Last night I posted a couple messages regarding the proposed "channel
TRF" AM tube tuner, focusing on the plug-in mini-board idea as one way
among several possibilities to implement it.

The idea underlying the channel TRF concept is to build bandpass
tuning circuitry specific to, and optimized for, each frequency in the
BCB, instead of fixing that circuitry to some "average" value and
trying to vary it using a traditional variable air capacitor (or
variable inductor) for continuous tuning. A switch would be used to
select the bandpass circuitry for the particular frequency channel the
listener wants to hear.

This would allow, in principle if not in practice, the ability to
very precisely optimize the bandpass circuitry (to maintain a quite
constant bandwidth and shape) for every broadcast frequency in the BCB
(from 500 khz to 1800 khz.)

The "mini-board" variation of the concept would place the bandpass
circuitry for each channel (frequency) onto a small plug-in PCB board.
Depending upon the type and order of bandpass filter used, the number
of components on the mini-board may be quite small, maybe a couple
capacitors, a resistor or two, an inductor, etc., having the optimal
values, and with one or more trimmers for fine adjustment of the
center frequency.

Clearly there are several implementations of the general concept, one
of which is a well-known hybrid that allows continuous tuning in the
more traditional and familiar way. The ones I think of at the moment
a

1) Traditional continuous tuning: Divide the wide BCB into several
sub-bands, such as 5 or even more, each sub-band having optimized
bandpass circuitry for the sub-band, and then use the traditional
variable capacitor or inductor to tune within the narrow sub-band.
Although each channel will no longer have the most optimal bandpass
configuration, it will be closer to optimal.

2) Single Board, True Channel: It may be possible, instead of having
120+ totally independent channel circuits each placed on a separate
mini-board, to put them all onto one larger board, but still keep
all circuits otherwise separate on the board. A lot of components,
and probably a lot of trimmers.

3) Single Board, Shared Components: As a combination of items (1) and
(2), channels which are adjacent to each other (in their own
"sub-band") could probably share a lot of common bandpass
components, thereby reducing the number needed on the board. Only
the large number of trimmers for individual channel calibration
will remain.

The original idea of mini-boards is most advantageous when the user
of the TRF tube tuner only plans to listen to 10-20 stations (such
as local, higher-power stations). They only install the channel
mini-boards they want to listen to.


*****

I do have a couple questions of both John and Patrick (and anyone else
caring to chime in) related to this.

1) In the single frequency TRF tube receiver (a TRF designed strictly
to listen to a single frequency), is there a need for double tuned
circuits? Or will singly tuned circuits be sufficient for
excellent performance (audio quality, sensitivity and
selectivity)? If not, how do double tuned circuits benefit the
overall performance of the single frequency TRF receiver?

2) Let's assume that we decide to design a Mark I TRF AM tube tuner
kit designed solely for more local, higher power stations (thus the
sensitivity is less critical than a tuner to also be used for
casual DXing.) How will this further simplify the optimal single
frequency TRF receiver design? Will only one RF amp stage be
necessary, or will we still need two? The focus now will be on very
high-quality audio reproduction of local stations, which I believe
tubeophiles will be most interested in.


Thanks.

Jon Noring

How many stages you need depends on the selectivity you need because of your
geographic location and antenna Two stations close in frequency will
interfere with each other unless you have enough selectivity. A weak local
station that is strong enough to be heard may get splatter from a distance
station close in frequency that has 50KW or more and a pattern that
concentrates on your area! High Q, double tuning, addtional stages all add
to selectivity. The spuerhet solved this problem.

But if you want to satisfy your demons with a mdoular approach you might
want to consider salvaging a couple of turret type tuners from 1950s TVs.
These have clip in moddules with silver contacts and appropriate LC for each
channel. With todays ferrites you should be able to squeeze-in a LC for AM
BCB. Each tuner will give you 12 channels.

--
73
Hank WD5JFR

"Jon Noring" wrote in message
...
Last night I posted a couple messages regarding the proposed "channel
TRF" AM tube tuner, focusing on the plug-in mini-board idea as one way
among several possibilities to implement it.

The idea underlying the channel TRF concept is to build bandpass
tuning circuitry specific to, and optimized for, each frequency in the
BCB, instead of fixing that circuitry to some "average" value and
trying to vary it using a traditional variable air capacitor (or
variable inductor) for continuous tuning. A switch would be used to
select the bandpass circuitry for the particular frequency channel the
listener wants to hear.

This would allow, in principle if not in practice, the ability to
very precisely optimize the bandpass circuitry (to maintain a quite
constant bandwidth and shape) for every broadcast frequency in the BCB
(from 500 khz to 1800 khz.)

