In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

7. It has been suggested that using a 2 MHz IF frequency would allow
wider bandwidth than the standard 455 kHz IF frequency. I fail to
see why
this should be true.

Because for the same Q value, the pass band would be 4 times wider

Where is it written that the same loaded Q must be used for both filters?
If you can change the center frequency, why can't you change the loaded Q?

The lower the Q, the more IFTs required for a given amount of pass band and
attenuationout of band.

Patrick, you are missing the point, the issue was the merits of a 2.0 MHz
IF frequency vs. a 455 kHz IF frequency with respect to
bandwidth/selectivity, my point was that for the sort of bandwidths we are
talking about for audio, a 455 kHz IF can provide virtually identical
"pass band and attenuation out of band" with exactly the same number of
IFTs as a 2.0 MHz IF frequency. The loaded Qs result from the design
specifications in both cases, and are what they are. There may be
architectural advantages to using one or the other IF frequency in a
radio, but so far only the bandwidth/selectivity has been mentioned and in
that regard an IF of 2.0 MHz offers no significant advantage over a 455
kHz IF for the reception of the full audio bandwidth.

To illustrate this consider the example of the following calculated
response curves for both a 455 kHz IFT and a 2.0 MHz IFT:

One One
455 kHz IFT 2.0 MHz IFT
Q = 15.167 Q = 66.667

Fc-60 kHz -24.30 dB -24.18 dB
Fc-50 kHz -21.22 dB -21.09 dB
Fc-40 kHz -17.56 dB -17.42 dB
Fc-30 kHz -13.22 dB -13.07 dB
Fc-20 kHz -8.72 dB -8.60 dB
Fc-15 kHz -7.09 dB -7.02 dB
Fc-10 kHz -6.27 dB -6.24 dB
Fc-05 kHz -6.04 dB -6.04 dB
Fc kHz -6.02 dB -6.02 dB
Fc+05 kHz -6.03 dB -6.03 dB
Fc+10 kHz -6.19 dB -6.22 dB
Fc+15 kHz -6.86 dB -6.96 dB
Fc+20 kHz -8.34 dB -8.50 dB
Fc+30 kHz -12.75 dB -12.95 dB
Fc+40 kHz -17.15 dB -17.32 dB
Fc+50 kHz -20.88 dB -21.01 dB
Fc+60 kHz -24.01 dB -24.12 dB

The only advantage the 2.0 MHz IFT shows is marginally better symetry of
responce about the ceter frequency, the response of the two IFTs is
virtually identical.

Within reason, for bandwidths typical of audio
receivers, you should be able to build a filter at 455 kHz that has
effectively the same response as a 2 MHz filter. There is no need to
throw out the 455 kHz IF just to get wide bandwidth.

Its difficult to make a 455kHz typical old IFT produce a nice flat topped
20 kHz wide BW. Its either pointy nosed, undecoupled, or flat
topped, critical
coupled,
or over critical or rabbit eared.
I have tried all that.

So you have tried all that and rejected the "pointy nosed", "flat topped",
and "rabbit eared" response curves. I am left to wonder what sort of
response curve you were looking for? Why not settle for a nice "flat
topped" response curve and be done with it?

I didn't say I had rejected the flat topped critical coupled IF response.

Then what did you say? You said you had "tried all that" but now it
appears that you were telling a little fib and hadn't actually tried a 455
kHz IF designed to produce the desired response.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

7. It has been suggested that using a 2 MHz IF frequency would allow
wider bandwidth than the standard 455 kHz IF frequency. I fail to
see why
this should be true.

Because for the same Q value, the pass band would be 4 times wider

Where is it written that the same loaded Q must be used for both filters?
If you can change the center frequency, why can't you change the loaded Q?

The lower the Q, the more IFTs required for a given amount of pass band and
attenuationout of band.

Patrick, you are missing the point, the issue was the merits of a 2.0 MHz
IF frequency vs. a 455 kHz IF frequency with respect to
bandwidth/selectivity, my point was that for the sort of bandwidths we are
talking about for audio, a 455 kHz IF can provide virtually identical
"pass band and attenuation out of band" with exactly the same number of
IFTs as a 2.0 MHz IF frequency. The loaded Qs result from the design
specifications in both cases, and are what they are.

Sure. But the same Q would give wider BW at 2 MHz.
I have not ever done this, so I guess at what the final response could be.



There may be
architectural advantages to using one or the other IF frequency in a
radio, but so far only the bandwidth/selectivity has been mentioned and in
that regard an IF of 2.0 MHz offers no significant advantage over a 455
kHz IF for the reception of the full audio bandwidth.

I supect it might, and one article in Wireless World refered to using
10.7 MHz.



To illustrate this consider the example of the following calculated
response curves for both a 455 kHz IFT and a 2.0 MHz IFT:

One One
455 kHz IFT 2.0 MHz IFT
Q = 15.167 Q = 66.667

Fc-60 kHz -24.30 dB -24.18 dB
Fc-50 kHz -21.22 dB -21.09 dB
Fc-40 kHz -17.56 dB -17.42 dB
Fc-30 kHz -13.22 dB -13.07 dB
Fc-20 kHz -8.72 dB -8.60 dB
Fc-15 kHz -7.09 dB -7.02 dB
Fc-10 kHz -6.27 dB -6.24 dB
Fc-05 kHz -6.04 dB -6.04 dB
Fc kHz -6.02 dB -6.02 dB
Fc+05 kHz -6.03 dB -6.03 dB
Fc+10 kHz -6.19 dB -6.22 dB
Fc+15 kHz -6.86 dB -6.96 dB
Fc+20 kHz -8.34 dB -8.50 dB
Fc+30 kHz -12.75 dB -12.95 dB
Fc+40 kHz -17.15 dB -17.32 dB
Fc+50 kHz -20.88 dB -21.01 dB
Fc+60 kHz -24.01 dB -24.12 dB

The only advantage the 2.0 MHz IFT shows is marginally better symetry of
responce about the ceter frequency, the response of the two IFTs is
virtually identical.

