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

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

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?

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?

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.

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

The distortion analyzer has a tracking bandpass filter. I'm using the
HP8903E, but for this purpose, even the 334B would do the trick. You
can use the analyzer to display the signal level of the sine wave
inpedentent of noise to the degree the bandpass filter can remove it.
[The 8903E reads amplitude, distortion, and frequency.]

I never reached the -60db point, because the signal was lost in the
noise. But you have to ask yourself, if the signal is in the noise, you
do care about the rejection?

In the dark ages, I was designing switched capacitor filters for modem
products. When you sold the chip as a Bell standard filter, you had to
implement that exact filter. However, the reality was the noise floor
and THD totally negated the effectiveness of the filter. [Power supply
rejection is a factor too.] So yeah, I could attenuate the alternate
(out of band) channel, but the filter noise was more significant than
what I was attenuating. Once the product became integrated, nobody
could see the filter implementation. The amount of filtering was
reduced to a level where the alternate channel (out of band) signal
level was minimum by picking a compromise between the number of poles
of filtering and the noise level of the amplifiers. Less poles of
filtering meant fewer all passes were required.

Now I'm not happy the noise floor of the radio crapped out at around
-45db. I don't know if measuring at the line outputs would have been
better. I need to do the measurement again.

It is quite possible that you can use your sound card to measure the
amplitude of the signal independent of the noise. BTW, I should have
mentioned I turned on the 1khz modulation on the RF signal generator.

My goal was to test a crystal filter I picked up at the flea market and
installed in my radio. [A good deal at $10.] One thing I learned is the
coupling capacitors make a difference in terms of the signal level. I'd
have to open the radio to see what I used, but I recall if the caps
were too small, the signal level was attenuated.


Michael Thorpe 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.


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

On 12 Jan 2006 12:00:25 -0800, wrote:

The distortion analyzer has a tracking bandpass filter. I'm using the
HP8903E, but for this purpose, even the 334B would do the trick. You
can use the analyzer to display the signal level of the sine wave
inpedentent of noise to the degree the bandpass filter can remove it.
[The 8903E reads amplitude, distortion, and frequency.]

I never reached the -60db point, because the signal was lost in the
noise. But you have to ask yourself, if the signal is in the noise, you
do care about the rejection?

Well I agree, but the point it is that I would like to be able to
compare my results to the actual manufactures' specifications of the
shape factor for various receivers. So if everyone defines the shape
factor as BW(-6dB)/BW(-60dB), then somehow I need to be able to
measure this. But I think I now have enough input from this group to
be able to do this. Thank you very much for your help.

In the dark ages, I was designing switched capacitor filters for modem
products. When you sold the chip as a Bell standard filter, you had to
implement that exact filter. However, the reality was the noise floor
and THD totally negated the effectiveness of the filter. [Power supply
rejection is a factor too.] So yeah, I could attenuate the alternate
(out of band) channel, but the filter noise was more significant than
what I was attenuating. Once the product became integrated, nobody
could see the filter implementation. The amount of filtering was
reduced to a level where the alternate channel (out of band) signal
level was minimum by picking a compromise between the number of poles
of filtering and the noise level of the amplifiers. Less poles of
filtering meant fewer all passes were required.

Now I'm not happy the noise floor of the radio crapped out at around
-45db. I don't know if measuring at the line outputs would have been
better. I need to do the measurement again.

It is quite possible that you can use your sound card to measure the
amplitude of the signal independent of the noise. BTW, I should have
mentioned I turned on the 1khz modulation on the RF signal generator.

My goal was to test a crystal filter I picked up at the flea market and
installed in my radio. [A good deal at $10.] One thing I learned is the
coupling capacitors make a difference in terms of the signal level. I'd
have to open the radio to see what I used, but I recall if the caps
were too small, the signal level was attenuated.


Michael Thorpe 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.


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

In article 43c63f8a.7487750@news-server,
(Michael Thorpe) 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.


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).

rkhalona gave you the right definition of shape factor and a web page
that explains it.

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

http://www.radio-electronics.com/inf...ty/selectivity.
php

The audio passband is often but not always defined at the IF stage with
a IF passband filter. The -6dB and -60dB is referenced to the filter
center IF frequency of 0dB. The filter is usually symmetrical and the SF
number refers to how fast the slope changes. Steeper is better. The -6dB
down point is usually considered the bandwidth of the filter.

With what you have the easiest thing to do would be to use the PC audio
spectrum analyzer. On a strong signal playing music use a max hold
function on the analyzer software and the passband of the filter should
become apparent. Look at where the high end response rolls off 6dB down
relative to what looks like a flat audio spectrum from low to middle
audio frequencies. Where the high frequencies roll of 6dB down from the
flat audio response range will be 1/2 the filter bandwidth.

For this to work the station you have are receiving must be have a wider
modulation bandwidth then you are using for an audio bandwidth filter so
this may only work for narrow filters.

If this does not work well enough then you will need an RF generator
that you can modulate at a frequency higher than the largest filter you
want to measure and use the PC analyzer as described above.

--
Telamon
Ventura, California

On Fri, 13 Jan 2006 04:47:07 GMT, Telamon
wrote:

In article 43c63f8a.7487750@news-server,
(Michael Thorpe) 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.


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).

rkhalona gave you the right definition of shape factor and a web page
that explains it.

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

http://www.radio-electronics.com/inf...ty/selectivity.
php

The audio passband is often but not always defined at the IF stage with
a IF passband filter. The -6dB and -60dB is referenced to the filter
center IF frequency of 0dB. The filter is usually symmetrical and the SF
number refers to how fast the slope changes. Steeper is better. The -6dB
down point is usually considered the bandwidth of the filter.

With what you have the easiest thing to do would be to use the PC audio
spectrum analyzer. On a strong signal playing music use a max hold
function on the analyzer software and the passband of the filter should
become apparent. Look at where the high end response rolls off 6dB down
relative to what looks like a flat audio spectrum from low to middle
audio frequencies. Where the high frequencies roll of 6dB down from the
flat audio response range will be 1/2 the filter bandwidth.

For this to work the station you have are receiving must be have a wider
modulation bandwidth then you are using for an audio bandwidth filter so
this may only work for narrow filters.

If this does not work well enough then you will need an RF generator
that you can modulate at a frequency higher than the largest filter you
want to measure and use the PC analyzer as described above.

--
Telamon
Ventura, California

Yep, that's a very good method, thanks! To refine this, I might use a
noise generator modulating a signal generator (instead of using a
station music). This should show the passband nicer and more steady, I
think.

I do have a signal generator, and I guess I could make a noise
generator using a Zener diode followed by an amplifier. Let's see...

Thanks again.

Michael