The "mini-board" variation of the concept would place the bandpass
circuitry for each channel (frequency) onto a small plug-in PCB board.
Depending upon the type and order of bandpass filter used, the number
of components on the mini-board may be quite small, maybe a couple
capacitors, a resistor or two, an inductor, etc., having the optimal
values, and with one or more trimmers for fine adjustment of the
center frequency.

Clearly there are several implementations of the general concept, one
of which is a well-known hybrid that allows continuous tuning in the
more traditional and familiar way. The ones I think of at the moment
a

1) Traditional continuous tuning: Divide the wide BCB into several
sub-bands, such as 5 or even more, each sub-band having optimized
bandpass circuitry for the sub-band, and then use the traditional
variable capacitor or inductor to tune within the narrow sub-band.
Although each channel will no longer have the most optimal bandpass
configuration, it will be closer to optimal.

2) Single Board, True Channel: It may be possible, instead of having
120+ totally independent channel circuits each placed on a separate
mini-board, to put them all onto one larger board, but still keep
all circuits otherwise separate on the board. A lot of components,
and probably a lot of trimmers.

3) Single Board, Shared Components: As a combination of items (1) and
(2), channels which are adjacent to each other (in their own
"sub-band") could probably share a lot of common bandpass
components, thereby reducing the number needed on the board. Only
the large number of trimmers for individual channel calibration
will remain.

The original idea of mini-boards is most advantageous when the user
of the TRF tube tuner only plans to listen to 10-20 stations (such
as local, higher-power stations). They only install the channel
mini-boards they want to listen to.


*****

I do have a couple questions of both John and Patrick (and anyone else
caring to chime in) related to this.

1) In the single frequency TRF tube receiver (a TRF designed strictly
to listen to a single frequency), is there a need for double tuned
circuits? Or will singly tuned circuits be sufficient for
excellent performance (audio quality, sensitivity and
selectivity)? If not, how do double tuned circuits benefit the
overall performance of the single frequency TRF receiver?

2) Let's assume that we decide to design a Mark I TRF AM tube tuner
kit designed solely for more local, higher power stations (thus the
sensitivity is less critical than a tuner to also be used for
casual DXing.) How will this further simplify the optimal single
frequency TRF receiver design? Will only one RF amp stage be
necessary, or will we still need two? The focus now will be on very
high-quality audio reproduction of local stations, which I believe
tubeophiles will be most interested in.


Thanks.

Jon Noring

Henry Kolesnik wrote:

How many stages you need depends on the selectivity you need because
of your geographic location and antenna. Two stations close in
frequency will interfere with each other unless you have enough
selectivity. A weak local station that is strong enough to be heard
may get splatter from a distance station close in frequency that has
50KW or more and a pattern that concentrates on your area! High Q,
double tuning, addtional stages all add to selectivity. The superhet
solved this problem.

Hmmm, the "channel TRF" approach may help with one stage selectivity
since it appears we can now use a perfectly optimized higher order
tuned filter on the channel mini-board, while in a traditionally tuned
circuit, implementing that same bandpass circuit to apply across the
whole BCB will be much more difficult, and I would guess be near
impossible (too many circuit components which need to be varied
simultaneously as one varies the reception center frequency.)

With the channel TRF approach, the tube-o-phile can mix and match
bandpass filter types from station to station depending upon the
circumstances. For example, they could use the default, wider-band,
gentler, bandpass filter plug-in board (one which has better linear
phase) for a local station which doesn't have adjacent interference,
and for a more difficult station (with adjacent interference) they can
use a bandpass filter plug-in board with a shape factor closer to
unity (which probably has more ripple and worse linear phase). (Even
for the default "wider-band" filter, because we can now use a
frequency optimized higher order filter, we should be able to achieve
reasonably good selectivity, at least sufficient for local station
reception, even with one RF amp stage.)

There appears to be a lot more freedom given to the circuit designer
when the necessity of tuning a fixed set of tuning components over a
frequency range is removed, such as using higher order bandpass
filters. (Of course, this is one reason for IF, but even superhets
have at least one tuned RF amp before the mixer, so the same issue
applies to superhets, but is not as critical.)

I now wonder that with a single TRF RF amp stage, and with a higher
order bandpass filter optimized for a particular frequency, if we can
now dispense with the RF transformer? Or does an RF transformer confer
other benefits that it should remain? I thought its main benefit was
for improved bandpass shaping, but then I may be wrong here (likely
with high probablity -- RF transformers do help with isolation of
stages for DC, so I've read, but don't know how that would benefit
real tuner circuit design.)

Jon Noring

In article ,
"Henry Kolesnik" wrote:

How many stages you need depends on the selectivity you need because of your
geographic location and antenna

snip

Please don't cross post to rec.radio.shorwave.

