factor for the 7 KHz filter would be:

SF = 12 KHz/7 KHz = 1.71 (not a very sharp filter, but not bad for a
radio of this type)

The other two filters have even worse shape factors. With DSP
receivers, these filters can be made extremely tight and shape factors
can be very close to 1.0.

Hope this is helpful. Perhaps Pete can chime in with a detailed
measurement procedure.

RK

Measuring filter shape factor
 

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

David wrote:
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.

All that said, Bush should be impeached.

Can't you just use the random pink noise between stations, rather than
a sweep generator?

Measuring filter shape factor
 

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.

rkhalona wrote:
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

You need to generate a swept frequency response of the IF filter

Take a look at the following article on filter selectivity:

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

The shape factor is traditionally defined as

BW(-60dB)
SF =---------------
BW(-6dB)

(see the third figure in the article illustrating a typical filter
response and the meaning of the two bandwidths)

For an ideal filter (see second figure), this bandwidth ratio would be
equal to ONE (1.0).
The closer the shape factor is to 1.0, the sharper the selectivity. For
example, if you look at the specs for the Eton E1 on the following link
(Monitoring Times review)

http://www.monitoringtimes.com/html/...k-etone1xm.pdf

the shape factor for the 7 KHz filter would be:

SF = 12 KHz/7 KHz = 1.71 (not a very sharp filter, but not bad for a
radio of this type)

The other two filters have even worse shape factors. With DSP
receivers, these filters can be made extremely tight and shape factors
can be very close to 1.0.

Hope this is helpful. Perhaps Pete can chime in with a detailed
measurement procedure.

RK