John Byrns wrote:

In article , Patrick Turner
wrote:

I don't have the time to debate this any longer.

Hi Patrick,

You seem to be the one that wants a debate where one is not necessary, or
asked for. There is nothing to debate here, I understand yours and Phil's
position in a qualitative sense, but I find yours and Phil's approach
somewhat counter intuitive, just as you find my approach counter
intuitive. You say that your approach to LC tuned circuits is described
in many text books, I have not found any, although admittedly I have not
been searching specifically for information on your approach to LC tuned
circuits. All I have asked you for is a simple citation to a textbook
where I can find out more about your approach, especially the quantitative
aspects of your approach, and how to make use of it in design problems.
While it is easy to understand your idea from a qualitative perspective, I
don't understand how to actually apply it. I would prefer to learn that
from a textbook rather than taking your time to have you explain it
further.

I don't want to repeat what I have already said.

I'm not asking you to repeat anything, I am only asking you to provide a
citation for one of the textbooks that gives a good description of your
approach to LC tuned circuit design, you have not done that before. Your
continued unwillingness to provide a reference to one of the many
textbooks that you have said describe your perspective on LC tuned circuit
design, while continuing to make the claim, has made it pretty obvious
that your claims relative to textbook explanations is nothing but BS.
That is not to say that your observations are BS, I unraveled that back in
January, it is just the claim that your method may be found in textbooks
that smacks of BS.

I suggest yet again you satisfy your curiosity to inform yourself of the
wonderments we see with LC tuned circuits by reading whatever books exist
on the subjects, and I am sure there is a pile of material on the web.

Yes, I have several books on my bookshelf that explain the "wonderments we
see with LC tuned circuits", that is not a problem, but they explain
methods that are quite different from yours, I am simply looking for a
reference that will more fully explain your methods than what I have been
able to figure out on my own, especially from a quantitative perspective.

Sadly the answer to my question has become crystal clear.

Regards,

John Byrns

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

I hope I don't bore you with long winded repetitions
of what is contained in RDH4 and all the other reputable text books.
But whatever they say, I agree with, so I am not needed for citations and page
numbers.
Go find out for yourself like I did, and be confident.

But to make an ideal AM tuner for local BCB to get at least 9 kHz of bw at low
thd and noise,
the most critical part of the exercize is to make the response of the IF
channel using two IFTs
to give around 8 kHz of bw of audio.

This means 16 kHz of IF bw.

To acheive that, its easier to utilise a pair of existing conventional
IFTs rather than wind one's own which necessitates the use of litz wire,
and special patterned widing techniques.

The IFTs chosen don't need to be a matched pair, but I prefer the types from
1950's radios with larger cans and simple solenoid windings with inductive
tuning.

A preliminary investigation should be made to ascertain the response
at 455 kHz by means of ideally placing the IFT as is into an existing IF amp,
with the detector with two CF as I have posted already established,
The input to the IF amp can be to the IFamp tube grid with about the normal
working bais level.
Only a small input signal is needed, to get about 20vrms of carrier signal at
the anode of the IFT tube
This can easily be measured using a simple peak reading volt meter using
a shielded low input capacitance probe, where you have a 500 pF cap
feeding an SS diode with its anode grounded, and the rectified peak +DV level
generated by the
simple detector is then divided by a 2.2M and 270k divider to approximately
give a 10 : 1 reduction of the DV level.
A schematic for such a simple detector is similar to the AGC diode detector in
the schemo I posted.
Many of the ARRL books carry such a simple RF detector schematic for
immediately
converting RF voltages into a DV which is so much more easily measured
remotely without losses or affecting signal level being measured in the high
impedance circuits concerned.
The peak DV can be read by a DVM across the 270k, and x 10 for the real value.
Its a primitive way to measure the anode RF level, but good enough for what we
want.
With such an RF voltage measurer, we can check the input and output levels of
the IFT,
to make sure the tube is not overloaded, and the insertion losses of the IFT
are not excessive.


The frequency adjustable test signal should be set at exactly 455 kHz, measured
with a ditital F meter,
and the carrier level adjusted for about 28 pk volts read from our network.
With the AGC voltage application shunted at the 0.05 uF first cap in the AGC
line

The IFT is tuned up to give the highest AGC voltage at the detector.

I have a modulated test carrier, so I use a low F of modulation of 100 Hz,
and 30% AM is sufficient.

A page is ruled up in an exercize book to record the response for 50 kHz each
side of 455 kHz,
with one line down the page representing -3 dB.
A CRO is used to monitor the level of recovered audio from the detector,
and perhaps you will have about 2vrms of audio to measure.

The 100 Hz sine wave is displayed on the CRO so it occupies the full height of
the screen.

Then you adjust the F of the sig gene and plot the -3,-6,-12,-18,-24 dB audio
levels and record the
carrier F at which these audio levels occur.
One does the graph for each side of the 455 kHz centre F.

The dots are joined, and the graph can be drawn of the IFT selectivity shape.

The 100 Hz audio will decline very nearly exactly with the decline in RF
response of the IFT,
because the 100 Hz modulation causes sideband frquencies only 100 Hz each side
of 455 kHz.