The equality in performance depends on a large Q difference, with
544 kHz Q much lower than 2MHz Q to get the same BW.

The Q of a typical 455 kHz IFT is higher than you have indicated, because
the impedance of the LC circuit at Fo is required to be high to suit
pentode loading, and to get high gain.

If the Q was real low, and hence the Fo impedance, you
would probably need 3 IFTs.

I have never tried 3 very damped IFTs.




Within reason, for bandwidths typical of audio
receivers, you should be able to build a filter at 455 kHz that has
effectively the same response as a 2 MHz filter. There is no need to
throw out the 455 kHz IF just to get wide bandwidth.

Its difficult to make a 455kHz typical old IFT produce a nice flat topped
20 kHz wide BW. Its either pointy nosed, undecoupled, or flat
topped, critical
coupled,
or over critical or rabbit eared.
I have tried all that.

So you have tried all that and rejected the "pointy nosed", "flat topped",
and "rabbit eared" response curves. I am left to wonder what sort of
response curve you were looking for? Why not settle for a nice "flat
topped" response curve and be done with it?

I didn't say I had rejected the flat topped critical coupled IF response.

Then what did you say? You said you had "tried all that" but now it
appears that you were telling a little fib and hadn't actually tried a 455
kHz IF designed to produce the desired response.

What I said was what I said.
You are confused.

Build a radio with 2MHz and measure it, maybe it works better.

Just don't knock the idea before trying it, or condemn the idea
with postulations about what might be.
These things must be tried and measured, to really know.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

Patrick, you are missing the point, the issue was the merits of a 2.0 MHz
IF frequency vs. a 455 kHz IF frequency with respect to
bandwidth/selectivity, my point was that for the sort of bandwidths we are
talking about for audio, a 455 kHz IF can provide virtually identical
"pass band and attenuation out of band" with exactly the same number of
IFTs as a 2.0 MHz IF frequency. The loaded Qs result from the design
specifications in both cases, and are what they are.

Sure. But the same Q would give wider BW at 2 MHz.
I have not ever done this, so I guess at what the final response could be.

But so what, I thought we were talking about IFs for audio here, not video
IFs? For an audio receiver I would think at the most we would want a 40
kHz bandwidth, more likely 30 kHz, or even 20 kHz in the US where the FCC
effectively limits the audio bandwidth to 10 kHz? What exactly do you see
as the advantage of a 2.0 MHz IF in an AM broadcast receiver?

The way I see it both 455 kHz IFs and 2.0 MHz IFs can be built with the
bandwidth necessary for High Fidelity AM audio reception. The stage gains
will be virtually identical for both the 455 kHz IFs and 2.0 MHz IFs of
similar bandwidth, with the exact stage gain depending somewhat on design
choices and practicalities. The wideband 455 kHz IF will have lower stage
gain than a normal narrow 455 kHz IF, but the 2.0 MHz IF also suffers from
lower stage gain. The wideband 455 kHz IF has the advantage that standard
RF front-end components like tuning capacitors and oscillator coils can be
used, while the 2.0 MHz IF will require special RF components.

What exactly are the advantages of a 2.0 MHz IF from a
selectivity/bandwidth point of view?

There may be
architectural advantages to using one or the other IF frequency in a
radio, but so far only the bandwidth/selectivity has been mentioned and in
that regard an IF of 2.0 MHz offers no significant advantage over a 455
kHz IF for the reception of the full audio bandwidth.

I supect it might, and one article in Wireless World refered to using
10.7 MHz.

Certainly a high IF frequency will have advantages in image response, but
if the bandwidth is the same, the audio quality should be similar. What
exactly did Wireless World say was so great about using a 10.7 MHz IF for
a MW AM receiver? Wireless World is a hobbyist magazine and all their
authors are not necessarily up to speed, although in the old days they
often did have articles by people who knew what they were talking about
with respect to radios. I suspect that the reason Wireless World might
have used a 10.7 MHz IF in a MW AM broadcast receiver is because it was an
easy way for a hobbyist, who both doesn't have a clue what he is doing,
and doesn't have the necessary test equipment, to get a super wide
bandwidth.

To illustrate this consider the example of the following calculated
response curves for both a 455 kHz IFT and a 2.0 MHz IFT:

The only advantage the 2.0 MHz IFT shows is marginally better symetry of
responce about the ceter frequency, the response of the two IFTs is
virtually identical.

The equality in performance depends on a large Q difference, with
544 kHz Q much lower than 2MHz Q to get the same BW.

Yes, although I have some reservations about the use of the term "Q", that
is obvious, but so what, what difference does it make?

The Q of a typical 455 kHz IFT is higher than you have indicated, because
the impedance of the LC circuit at Fo is required to be high to suit
pentode loading, and to get high gain.

You also are going to sacrifice stage gain in the same way with a 2.0 MHz
IF, so this is no more of a problem for the wideband 455 kHz IF than for
the 2.0 MHz IF.

