In Patrick Turner's latest message replying to the thread I started on
building a high-performance AM tube tuner, he stated his skepticism
that a pure TRF circuit will, in a practical sense, meet the specs I'm
looking for (to meet the specs will require an impractical number of
RF amplifier stages, such as six or more.)

Within the design constraints he selected, I cannot disagree with his
conclusion.

However, one of the constraints he made, and that most make, is that
tuning is to be done by an infinitely variable multigang air
capacitor.

I wonder if the same conclusion would be reached if we approach this
from a single channel perspective? That is, what if we fix the
frequency we want to receive (e.g., 830khz, or 1420khz), and then for
each stage optimize the parallel RLC circuit (or use some other tuned
circuit with the right resonance and bandwidth response -- crystals?)

With the much greater design freedom this should allow, could we now
possibly meet the specs with only two or three RF amps, for any
frequency in the 500 to 1800khz range? For a simplified diagram of a
two RF stage TRF receiver, see page 7 of:


http://www.technology.niagarac.on.ca...531unit6rx.ppt

Now, if this single channel approach indeed makes TRF more attractive,
then the next step is obvious -- consider building the TRF AM tuner
with selectable channels. Obviously, the downsides to this a the
need for a switch, the complexity and cost of having lots of channels
if we want to cover the whole BCB range (e.g., 120+, every 10khz in
North America, and 9khz in Europe and elsewhere), and the issue of
oscillation due to interference between the RF stages (shielding and
proper layout design will likely be very critical.) I envision the
tuned circuits for each channel being put on a mini-board which will
plug into a slot, but then there may be other ways to handle the large
number of tuned circuits necessary to cover the whole BCB (360+ of
them -- this does sound quite expensive.)

Thoughts?

*****

Of course, the other alternative is to modernize a proven design of a
super-het tube radio from yesteryear (the final audio amplifier will
be stripped out, replaced with a line-out.) Which radio circuits
would you nominate (with improvements), which provide excellent audio
fidelity (probably with variable bandwidth control), very good
sensitivity and selectivity, and other desirable specs? In addition,
the circuit design should be "forgiving", so those who build it from
kits (with pre-made PCB boards and proper guidance on layout and
shielding) will likely be successful -- the parts, too, should be
purchasable as NS from somewhere (NO SCROUNGING for old used parts as
I've noted before). We probably need to make special arrangements for
producing the various coils, since not everyone is going to want to
wind their own coils.


Jon Noring

TRFs are nice receivers, I had several back in the 1950s becasue that's all
I could find for free or next to nothing. The problem with a tuneable TRF
is that the bandwidth increases as you tune to higher frequencies. BW=f/Q
with Q being relatively constant over the BCB. Since you seem to have a
passion for a fix tuned TRF I'd suggest using old IF transformers for your
coils. It should be relatively easy to remove turns to get the freq up.
Some receivers, particularly military ones were made with IFs in the BCB.
The BC-454 that covered 6 to 9 Mcs had an IF of 1415 Kc. The BC-348 has an
IF of 915 Kc and the BC-312 and BC-342 also skipped the BCB but I can't
recall their IFs but I'll bet Google will find em. Scour the hamfests and
you'll find plenty but prices are going up. If you can find a BC-946 you'll
have a gem for a BCB Rx.
--
73
Hank WD5JFR

"Jon Noring" wrote in message
...
In Patrick Turner's latest message replying to the thread I started on
building a high-performance AM tube tuner, he stated his skepticism
that a pure TRF circuit will, in a practical sense, meet the specs I'm
looking for (to meet the specs will require an impractical number of
RF amplifier stages, such as six or more.)

Within the design constraints he selected, I cannot disagree with his
conclusion.

However, one of the constraints he made, and that most make, is that
tuning is to be done by an infinitely variable multigang air
capacitor.

I wonder if the same conclusion would be reached if we approach this
from a single channel perspective? That is, what if we fix the
frequency we want to receive (e.g., 830khz, or 1420khz), and then for
each stage optimize the parallel RLC circuit (or use some other tuned
circuit with the right resonance and bandwidth response -- crystals?)