--
Telamon
Ventura, California

In article , wrote:

*****

I do have a couple questions of both John and Patrick (and anyone else
caring to chime in) related to this.

1) In the single frequency TRF tube receiver (a TRF designed strictly
to listen to a single frequency), is there a need for double tuned
circuits? Or will singly tuned circuits be sufficient for
excellent performance (audio quality, sensitivity and
selectivity)? If not, how do double tuned circuits benefit the
overall performance of the single frequency TRF receiver?

The advantage of the double tuned circuit over two single tuned circuits
is that it has a better shape factor, the pass band response is flatter.
This advantage applies to single frequency as well as tunable receivers.
Even better response curves can be achieved with three, four, or even six
section filters.


Regards,

John Byrns


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

In article ,
(John Byrns) wrote:

Please delete rec.radio.shortwave from the news group header.

Thanks.

--
Telamon
Ventura, California

John Byrns wrote:
Jon Noring asked a novice question:

[About double tuned versus single tuned circuits]

The advantage of the double tuned circuit over two single tuned
circuits is that it has a better shape factor, the pass band
response is flatter. This advantage applies to single frequency as
well as tunable receivers. Even better response curves can be
achieved with three, four, or even six section filters.

I should have figured this out -- I confused the terminology with
something else.

It does appear that in a single frequency TRF tube tuner, one has an
extensive list of bandpass filter options, both in order (how many
caps and inductors) and basic type (e.g., Butterworth, Bessel,
Chebychev, etc.).

But in a traditional continuously tuned circuit, whether single or
double, it does not appear possible to get anywhere near the optimum
bandpass filter shape for any particular receiver frequency -- with
fairly non-uniform results across the whole BCB, especially if tuning
is done with a multiganged variable capacitor rather than a multigang
variable inductor (permeability tuner).

I guess the question to ask is how much better can be done when
continuous tuning is eliminated, and one uses an optimum bandpass
circuit for each channel frequency? (It appears possible to get almost
uniform bandwidth and shape across the entire BCB spectrum.) For
high-fidelity audio purposes in the channel TRF concept, what order
and type of RF bandpass filter circuitry suggests itself?

Jon

Jon Noring wrote:


I guess the question to ask is how much better can be done when
continuous tuning is eliminated, and one uses an optimum bandpass
circuit for each channel frequency? (It appears possible to get almost
uniform bandwidth and shape across the entire BCB spectrum.) For
high-fidelity audio purposes in the channel TRF concept, what order
and type of RF bandpass filter circuitry suggests itself?



The upside of several single channel TRF circuits is that each channel's
TRF circuits can
be custom tuned for frequency and bandwidth. The downside is that this
will require
a lot of parts for more than a few selected channels, and that if
someone moves to another
radio market a lot of retuning is required if all channels aren't built
to begin with.

As to the question of what the unused channels will do to the receiver,
I'd do the
switching such that all unused channel circuits are completely switched
out, and
maybe tied to ground. The modified turret TV tuner would accomplish
this easily
enough.

Robert Casey wrote:
Jon Noring wrote:

I guess the question to ask is how much better can be done when
continuous tuning is eliminated, and one uses an optimum bandpass
circuit for each channel frequency? (It appears possible to get
almost uniform bandwidth and shape across the entire BCB spectrum.)
For high-fidelity audio purposes in the channel TRF concept, what
order and type of RF bandpass filter circuitry suggests itself?

The upside of several single channel TRF circuits is that each
channel's TRF circuits can be custom tuned for frequency and
bandwidth. The downside is that this will require a lot of parts
for more than a few selected channels, and that if someone moves to
another radio market a lot of retuning is required if all channels
aren't built to begin with.

Yes, this is a downside, but as I see it now, it may not be that much
of a burden -- it depends upon the use. It also opens up many
interesting opportunities for the hobbyist.

There are two general approaches to wiring up the independent bandpass
filters for some or all of the BCB channels:

1) Hardwire all the filter components for all the BCB channels onto
one large board (we'd have an "American" board and a "European"
board, both premade PCB.) This is not trivial, and we could have
upwards of 1000 small RLC components needing to be soldered on the
board, depending upon the order of the filter we want to use.
That's a whole lot of work. It is also inflexible -- the whole
board must be committed to one particular bandpass filter type and
order (e.g., it must be a 4th order Butterworth -- bandwidth is
adjusted by altering the values of the components soldered in as
the supplied "chart" will indicate.)