If the Q was real low, and hence the Fo impedance, you
would probably need 3 IFTs.

This is a consequence of the wide bandwidth, not the IF frequency, the
problem is identical at 2.0 MHz.

I have never tried 3 very damped IFTs.

The fact that you haven't tried something doesn't prove anything one way
or the other. Also, what does "damped" mean in this context? I would
have to do some research, but I suspect that "damping" is more related to
filter bandwidth than to the center frequency, and both filters are aiming
for the same bandwidth.

What I said was what I said.
You are confused.

Maybe, in what way are you suggesting I am confused? I would suggest to
you that you don't understand how to design an IF filter, and don't
understand what can be done at 455 kHz.

Build a radio with 2MHz and measure it, maybe it works better.

You are the 2.0 MHz IF advocate not me, you still haven't suggested any
reason why it might work better from a bandwidth/selectivity standpoint?

Just don't knock the idea before trying it, or condemn the idea
with postulations about what might be.

I'm not, I know it would work, what I don't understand is what the
advantages are over a 455 kHz IF of the same bandwidth? You are not
explaining yourself, cite some concrete facts.

These things must be tried and measured, to really know.

While I can't claim to have designed the filter I used, I have actually
built a transistor superhetrodyne AM tuner using a 455 kHz block filter
with a 30 kHz IF bandwidth. Will the 2.0 MHz IF work better than this?
Have you tried a properly designed wideband 455 kHz IF filter to see how
it worked? The filter I used came out of a 2-way land mobile radio and I
think it was about an 8 pole filter. Back in the old days of land mobile
here in the US, wider channels with greater bandwidth were used than are
used today. Over time the channels were squeezed down to accommodate
additional channels in the same space, and block filters of several
different bandwidths were available to suit the changing allocations and
operating frequencies.

I have also built wideband single frequency TRF receivers using modified
double tuned IF transformers.

So what it boils down to is that you haven't tried a wideband 455 kHz
filter while I have, and I haven't tried a 2.0 MHz IF filter, which you
may or may not have done. I at least have cited some concrete facts about
IF filters, while you have only muttered about Q, without indicating how
it actually relates to the problem. I am not a "filter jock" (tm) but I
think it is generally desirable that the Q of the components used in a
filter be high, especially when we get beyond simple double tuned
transformers. What you are calling Q is more related to how the filter is
terminated, which is a different matter than the Q of the components that
make up the filter.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

John Byrns wrote:
What exactly are the advantages of a 2.0 MHz IF from a
selectivity/bandwidth point of view?

Both pros and cons to this John.

Since the bandwidth is a percentage of the center frequency,
the shape of the bandwidth will change based on the distance
from the center frequency (as a percentage.)

Assuming just for the moment +/- 5 KHz.
At 455 KHz that's about 1% above and below.
At 2 MHz, that's now only .25% above and below.

As you get further from the center frequency, percentage
wise, the shape of the curve as it transitions from inside
to outside of the band pass is going to look different at
the upper frequency than it does at the lower frequency.

Certainly a high IF frequency will have advantages in image response, but
if the bandwidth is the same, the audio quality should be similar.

With the notable exception of the difference in shape of the
roll off above and below the center frequency.

In the world of designing filters (and overall system performance)
this is called group delay. A shorter, perhaps more recognizable
term would be linear phase shift over the entire band pass of the
filter.

Wireless World is a hobbyist magazine and all their
authors are not necessarily up to speed

They were under the same constraints as the Weekly World News.
"If it wasn't true, they couldn't print it." Note smiley face
here. ;-)

Yes, although I have some reservations about the use of the term "Q", that
is obvious, but so what, what difference does it make?

Back to the original comments about Q. In a perfect world, it
would only be a matter of the LC ratio setting the bandwidth
of a tuned circuit. Of courses, there are other things that
get in the way to reduce the overall Q of a circuit. Nasty
little things like the series resistance of the coils, dielectric
losses in both the coil forms and capacitor insulation material.

Back to the original "ideal" values of Q. 15 at 455 KHz and
67 at 2 MHz. It is physically "more challenging" to get higher
Q at a higher frequency. All of the various losses of the
components tend to get in the way. Wire losses, dielectric
losses and any losses of the ferrite used in the core materials.

Also, what does "damped" mean in this context? I would
have to do some research, but I suspect that "damping" is more related to
filter bandwidth than to the center frequency, and both filters are aiming
for the same bandwidth.

"Damped" means adding some form of resistance across the reactive
components of a circuit. As an example, if you were to assemble a
nice 455 KHz IF transformer and found that the bandwidth was too
narrow, a fast method of widening it would be to place parallel
resistors across the windings.

Another point about "damped" is that if a tuned circuit has too
high a Q, a sudden transient will tend to make it oscillate.
In communications receivers, this is obvious that a signal sounds
more like you're ringing a bell, than simply turning a tone on
and off. (Kind of like using the sustain pedal on a piano.)

Maybe, in what way are you suggesting I am confused? I would suggest to
you that you don't understand how to design an IF filter, and don't
understand what can be done at 455 kHz.

Lets not go in that direction.

An IF transformer is simply a two pole butter worth filter.
That it can have different input and output impedance just
makes it really convenient for taking the source from a plate
and connecting it to a grid for a load.

By definition, a butter worth filter has a smooth curve with
only one peak (in the middle.) And the shape (steepness) of
the band pass is related to the overall Q of the circuit.