With the much greater design freedom this should allow, could we now
possibly meet the specs with only two or three RF amps, for any
frequency in the 500 to 1800khz range? For a simplified diagram of a
two RF stage TRF receiver, see page 7 of:


http://www.technology.niagarac.on.ca...531unit6rx.ppt

Now, if this single channel approach indeed makes TRF more attractive,
then the next step is obvious -- consider building the TRF AM tuner
with selectable channels. Obviously, the downsides to this a the
need for a switch, the complexity and cost of having lots of channels
if we want to cover the whole BCB range (e.g., 120+, every 10khz in
North America, and 9khz in Europe and elsewhere), and the issue of
oscillation due to interference between the RF stages (shielding and
proper layout design will likely be very critical.) I envision the
tuned circuits for each channel being put on a mini-board which will
plug into a slot, but then there may be other ways to handle the large
number of tuned circuits necessary to cover the whole BCB (360+ of
them -- this does sound quite expensive.)

Thoughts?

*****

Of course, the other alternative is to modernize a proven design of a
super-het tube radio from yesteryear (the final audio amplifier will
be stripped out, replaced with a line-out.) Which radio circuits
would you nominate (with improvements), which provide excellent audio
fidelity (probably with variable bandwidth control), very good
sensitivity and selectivity, and other desirable specs? In addition,
the circuit design should be "forgiving", so those who build it from
kits (with pre-made PCB boards and proper guidance on layout and
shielding) will likely be successful -- the parts, too, should be
purchasable as NS from somewhere (NO SCROUNGING for old used parts as
I've noted before). We probably need to make special arrangements for
producing the various coils, since not everyone is going to want to
wind their own coils.


Jon Noring

BC 312/342 IF (at least mine) is 470KC.

The 3-6 MC ARC 5 receiver IF is 1415, the 6-9.1 range ARC 5 radio IF
is 2830.


Nice thing about these ARC 5 sets is often the transformers have been
fully enclosed for 60 years and are still shuny and new looking. A beat
up 6-9.1 range one wouldn't be too hard to turn up (I've got one here
somewhere if anyone seriously wants to give this notion a shot).
High IF's do sound good. The Philco 42-350 (IIRC) uses the same ~5MC
IF for all the bands. Quite a bit less gain per stage than 455KC will
deliver, but closer to simple receiver quality audio.

Jeff Goldsmith





Henry Kolesnik wrote:

TRFs are nice receivers, I had several back in the 1950s becasue that's all
I could find for free or next to nothing. The problem with a tuneable TRF
is that the bandwidth increases as you tune to higher frequencies. BW=f/Q
with Q being relatively constant over the BCB. Since you seem to have a
passion for a fix tuned TRF I'd suggest using old IF transformers for your
coils. It should be relatively easy to remove turns to get the freq up.
Some receivers, particularly military ones were made with IFs in the BCB.
The BC-454 that covered 6 to 9 Mcs had an IF of 1415 Kc. The BC-348 has an
IF of 915 Kc and the BC-312 and BC-342 also skipped the BCB but I can't
recall their IFs but I'll bet Google will find em. Scour the hamfests and
you'll find plenty but prices are going up. If you can find a BC-946 you'll
have a gem for a BCB Rx.
--
73
Hank WD5JFR

"Jon Noring" wrote in message
...
In Patrick Turner's latest message replying to the thread I started on
building a high-performance AM tube tuner, he stated his skepticism
that a pure TRF circuit will, in a practical sense, meet the specs I'm
looking for (to meet the specs will require an impractical number of
RF amplifier stages, such as six or more.)

Within the design constraints he selected, I cannot disagree with his
conclusion.

However, one of the constraints he made, and that most make, is that
tuning is to be done by an infinitely variable multigang air
capacitor.

I wonder if the same conclusion would be reached if we approach this
from a single channel perspective? That is, what if we fix the
frequency we want to receive (e.g., 830khz, or 1420khz), and then for
each stage optimize the parallel RLC circuit (or use some other tuned
circuit with the right resonance and bandwidth response -- crystals?)