2) The mini-board idea, where the filter components for a single
channel frequency are put onto a small PCB mini-board. The user
plugs the mini-board into a slot to connect it to the RF amp
section (probably with antenna tuning as well.) We could imagine
having a large PCB "motherboard" which has up to 130+ plugin slots
(not unlike those used for PCs, but we need only have a small
number of contacts per slot -- the number I can't guess at the
moment.) A switch will also be needed (is an electronic switch a
possibility?) Of course, a smaller board with 20 slots, with a
twenty position switch, could be made for those who do not
anticipate tuning anymore than 20 channels. For local listening
(especially for the simple 1 RF amp stage tuner where it won't
be very sensitive), this is probably more than enough channels.

The advantage of this approach is that the user needs only to get
boards for the BCB channels they will listen to, and will have the
ability to alter the bandpass characteristics for a particular
channel (just wire up a different mini-board tuned to that
frequency.) For example, one could have a 7th order Chebychev for
1130 khz with a bandwidth of 15 khz, and a 4th order Butterworth
for 750 khz with a bandwidth of 10 khz. At a later time, the user
can change the bandpass filter used for any particular channel --
just swap mini-boards.

Now how big does the mini-board have to be? I don't have a good
feel for this, while the experienced radio builders out there will
have a much better idea. But let's look at what the mini-board
will contain. Essentially it will contain the RLC bandpass filter
components (plus a trimmer or two for fine calibration of the
center frequency). Depending upon the order of the filter used,
it may have anywhere from 5 to 10 RLC components (again just a
guess -- the very high order bandpass filters will have more.) So
the mini-board will need to be big enough to hold these components.
Again, I think most of them will be fairly small in size, so it is
not inconceivable for the mini-board to be as small as, for
example, 1" x 2" (again, only a guess -- anyone?)

I also foresee that there will be a standard bandpass filter for
the channel TRF tube tuner (a given type and order -- what would
you use for a single RF amp TRF tube tuner for local listening?)
One can have a large number of PCB boards made for that bandpass
filter. Then, for a given channel frequency (e.g., 830 khz), and
a chosen desired bandwidth, the kit-builder refers to the table of
values for each component (e.g., this resistor will be 50 ohms,
that capacitor 5 pf, etc.), solders them in, then fine calibrates
the center frequency. I don't imagine these boards, when made in
bulk, will be that expensive, neither the components be, nor will
it take much time to solder the components onto the mini-board --
maybe only a few minutes.

The biggest issue I foresee is the fine calibration of the bandpass
center frequency -- can that be done independent of the tuner (thus
allowing the kit-supplier to make them available on order) or must
the mini-board be plugged into the tuner? Since there will be some
distance between the RF amp tubes and the bandpass filter, with
intervening wire, a switch or two, and slot connectors, there will
be interwire resistance, capacitance, etc. For a real world tuner,
how important will this be?


As to the question of what the unused channels will do to the
receiver, I'd do the switching such that all unused channel circuits
are completely switched out, and maybe tied to ground.

Agreed, although there are probably other possibilities.

One interesting aspect of this design is that an enthusiast could add
a more traditional continuous tuner if they wanted to (e.g. with a
multiganged variable air capacitor or inductor -- just build it
separately and plug it into one of the slots.

I really do think there are other interesting things one might do
with the "channel TRF" tuner concept. I think we have just scratched
the surface.

Jon Noring

Robert Casey wrote:

As to the question of what the unused channels will do to the receiver,
I'd do the switching such that all unused channel circuits are
completely switched out, and maybe tied to ground. The
modified turret TV tuner would accomplish this easily enough.

I was considering the topology as well and what occurred to me as (near)
ideal would be the sliding catacombs of a National NC-100 series
receiver - completely isolated; both from successive stages and adjacent
(channel) parts - the only down-side (well two) are the limited number
of channels this would afford (5 - as there are 5 bands / positions);
and finding an NC to convert (gut)... but then you'd have the power
supply, audio, infinite imp. detector, etc. already built...

nah, what a waste of a decent general coverage receiver - never mind...

best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com

I haven't seen a technical reason whatsoever that a single channel TRF
perhaps switchable would have any verifiable advantage over a superhet.
But the thread continues to perhaps imply that there might be something.
Did I miss something? I'd sure like to know.
Tnx
--
73
Hank WD5JFR

"Randy and/or Sherry" wrote in message
...


Robert Casey wrote:

As to the question of what the unused channels will do to the receiver,
I'd do the switching such that all unused channel circuits are
completely switched out, and maybe tied to ground. The
modified turret TV tuner would accomplish this easily enough.

I was considering the topology as well and what occurred to me as (near)
ideal would be the sliding catacombs of a National NC-100 series
receiver - completely isolated; both from successive stages and adjacent
(channel) parts - the only down-side (well two) are the limited number
of channels this would afford (5 - as there are 5 bands / positions);
and finding an NC to convert (gut)... but then you'd have the power
supply, audio, infinite imp. detector, etc. already built...

nah, what a waste of a decent general coverage receiver - never mind...

best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com