The next type of filter, would be Chebychev, This is no more
than a "predistorted" butter worth filter network. By allowing
a certain amount of ripple in the pass band, the shape of the
rejection can be made sharper. The obvious trade off is the
amount of distortion to the signal within the pass band.

A simple example of this would be stagger tuned IF coils.
Two or more peaks, and a dip (or dips), ripple, in the middle.

While I can't claim to have designed the filter I used, I have actually
built a transistor superhetrodyne AM tuner using a 455 kHz block filter
with a 30 kHz IF bandwidth. Will the 2.0 MHz IF work better than this?
Have you tried a properly designed wideband 455 kHz IF filter to see how
it worked? The filter I used came out of a 2-way land mobile radio and I
think it was about an 8 pole filter.

The point you've probably overlooked in land mobile operations is that
it was NEVER designed as a "hi-fi" system. There's a reason for the
term "voice grade." Having as much a 3 dB of ripple in a band pass
filter is meaningless especially when the filter is in the midst of
a limiting IF strip for FM recovery, and on AM demodulation. What
really matters here is limiting the bandwidth of the received signal to
ONLY include that of the wanted (in channel) information and none of
the unwanted (adjacent channel) information to get to the discriminator.

So what it boils down to is that you haven't tried a wideband 455 kHz
filter while I have, and I haven't tried a 2.0 MHz IF filter, which you
may or may not have done. I at least have cited some concrete facts about
IF filters, while you have only muttered about Q, without indicating how
it actually relates to the problem. I am not a "filter jock" (tm) but I
think it is generally desirable that the Q of the components used in a
filter be high, especially when we get beyond simple double tuned
transformers. What you are calling Q is more related to how the filter is
terminated, which is a different matter than the Q of the components that
make up the filter.

You should take the time to read up on "filter jockeying" John.
You're making a lot of incorrect assumptions on how they work.

The primary requirement on the Q of individual components in
filter design is only such that their value of Q be high enough
to not materially effect the overall Q of the circuit. As an
example, (and without getting into cryogenic treatments and
styrofoam cups) A speaker system sounds better through 25 feet
of #12 AWG wire than it does through 25 feet of #18 AWG wire.
And that's strictly due to the resistive loss of the wire in
comparison to the losses in the actually speaker design and
implementation.

I had a electronics instructor in college that would show you
"The secret of electronics" that he kept hidden, and locked,
inside a small jewelry box if you "caught on" during his course.

With some fanfare, he would slowly open the box and you would
see an inductor, a resistor and a capacitor.

And it's really just that simple. What gets complicated is when
you forget that all three items have hidden values of the others
contained within them. (I.e. the difference between practical
and theoretical parts.)

Jeff



--
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." Benjamin Franklin
"A life lived in fear is a life half lived."
Tara Morice as Fran, from the movie "Strictly Ballroom"

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

Patrick, you are missing the point, the issue was the merits of a 2.0 MHz
IF frequency vs. a 455 kHz IF frequency with respect to
bandwidth/selectivity, my point was that for the sort of bandwidths we are
talking about for audio, a 455 kHz IF can provide virtually identical
"pass band and attenuation out of band" with exactly the same number of
IFTs as a 2.0 MHz IF frequency. The loaded Qs result from the design
specifications in both cases, and are what they are.

Sure. But the same Q would give wider BW at 2 MHz.
I have not ever done this, so I guess at what the final response could be.

But so what, I thought we were talking about IFs for audio here, not video
IFs? For an audio receiver I would think at the most we would want a 40
kHz bandwidth, more likely 30 kHz, or even 20 kHz in the US where the FCC
effectively limits the audio bandwidth to 10 kHz? What exactly do you see
as the advantage of a 2.0 MHz IF in an AM broadcast receiver?

Its a lot easier to get a wider pass band of 30 kHz with 2MHz IFTs than with
455 kHz IFTs.
Try it some time, and then you'll know.



The way I see it both 455 kHz IFs and 2.0 MHz IFs can be built with the
bandwidth necessary for High Fidelity AM audio reception. The stage gains
will be virtually identical for both the 455 kHz IFs and 2.0 MHz IFs of
similar bandwidth, with the exact stage gain depending somewhat on design
choices and practicalities. The wideband 455 kHz IF will have lower stage
gain than a normal narrow 455 kHz IF, but the 2.0 MHz IF also suffers from
lower stage gain. The wideband 455 kHz IF has the advantage that standard
RF front-end components like tuning capacitors and oscillator coils can be
used, while the 2.0 MHz IF will require special RF components.

What exactly are the advantages of a 2.0 MHz IF from a
selectivity/bandwidth point of view?

I suspect 3 x 2MHz IFTs would be easier to get a flat topped
pass band and sufficient steep roll off just outside the band.

I also suspect any old 455 kHz IFTs could easily
have about 3/4 of their turns removed, and retain the same
caps of 250pF.

For 250pF, to get 455 kHz, one needs 0.48 mH

For 250pF, and 2 MHz, one needs 0.025 mH.

To reduce L by 20 times, the turns would need reducing
by a factor of 1/4.47.

Thus the DCR would fall, and Q could rise.

I have used ex IFT windings with turns removed for
high Q RF input coils on my reciever, to get the range of
tuning required between 500 and 1750 kHz with a
20 pF to 360 pF tuning gang.
The ferrite slug is retained.