With an average garden variety IFT that an average radio maker of 1950 may have
made,
you will get -3 dB points at around 3 kHz each side of the 45 kHz, with steep
sides beyond this, then
some flattening out beyond the -12 dB points.
The -3 dB points are known as the F1 and F2 response poles, and F2 - F1 = the
bandwidth.
The overall response should look like a section through a bell,
and there should be an attenuation of -24 dB at about 50 kHz away from 455 kHz.

The aim is to make the IFT response wider, so the transformer is removed from
the chassis,
and the windings removed from the cans, and the tube on which the IF coils are
wound has a 5mm wide
peice of tube former cut out without wrecking the litz wire, cap leads, or
anything else.
Each of the 7 strands of fine wire in the litz wire must remain intact.

A plastic or carboard tube is found to tightly fit over the tube stubs of IF
coils, and the the coils moved closer together,
and reassembled into the can, and back onot the chassis.
The response measurement is repeated, and we should see a wider bandwidth
response,
but the slopes of the attenuation beyond the -3 dB will remain the same.
The reponse may even show a twin, but quite unevely peaked response, and that
because when the
IFTs are peaked up with coils closer the mistake was to tune the IFT so one
coil is centred on 455 kHz,
and the other centred on the side peak F which may be at 458 or 452 kHz, so a
if there are two peaks noticable when peaking up the IFT while aligning it, the
response peaks must be
symetrical each side of the 455 kHz, which might appear in the centre of a
trough
in the response.

Its all quite fiddly, and the novice will get trapped everytime.

The IF coil distance is repeatedly adjusted for a slightly troughed response
with two peaks,
and the bw should then be around 12 kHz.

Then we add some damping resistance of say 150 k to each of the LC windings.

This will usually reduce the sightly twin peaked reposne to a single one,
but which has a broad response of 10 kHz.

Sometimes 100 k dmaping R should be added, but the general idea is to
close the distance between IF coils, and use the least R dampers to produce the
widest
single peaked bandwidth with a nicely symetrical shape, which indicates each LC
is exactly
tuned to 455 kHz.

We repeast the whole process again with the second IFT.

The IFTs can then have their coils carefully glued so their distance cannot
vary, and finally
reassembled and mounted in the set with the mixer tube added.

With the RF input tuning gang tuned to the lowest possible RF frequency,
the IF gene signal can be reduced, and fed into the RF input, and enough 455
kHz will
get through to the mixer anode to test the IF response again,
only this time we can have the AGC allowed to be operational, lest we overload
the
mixer and IF amp with too much signal.

The IFs should be realigned for the highest AGC negative voltage, and
symetrical
response shape, which now should show the -3 dB points at say 7 kHz each side
of 455 kHz,
and at least twice the rates of attenuation recorded with one IFT.

The input test F should then be changed to an RF input signal of say 550 kHz,
and the set tuned to this F for maximum AGC, and quick check of the IF
frequency should reveal
455 kHz, if not, the set slightly tuned so that is the case.
The tuning gang should nearly be fully closed.
If not, the oscilator coil slug is adjusted to where 500 kHz should be.
The set should tune up to the high end of the band, so that RF of 1,650 kHz can
be tuned,
if not, the oscilator gang trim cap adjusted to allow 1,650 kHz.
With the set tuned to 550 kHz, the RF input coil slug should be adjusted for
max AGC,
which shows the RF LC is now tuned to the low RF while producing 455 kHz IF.
The set is then tuned to around 1,400 kHz, and the trim cap on the RF tuning
gang adjusted for
max AGC.
This indicates the RF input is tuned to the high RF whilst producing 455
kHz.IF.

With a constant level of RF input, the AGC level across tha band should vary
by not more than +/- 3 dB.
Sometimes its best to align the best tracking at 650 kHz and 1,300 kHz,
if the wanted stations are all in this bandwidth.

Notice how we have not simulated or calculated a single thing during
this whole tedious process, which should take the unititiated a couple of days
to get right,
using the right type of gear, and making only a few mistakes which are
discovered
along the way by those with a skeptical distrust of their abilities, and an
attitude that they
must proove beyond any doubt that everything they measure all adds up to the
design aim.

The same tedious methods for alignment exist in the text books I have
described.

Little attention in the text books has been given to achieving a pass band as
wide as
8 kHz at least, because the textbooks were often written for the mass market
makers
by manufacturers of tubes, who wanted to make it easy to use their products
with as much ease as possible.
The books give little account of using an audio step filter to slightly
emphasize the
recovered HF audio so that we can boost the initial audio roll off caused by
the
IF response so that the response is stretched a bit further from 7 kHz to 9
kHz.
Trying for more than this is high impossible because an RC compensation network

can only have a slight boost, before the roll off due to the IF shape causes a
massive
roll off rate which is impossible to compensate with any RC network.
And we don't want to over compensate, and end up with a hump in the audio
response
at say 2 kHz.

I am sure anything I left out can be found in the books, so don't bother being
lazy
and asking me questions they can answer.

Patrick Turner.