With the much greater design freedom this should allow, could we now
possibly meet the specs with only two or three RF amps, for any
frequency in the 500 to 1800khz range? For a simplified diagram of a
two RF stage TRF receiver, see page 7 of:


http://www.technology.niagarac.on.ca...531unit6rx.ppt

Now, if this single channel approach indeed makes TRF more attractive,
then the next step is obvious -- consider building the TRF AM tuner
with selectable channels. Obviously, the downsides to this a the
need for a switch, the complexity and cost of having lots of channels
if we want to cover the whole BCB range (e.g., 120+, every 10khz in
North America, and 9khz in Europe and elsewhere), and the issue of
oscillation due to interference between the RF stages (shielding and
proper layout design will likely be very critical.) I envision the
tuned circuits for each channel being put on a mini-board which will
plug into a slot, but then there may be other ways to handle the large
number of tuned circuits necessary to cover the whole BCB (360+ of
them -- this does sound quite expensive.)

Thoughts?

*****

Of course, the other alternative is to modernize a proven design of a
super-het tube radio from yesteryear (the final audio amplifier will
be stripped out, replaced with a line-out.) Which radio circuits
would you nominate (with improvements), which provide excellent audio
fidelity (probably with variable bandwidth control), very good
sensitivity and selectivity, and other desirable specs? In addition,
the circuit design should be "forgiving", so those who build it from
kits (with pre-made PCB boards and proper guidance on layout and
shielding) will likely be successful -- the parts, too, should be
purchasable as NS from somewhere (NO SCROUNGING for old used parts as
I've noted before). We probably need to make special arrangements for
producing the various coils, since not everyone is going to want to
wind their own coils.


Jon Noring

"Henry Kolesnik" wrote in message
m...
TRFs are nice receivers, I had several back in the 1950s becasue that's
all
I could find for free or next to nothing. The problem with a tuneable TRF
is that the bandwidth increases as you tune to higher frequencies. BW=f/Q
with Q being relatively constant over the BCB. Since you seem to have a
passion for a fix tuned TRF I'd suggest using old IF transformers for your
coils. It should be relatively easy to remove turns to get the freq up.
Some receivers, particularly military ones were made with IFs in the BCB.
The BC-454 that covered 6 to 9 Mcs had an IF of 1415 Kc. ******
The BC-348 has an IF of 915 Kc and the BC-312 and BC-342 also
skipped the BCB but I can't recall their IFs but I'll bet Google will find
em.
Scour the hamfests and you'll find plenty but prices are going up.
If you can find a BC-946 you'll
have a gem for a BCB Rx.

*******
Sorry to disagree but:
R27/ARC5 - BC 455 (6-9 megs) IF = 2.830 megs
R26/ARC5 - BC454 (3-6 megs) IF = 1.415 megs
R23/ARC5 - BC453 (0.19 - 0.5 megs) IF = 0.085 megs (85 kcs.)
R25/ARC5 (1.5 - 3.0 megs) IF = 0.705 megs (705 kcs)
R24/ARC5 (0.52 - 1500 megs) IF = 0.239 megs (239 kcs)
This from info that J. Gibson was most kind to send me.
Terry

Jeff Goldsmith wrote:

BC 312/342 IF (at least mine) is 470KC.

The 3-6 MC ARC 5 receiver IF is 1415, the 6-9.1 range ARC 5 radio IF
is 2830.

Nice thing about these ARC 5 sets is often the transformers have been
fully enclosed for 60 years and are still shuny and new looking. A beat
up 6-9.1 range one wouldn't be too hard to turn up (I've got one here
somewhere if anyone seriously wants to give this notion a shot).
High IF's do sound good. The Philco 42-350 (IIRC) uses the same ~5MC
IF for all the bands. Quite a bit less gain per stage than 455KC will
deliver, but closer to simple receiver quality audio.

5MHz is high, and many old TVs have 4.5 MHz IFTs within that could be altered.