The wire is litz wire, with low RF resistance, hence it gives a high Q,
but for 2 mHz, solid round wire would probably be OK, like in 4.5 MHz
TV IFTs and 10.7 MHz FM IFTs.

HF IFTs are easier to wind than 455 kHz.



There may be
architectural advantages to using one or the other IF frequency in a
radio, but so far only the bandwidth/selectivity has been mentioned and in
that regard an IF of 2.0 MHz offers no significant advantage over a 455
kHz IF for the reception of the full audio bandwidth.

I supect it might, and one article in Wireless World refered to using
10.7 MHz.

Certainly a high IF frequency will have advantages in image response, but
if the bandwidth is the same, the audio quality should be similar. What
exactly did Wireless World say was so great about using a 10.7 MHz IF for
a MW AM receiver?

Wide AF response was easily achieved.

Wireless World is a hobbyist magazine and all their
authors are not necessarily up to speed, although in the old days they
often did have articles by people who knew what they were talking about
with respect to radios.

I differ. WW and what it became, Electronics World wasn't just an
amateur's magazine. It had cutting edge articles about electronics
from 1917 onwards, and I suggest you park yourself beside a
pile of all the old copies and have a good read.
Most of the info was only comprehensible by very well university educated
professionals, or intellectuals, and most ideas were backed up with mathematical
proofs which nearly all the general public couldn't understand.



I suspect that the reason Wireless World might
have used a 10.7 MHz IF in a MW AM broadcast receiver is because it was an
easy way for a hobbyist, who both doesn't have a clue what he is doing,
and doesn't have the necessary test equipment, to get a super wide
bandwidth.

I leave you to your suppositions.



To illustrate this consider the example of the following calculated
response curves for both a 455 kHz IFT and a 2.0 MHz IFT:

The only advantage the 2.0 MHz IFT shows is marginally better symetry of
responce about the ceter frequency, the response of the two IFTs is
virtually identical.

The equality in performance depends on a large Q difference, with
544 kHz Q much lower than 2MHz Q to get the same BW.

Yes, although I have some reservations about the use of the term "Q", that
is obvious, but so what, what difference does it make?

Build a receiver, and find out.



The Q of a typical 455 kHz IFT is higher than you have indicated, because
the impedance of the LC circuit at Fo is required to be high to suit
pentode loading, and to get high gain.

You also are going to sacrifice stage gain in the same way with a 2.0 MHz
IF, so this is no more of a problem for the wideband 455 kHz IF than for
the 2.0 MHz IF.

Use more stages if stage gain is low.
The EA design used 3 IFTs, with two j-fet IF amps, with quite
heavily damped 455 kHz IF coils.




If the Q was real low, and hence the Fo impedance, you
would probably need 3 IFTs.

This is a consequence of the wide bandwidth, not the IF frequency, the
problem is identical at 2.0 MHz.

I have never tried 3 very damped IFTs.

The fact that you haven't tried something doesn't prove anything one way
or the other.

It means that what you or I am saying may not include all the facts about
the subject. Build and measure will give the facts.

Also, what does "damped" mean in this context?

Strapping resistance across the LC tuned circuit to reduce the Q.
The rate of attenuation just either side of the pass band becomes
much less, so more IF stages must be used.

I would

have to do some research, but I suspect that "damping" is more related to
filter bandwidth than to the center frequency, and both filters are aiming
for the same bandwidth.

Damping reduces Q, and increases BW.
But it also reduces Z at Fo, thus reducing gain in an amp
which must be a current source, like a pentode or j-fet,
to realise the best selectivity for the LC circuit.



What I said was what I said.
You are confused.

Maybe, in what way are you suggesting I am confused? I would suggest to
you that you don't understand how to design an IF filter, and don't
understand what can be done at 455 kHz.

I know enough about IFT design, after having built my own radio.


Build a radio with 2MHz and measure it, maybe it works better.

You are the 2.0 MHz IF advocate not me, you still haven't suggested any
reason why it might work better from a bandwidth/selectivity standpoint?

I refuse to repeat myself any further.



Just don't knock the idea before trying it, or condemn the idea
with postulations about what might be.

I'm not, I know it would work, what I don't understand is what the
advantages are over a 455 kHz IF of the same bandwidth? You are not
explaining yourself, cite some concrete facts.

I have already stated that for a given Q, the pass band for a 2MHz IFT
is naturally a lot wider than for a 455 kHz IFT.

Put it this way, if you make IFTs of 100 kHz, then its all the harder to get
a flat topped bandpass response which is 20 kHz wide, with
high sloped skirt response each side.



These things must be tried and measured, to really know.

While I can't claim to have designed the filter I used, I have actually
built a transistor superhetrodyne AM tuner using a 455 kHz block filter
with a 30 kHz IF bandwidth.

Ceramic filters are another way to achieve the same bandpass filter
that the IFT could do.
But they were never used in tube sets for the BCB.


Will the 2.0 MHz IF work better than this?

I suspect yes, but getting a 2 MHz cermic filter with 30 kHz of BW might be
unobtainium.


Have you tried a properly designed wideband 455 kHz IF filter to see how
it worked?

Yes, and trying to squeeze 20 kHz of flat topped BW was difficult with stock IFTs.

I have already said what my solution was, to use a variable distance coils and
some damping
on IFT no1, which allowed me to have only 2 IFTs, and 1 IF amp, a 6BX6, fixed
bias,
for low thd IF amplification.

The filter I used came out of a 2-way land mobile radio and I
think it was about an 8 pole filter. Back in the old days of land mobile
here in the US, wider channels with greater bandwidth were used than are
used today. Over time the channels were squeezed down to accommodate
additional channels in the same space, and block filters of several
different bandwidths were available to suit the changing allocations and
operating frequencies.

I have also built wideband single frequency TRF receivers using modified
double tuned IF transformers.

One of the Electronics Australia kit designs I have used
a two stage TRF design with highish Q LC, with stagger tuning
at the low F part of the band. This utilised having mutual capacitive
coupling of the Ls in their earthy ends to ground via one common 0.1 uF.
I couldn't easily reproduce the nice response curves of the kit set,
and it was not good enough to give selectivity between locals
here where I wanted to hear a 300 watt station which was only
45 kHz away from a 5,000 watt station.
But otherwise, the TRF was a fine performer.



So what it boils down to is that you haven't tried a wideband 455 kHz
filter while I have, and I haven't tried a 2.0 MHz IF filter, which you
may or may not have done.

I have tried getting 455 kHz IFTs to go wider, but I was dissapointed with
overall results, because I'd have needed 3 IFTs, and lots of damping.

I got 10 kHz of audio BW at low thd using simple methods of damping, sliding IFT1
coils closer,
and some RC boosting of audio HF.
I thus achieved the use of tubes, good AF BW, and excellent local station
selectivity, which allowed me to hear my wanted 300 watt station without
the 5,000 watt station able to be heard even though it is only 45 kHz away.

I at least have cited some concrete facts about
IF filters, while you have only muttered about Q, without indicating how
it actually relates to the problem. I am not a "filter jock" (tm) but I
think it is generally desirable that the Q of the components used in a
filter be high, especially when we get beyond simple double tuned
transformers. What you are calling Q is more related to how the filter is
terminated, which is a different matter than the Q of the components that
make up the filter.

I leave you to wonder the full content of my mutterings,
and I do hope you spend some time soon in your shack with a soldering iron
and response meter.

The other advantage of a 2 MHz IF is that the filtering of RF from the recovered
audio is easier, because the C value is less, and the filter used has less effect
on recovered audio at 10 kHz, and at high amplitudes.

But don't let me mention it, I know you'd be aware of it already.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

There may be
architectural advantages to using one or the other IF frequency in a
radio, but so far only the bandwidth/selectivity has been
mentioned and in
that regard an IF of 2.0 MHz offers no significant advantage over a 455
kHz IF for the reception of the full audio bandwidth.

I supect it might, and one article in Wireless World refered to using
10.7 MHz.

Certainly a high IF frequency will have advantages in image response, but
if the bandwidth is the same, the audio quality should be similar. What
exactly did Wireless World say was so great about using a 10.7 MHz IF for
a MW AM receiver?

Wide AF response was easily achieved.

Wireless World is a hobbyist magazine and all their
authors are not necessarily up to speed, although in the old days they
often did have articles by people who knew what they were talking about
with respect to radios.

I differ. WW and what it became, Electronics World wasn't just an
amateur's magazine. It had cutting edge articles about electronics
from 1917 onwards, and I suggest you park yourself beside a
pile of all the old copies and have a good read.
Most of the info was only comprehensible by very well university educated
professionals, or intellectuals, and most ideas were backed up with
mathematical
proofs which nearly all the general public couldn't understand.

I am reasonably familiar with Wireless World, I have 3 & 1/2 of those copy
paper boxes full of old issues from the 1930's through the 1950's. I
would estimate that I have at least half the issues from that period whcih
was probably the golden age of AM receiver technology. I have to take
serious exception to your characterization of the "mathematical proofs"
included in their articles. There may have been the odd article with some
mathematical depth, but those were few and far between. The math
presented seems to have been just enough to go over the head of the
average reader, but was hardly complex enough to be "only comprehensible
by very well university educated professionals, or intellectuals". I
suspect this light weight approach just slightly above the level of the
man in the street was carefully calculated to impress the average reader
without putting the material at a level where he couldn't understand it at
all. That is not to say that they didn't have many excellent authors who
knew all the math, but it is a serious stretch to imply that they included
any real mathematical depth, they included only enough to look impressive
to the untutored reader.

I suspect that the reason Wireless World might
have used a 10.7 MHz IF in a MW AM broadcast receiver is because it was an
easy way for a hobbyist, who both doesn't have a clue what he is doing,
and doesn't have the necessary test equipment, to get a super wide
bandwidth.

I leave you to your suppositions.


OK, but for all practical purposes my "supposition" seems to be identical
with your statement above that "Wide AF response was easily achieved",
which I take to be a quote from the actual Wireless World article?

Damping reduces Q, and increases BW.
But it also reduces Z at Fo, thus reducing gain in an amp
which must be a current source, like a pentode or j-fet,
to realise the best selectivity for the LC circuit.

This is a half truth, what matters is that the filter is correctly
terminated, not that pentode, triode or whatever drives it. As far as
stage gain goes, increasing the frequency from 455 kHz to 2.0 MHz is
likely to decrease the gain by a similar amount to widening the 455 kHz
filter to the same bandwidth as the 2.0 MHz filter.

What I said was what I said.
You are confused.

Maybe, in what way are you suggesting I am confused? I would suggest to
you that you don't understand how to design an IF filter, and don't
understand what can be done at 455 kHz.

I know enough about IFT design, after having built my own radio.