The final Q of a normal 455 kHz 2 stage IF system is usually 65.
If the final Q of the 5 MHz IF system was also 65, the pass band would be 77 kHz,

allowing stations only 45 kHz apart on the BCB to be all too plainly heard,
although the audio response could be out to 38 kHz.

That's why I proposed an IF just above the BCB at 2 MHz,
where an overall Q of 65 would give a pass band of 31 kHz,
with some hope of attenuating stations only 45 kHz away from the wanted station.
Audio BW could be up to 15.5 kHz.
So a slightly higher overall Q would be permissable.
There is still need for 6 consecutive tuned circuits to give a steep
skirt slope just away from resonance peaks.
It may be possible to have all single tuned LC circuits, each with a Q
of say 40, or a pass band of 50 kHz, so that after 6 circuits this has been
reduced to
20 kHz or therabouts.

But then each single tuned circuit has to be coupled in pairs, which
involves an insertion loss, and pairer critically coupled IFTs and active but low
gain
stages are required.

Patrick Turner.







Jeff Goldsmith

Henry Kolesnik wrote:

TRFs are nice receivers, I had several back in the 1950s becasue that's all
I could find for free or next to nothing. The problem with a tuneable TRF
is that the bandwidth increases as you tune to higher frequencies. BW=f/Q
with Q being relatively constant over the BCB. Since you seem to have a
passion for a fix tuned TRF I'd suggest using old IF transformers for your
coils. It should be relatively easy to remove turns to get the freq up.
Some receivers, particularly military ones were made with IFs in the BCB.
The BC-454 that covered 6 to 9 Mcs had an IF of 1415 Kc. The BC-348 has an
IF of 915 Kc and the BC-312 and BC-342 also skipped the BCB but I can't
recall their IFs but I'll bet Google will find em. Scour the hamfests and
you'll find plenty but prices are going up. If you can find a BC-946 you'll
have a gem for a BCB Rx.
--
73
Hank WD5JFR

"Jon Noring" wrote in message
...
In Patrick Turner's latest message replying to the thread I started on
building a high-performance AM tube tuner, he stated his skepticism
that a pure TRF circuit will, in a practical sense, meet the specs I'm
looking for (to meet the specs will require an impractical number of
RF amplifier stages, such as six or more.)

Within the design constraints he selected, I cannot disagree with his
conclusion.

However, one of the constraints he made, and that most make, is that
tuning is to be done by an infinitely variable multigang air
capacitor.

I wonder if the same conclusion would be reached if we approach this
from a single channel perspective? That is, what if we fix the
frequency we want to receive (e.g., 830khz, or 1420khz), and then for
each stage optimize the parallel RLC circuit (or use some other tuned
circuit with the right resonance and bandwidth response -- crystals?)

With the much greater design freedom this should allow, could we now
possibly meet the specs with only two or three RF amps, for any
frequency in the 500 to 1800khz range? For a simplified diagram of a
two RF stage TRF receiver, see page 7 of:


http://www.technology.niagarac.on.ca...531unit6rx.ppt

Now, if this single channel approach indeed makes TRF more attractive,
then the next step is obvious -- consider building the TRF AM tuner
with selectable channels. Obviously, the downsides to this a the
need for a switch, the complexity and cost of having lots of channels
if we want to cover the whole BCB range (e.g., 120+, every 10khz in
North America, and 9khz in Europe and elsewhere), and the issue of
oscillation due to interference between the RF stages (shielding and
proper layout design will likely be very critical.) I envision the
tuned circuits for each channel being put on a mini-board which will
plug into a slot, but then there may be other ways to handle the large
number of tuned circuits necessary to cover the whole BCB (360+ of
them -- this does sound quite expensive.)

Thoughts?

*****

Of course, the other alternative is to modernize a proven design of a
super-het tube radio from yesteryear (the final audio amplifier will
be stripped out, replaced with a line-out.) Which radio circuits
would you nominate (with improvements), which provide excellent audio
fidelity (probably with variable bandwidth control), very good
sensitivity and selectivity, and other desirable specs? In addition,
the circuit design should be "forgiving", so those who build it from
kits (with pre-made PCB boards and proper guidance on layout and
shielding) will likely be successful -- the parts, too, should be
purchasable as NS from somewhere (NO SCROUNGING for old used parts as
I've noted before). We probably need to make special arrangements for
producing the various coils, since not everyone is going to want to
wind their own coils.