That isn't clear at all, you seem to be obsessed with "Q", and hardly if
ever mention "k", and how it relates to "Q" in determining the
characteristics of an IFT. You occasionally mention "critical" coupling
but haven't tied that concept in with the "Q" and "k" of an IFT, nor have
you mentioned the related concept of "transitional" coupling. I would
expect to hear more mention of these concepts from someone who knows
"enough about IFT design".


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

There may be
architectural advantages to using one or the other IF frequency in a
radio, but so far only the bandwidth/selectivity has been
mentioned and in
that regard an IF of 2.0 MHz offers no significant advantage over a 455
kHz IF for the reception of the full audio bandwidth.

I supect it might, and one article in Wireless World refered to using
10.7 MHz.

Certainly a high IF frequency will have advantages in image response, but
if the bandwidth is the same, the audio quality should be similar. What
exactly did Wireless World say was so great about using a 10.7 MHz IF for
a MW AM receiver?

Wide AF response was easily achieved.

Wireless World is a hobbyist magazine and all their
authors are not necessarily up to speed, although in the old days they
often did have articles by people who knew what they were talking about
with respect to radios.

I differ. WW and what it became, Electronics World wasn't just an
amateur's magazine. It had cutting edge articles about electronics
from 1917 onwards, and I suggest you park yourself beside a
pile of all the old copies and have a good read.
Most of the info was only comprehensible by very well university educated
professionals, or intellectuals, and most ideas were backed up with
mathematical
proofs which nearly all the general public couldn't understand.

I am reasonably familiar with Wireless World, I have 3 & 1/2 of those copy
paper boxes full of old issues from the 1930's through the 1950's. I
would estimate that I have at least half the issues from that period whcih
was probably the golden age of AM receiver technology. I have to take
serious exception to your characterization of the "mathematical proofs"
included in their articles. There may have been the odd article with some
mathematical depth, but those were few and far between. The math
presented seems to have been just enough to go over the head of the
average reader, but was hardly complex enough to be "only comprehensible
by very well university educated professionals, or intellectuals".

I never learnt any electronics maths at high school.
I was told that if I went into a career as an electronics design engineer,
I'd have to be far better at maths.

I agree, many articles don't have much maths, but a lot do,
and all one can do is read between the lines of incomprehensible maths.
By the mid 1970s, there were many young bright mainly british stars
who showed off their mathematical abilities, most probably to appear
to be stars, and top of the bloomin heap, and to foster good future employment with
major electronics firms.

The readers' letters section daown the back of the mag had the arguments between
engineers who
couldn't agree. Plenty of that alright.

The internet changed all that, along with everyone trying to keep progress secret
as possible,
and only for eyes of the financial backers.


I
suspect this light weight approach just slightly above the level of the
man in the street was carefully calculated to impress the average reader
without putting the material at a level where he couldn't understand it at
all. That is not to say that they didn't have many excellent authors who
knew all the math, but it is a serious stretch to imply that they included
any real mathematical depth, they included only enough to look impressive
to the untutored reader.

Well, there was a pile of stuff I couldn't understand.

I just got the general idea and built stuff, and got very nice results as good
as anyone with all that math ability would.



I suspect that the reason Wireless World might
have used a 10.7 MHz IF in a MW AM broadcast receiver is because it was an
easy way for a hobbyist, who both doesn't have a clue what he is doing,
and doesn't have the necessary test equipment, to get a super wide
bandwidth.

I leave you to your suppositions.

OK, but for all practical purposes my "supposition" seems to be identical
with your statement above that "Wide AF response was easily achieved",
which I take to be a quote from the actual Wireless World article?

Not my quote of WW.
But basically, one of the aims was expressed to mean thy same as I said.



Damping reduces Q, and increases BW.
But it also reduces Z at Fo, thus reducing gain in an amp
which must be a current source, like a pentode or j-fet,
to realise the best selectivity for the LC circuit.

This is a half truth, what matters is that the filter is correctly
terminated, not that pentode, triode or whatever drives it.

Well most IFTs made for tube radios would perform abysmally is driven
with triode amps with Ra = say 10k.
This would over damp the LC circuit in most cases.

Try damping an ordinary radio's IFTs with 100K, then 47k and finally 22k
for each of the 4 IF coils in a set.
Tell me what you find.

As far as
stage gain goes, increasing the frequency from 455 kHz to 2.0 MHz is
likely to decrease the gain by a similar amount to widening the 455 kHz
filter to the same bandwidth as the 2.0 MHz filter.

Use 3 x IFTs, and an extra stage of IF amplification.
I still reckon the 2MHz will work, and when I have time,
I'll try the idea, and tell everyone about it.

But to know any earlier, try it out for yourself.



What I said was what I said.
You are confused.

Maybe, in what way are you suggesting I am confused? I would suggest to
you that you don't understand how to design an IF filter, and don't
understand what can be done at 455 kHz.

I know enough about IFT design, after having built my own radio.

That isn't clear at all, you seem to be obsessed with "Q", and hardly if
ever mention "k", and how it relates to "Q" in determining the
characteristics of an IFT. You occasionally mention "critical" coupling
but haven't tied that concept in with the "Q" and "k" of an IFT, nor have
you mentioned the related concept of "transitional" coupling. I would
expect to hear more mention of these concepts from someone who knows
"enough about IFT design".

I don't need to use k to confuse everyone.

An IFT is a simple RF transformer operating at a fixed F.
The magnetic lines of force from one coil react to transfer
some power from a primary LC to a secondary LC.