Jon Noring

Jon Noring wrote in message . ..
In Patrick Turner's latest message replying to the thread I started on
building a high-performance AM tube tuner, he stated his skepticism
that a pure TRF circuit will, in a practical sense, meet the specs I'm
looking for (to meet the specs will require an impractical number of
RF amplifier stages, such as six or more.)

Within the design constraints he selected, I cannot disagree with his
conclusion.

However, one of the constraints he made, and that most make, is that
tuning is to be done by an infinitely variable multigang air
capacitor.

I wonder if the same conclusion would be reached if we approach this
from a single channel perspective? That is, what if we fix the
frequency we want to receive (e.g., 830khz, or 1420khz), and then for
each stage optimize the parallel RLC circuit (or use some other tuned
circuit with the right resonance and bandwidth response -- crystals?)

BUt you need to realize that receiver design is about looking at
the overall picture, not some fine point here or there.

There are tradeoffs when using a superheterodyne, but not using
it has to be the rare exception. The tradeoffs have nothing to
do with issues of selectivity.

You have somehow become fixated on TRF receivers, as if it is
the grail to solve some problem that you haven't really defined
yet.

But once you start building good filters, then what's the point of
not using a superhet, and putting that filter at a fixed frequency,
where selectivity will be constant? You're not going to get
"higher fidelity" by moving the filter to the front end. You haven't
come up with reasons why a superhet is not suitable. You're not
really talking "high performance" as many people would think of it,
you are talking "high fidelity". For that purpose, and until you
come up with reasons of image rejection or front end overload, you
won't even notice that you are using a superhet rather than a TRF.

The issue isn't where the filter lies, the issue is getting your
"high performance filter". Realistically, that can be accomplished
far more easily at a fixed IF than by putting it at the front end.
What you need to be concerned about is proper care in designing
that filter. Design it for wide bandwidth but with good skirt
selectivity, and that's all that matters to your end game.

Michael

(Michael Black) wrote in message . com...
Jon Noring wrote in message . ..
In Patrick Turner's latest message replying to the thread I started on
building a high-performance AM tube tuner, he stated his skepticism
that a pure TRF circuit will, in a practical sense, meet the specs I'm
looking for (to meet the specs will require an impractical number of
RF amplifier stages, such as six or more.)

Within the design constraints he selected, I cannot disagree with his
conclusion.

However, one of the constraints he made, and that most make, is that
tuning is to be done by an infinitely variable multigang air
capacitor.

I wonder if the same conclusion would be reached if we approach this
from a single channel perspective? That is, what if we fix the
frequency we want to receive (e.g., 830khz, or 1420khz), and then for
each stage optimize the parallel RLC circuit (or use some other tuned
circuit with the right resonance and bandwidth response -- crystals?)

BUt you need to realize that receiver design is about looking at
the overall picture, not some fine point here or there.

There are tradeoffs when using a superheterodyne, but not using
it has to be the rare exception. The tradeoffs have nothing to
do with issues of selectivity.

You have somehow become fixated on TRF receivers, as if it is
the grail to solve some problem that you haven't really defined
yet.

But once you start building good filters, then what's the point of
not using a superhet, and putting that filter at a fixed frequency,
where selectivity will be constant? You're not going to get
"higher fidelity" by moving the filter to the front end. You haven't
come up with reasons why a superhet is not suitable. You're not
really talking "high performance" as many people would think of it,
you are talking "high fidelity". For that purpose, and until you
come up with reasons of image rejection or front end overload, you
won't even notice that you are using a superhet rather than a TRF.

The issue isn't where the filter lies, the issue is getting your
"high performance filter". Realistically, that can be accomplished
far more easily at a fixed IF than by putting it at the front end.
What you need to be concerned about is proper care in designing
that filter. Design it for wide bandwidth but with good skirt
selectivity, and that's all that matters to your end game.