The coupling and insertion loss is whatever you are gonna get.
The looser the coupling, ie, the further apart the coils, the
sharper is the nose shape of the two circuits.
Let's assume you have a current source, ie, high impedance
signal source, or generator for the primary.
Assume the output from the sec goes to a high impedance load, like the grid
of a pentode tube, with little miller capacitance.
The load of the sec LC is transfered to the pri, depending on the closeness
of coupling.

Far apart gives a large insertion loss, and lowest RL for the pri signal source,
but the response shows the attenuation
is twice that of a single LC as you move away from the centre F.
Then as you bring the coils together, the insertion loss and load value reduces,
and the
response suddenly becomes flat topped, but the attenuation out of the pass band is
still
twice that of a single circuit.
Then with coils even closer, the insertion loss is low, but there are two peaks in
the response,
but outside the two peaks the response remains twice that of a single LC circuit.

k isn't needed to be considered since we are dealing practically with what you get
when you
use LC circuits arranged as they are in IFTs.
We simply wanna know what happens.
Its also spelled out in numerous old radio books, and there are maths for those
inclined.

The beauty of audio and radio engineering is that a lot of it can be done using
only very basic maths, and following well known practices and precautions.
It isn't as complex as rocket science.
We don't have to worry if we shoot some dude off into space, and find that our
equations were
wrong, and he spends eternity orbitting Mars with no way back.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

Damping reduces Q, and increases BW.
But it also reduces Z at Fo, thus reducing gain in an amp
which must be a current source, like a pentode or j-fet,
to realise the best selectivity for the LC circuit.

This is a half truth, what matters is that the filter is correctly
terminated, not that pentode, triode or whatever drives it.

Well most IFTs made for tube radios would perform abysmally is driven
with triode amps with Ra = say 10k.
This would over damp the LC circuit in most cases.

That is true of "IFTs made for tube radios" when they are being used as
originally intended, but what happens when we hobbyists modify them for
High-Fidelity use by increasing "k" and decreasing the circuit "Q" by
adding resistors? In this case since we need external termination
resistors anyway, all we need do is connect the resistor between the anode
of the triode and the input of the IFT and all will be well, there is no
need for a current source to drive the filter, ideal would be a source
with just the required termination resistance. There is no reason why the
required termination resistance can't be connected between a low impedance
source and the input of the filter, it does not have to have one end
earthed.

Try damping an ordinary radio's IFTs with 100K, then 47k and finally 22k
for each of the 4 IF coils in a set.
Tell me what you find.

Every filter, be it an IFT or something more complex, is designed to be
terminated in specified impedances, which may be a specified resistance,
an open circuit, or even a short circuit, what matters is that the
termination is correct, not that the filter is driven by a pentode.

As far as
stage gain goes, increasing the frequency from 455 kHz to 2.0 MHz is
likely to decrease the gain by a similar amount to widening the 455 kHz
filter to the same bandwidth as the 2.0 MHz filter.

Use 3 x IFTs, and an extra stage of IF amplification.
I still reckon the 2MHz will work, and when I have time,
I'll try the idea, and tell everyone about it.

But to know any earlier, try it out for yourself.

I never said 2.0 MHz wouldn't work, in fact I specifically stated at least
once that I thought 2.0 MHz would work. If 2.0 MHz is what floats your
boat then that's what you should use, although I notice that you choose to
use the traditional 455 kHz in your radio design. What I said was simply
that 455 kHz would also work in a wideband High-Fidelity AM radio.

What I said was what I said.
You are confused.

Maybe, in what way are you suggesting I am confused? I would suggest to
you that you don't understand how to design an IF filter, and don't
understand what can be done at 455 kHz.

I know enough about IFT design, after having built my own radio.

That isn't clear at all, you seem to be obsessed with "Q", and hardly if
ever mention "k", and how it relates to "Q" in determining the
characteristics of an IFT. You occasionally mention "critical" coupling
but haven't tied that concept in with the "Q" and "k" of an IFT, nor have
you mentioned the related concept of "transitional" coupling. I would
expect to hear more mention of these concepts from someone who knows
"enough about IFT design".

I don't need to use k to confuse everyone.

An IFT is a simple RF transformer operating at a fixed F.
The magnetic lines of force from one coil react to transfer
some power from a primary LC to a secondary LC.

The coupling and insertion loss is whatever you are gonna get.
The looser the coupling, ie, the further apart the coils, the
sharper is the nose shape of the two circuits.
Let's assume you have a current source, ie, high impedance
signal source, or generator for the primary.
Assume the output from the sec goes to a high impedance load, like the grid
of a pentode tube, with little miller capacitance.
The load of the sec LC is transfered to the pri, depending on the closeness
of coupling.

Far apart gives a large insertion loss, and lowest RL for the pri signal
source,
but the response shows the attenuation
is twice that of a single LC as you move away from the centre F.
Then as you bring the coils together, the insertion loss and load value
reduces,
and the
response suddenly becomes flat topped, but the attenuation out of the
pass band is
still
twice that of a single circuit.
Then with coils even closer, the insertion loss is low, but there are
two peaks in
the response,
but outside the two peaks the response remains twice that of a single LC
circuit.

k isn't needed to be considered since we are dealing practically with
what you get
when you
use LC circuits arranged as they are in IFTs.
We simply wanna know what happens.

If you simply "wanna know what happens" why do you even need to consider
"Q"? Your narrative description above sure makes it sound like "k" is
important, you just haven't tied "Q" and "k" to the response shapes you
describe.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/