Michael

See your radio for details. Price and participation may vary. RF--I'm lovin' it.

Michael
Amen brother but you have to give Jon credit for his pursuit as he will
learn much and he'll be able to tell us why Marantz or McIntosh didn't make
a High Quality TRF tuner. Or maybe we'll all be drooling over the Noring
High Quality TRF tuner. Or maybe he'll morf from Noring to Notrf!
--
73
Hank WD5JFR

"Michael Black" wrote in message
om...
Jon Noring wrote in message
. ..
In Patrick Turner's latest message replying to the thread I started on
building a high-performance AM tube tuner, he stated his skepticism
that a pure TRF circuit will, in a practical sense, meet the specs I'm
looking for (to meet the specs will require an impractical number of
RF amplifier stages, such as six or more.)

Within the design constraints he selected, I cannot disagree with his
conclusion.

However, one of the constraints he made, and that most make, is that
tuning is to be done by an infinitely variable multigang air
capacitor.

I wonder if the same conclusion would be reached if we approach this
from a single channel perspective? That is, what if we fix the
frequency we want to receive (e.g., 830khz, or 1420khz), and then for
each stage optimize the parallel RLC circuit (or use some other tuned
circuit with the right resonance and bandwidth response -- crystals?)

BUt you need to realize that receiver design is about looking at
the overall picture, not some fine point here or there.

There are tradeoffs when using a superheterodyne, but not using
it has to be the rare exception. The tradeoffs have nothing to
do with issues of selectivity.

You have somehow become fixated on TRF receivers, as if it is
the grail to solve some problem that you haven't really defined
yet.

But once you start building good filters, then what's the point of
not using a superhet, and putting that filter at a fixed frequency,
where selectivity will be constant? You're not going to get
"higher fidelity" by moving the filter to the front end. You haven't
come up with reasons why a superhet is not suitable. You're not
really talking "high performance" as many people would think of it,
you are talking "high fidelity". For that purpose, and until you
come up with reasons of image rejection or front end overload, you
won't even notice that you are using a superhet rather than a TRF.

The issue isn't where the filter lies, the issue is getting your
"high performance filter". Realistically, that can be accomplished
far more easily at a fixed IF than by putting it at the front end.
What you need to be concerned about is proper care in designing
that filter. Design it for wide bandwidth but with good skirt
selectivity, and that's all that matters to your end game.

Michael

"Henry Kolesnik" wrote in message om...
Michael
Amen brother but you have to give Jon credit for his pursuit as he will
learn much and he'll be able to tell us why Marantz or McIntosh didn't make
a High Quality TRF tuner. Or maybe we'll all be drooling over the Noring
High Quality TRF tuner. Or maybe he'll morf from Noring to Notrf!
--
73
Hank WD5JFR

"Michael Black" wrote in message
om...
Jon Noring wrote in message
. ..
In Patrick Turner's latest message replying to the thread I started on
building a high-performance AM tube tuner, he stated his skepticism
that a pure TRF circuit will, in a practical sense, meet the specs I'm
looking for (to meet the specs will require an impractical number of
RF amplifier stages, such as six or more.)

.................................................. .......................

I recall reading about a trf radio that was used in German submarines
in WWII
I think it was in an old QST or 73 about 15 years ago. It was
sensitive and
well shielded and of incredible quality. Perhaps one is available on
the surplus market, or at least the schematic. As I recall, it had a
four-gang tuning condenser. It was a trf design to eliminate any
oscillator radiation that could be picked up by sub-hunters. The trf
radio was in an article describing German radios of WWII.

In article ,
(ken) wrote:

I recall reading about a trf radio that was used in German submarines
in WWII
I think it was in an old QST or 73 about 15 years ago. It was
sensitive and
well shielded and of incredible quality. Perhaps one is available on
the surplus market, or at least the schematic. As I recall, it had a
four-gang tuning condenser.

Only a four-gang tuning condenser, that's not good enough, the W.E. No.
10A has a six-gang tuning condenser, as someone once said you can never
have too many gangs.


REgards,

John Byrns


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