Maker Pro
Login Join Maker Pro
Or sign in with

Menu

Connect With Us

Network

Maker Pro

substituting old IF cans

A

asdf

Suppose you're designing an AM-FM radio just for fun and the old way,
ie no specialized integrated circuits; how would you substitute the old
455/460 KHz and 10.7 MHz IF transformers that are getting hard to find?
Hand wound toroids plus capacitive trimmers? Untuned stages w/crystal
filters?
 
A

asdf

I have no idea what's available today, but if you look at my recently
posted parts bin list, there were 455kHz ceramic interstage filters and
emitter bypasses (from BJT days ;-)

I would imagine the interstages could be used with modern chips... maybe
even OpAmps ?:)

For 10.7MHz, maybe there's a SAW filter??
Click to expand...

I still have a few IF cans left from the 90s and could indeed use them
but my goal would be making an old style radio without them. I'll
probably do some tests with non tuned bjt/fet stages coupled through
ceramic filters. Seems doable.
Opamps should also be fine, there are some sold as video amplifiers that
go up to several hundred MHz and more (the LMH6550 looks interesting) but
that would defeat the "old style" requirement:).
 
J

Joerg

asdf said:
I still have a few IF cans left from the 90s and could indeed use them
but my goal would be making an old style radio without them. I'll
probably do some tests with non tuned bjt/fet stages coupled through
ceramic filters. Seems doable.
Opamps should also be fine, there are some sold as video amplifiers that
go up to several hundred MHz and more (the LMH6550 looks interesting) but
that would defeat the "old style" requirement:).
Click to expand...


Ceramic filters aren't "old style" either. They were not available back
then resp. prohibitively expensive.

I guess that leaves you with winding your own filters. Read up about how
they are tapped, and why. How to get the Q high enough and so on. You
might want to also learn about Q-multipliers which are a nice way to run
a filter at a Q that it doesn't really have. Depends on how fancy your
radio should be.

Now if you ever want to build a "new style" radio make sure it has a
difficult to read LCD, consumes oodles of watts, needs a fan, the IM
performance is the pits, AM reception is next to useless, and the
firmware crashes at least once a month requiring a power-cycle :)
 
R

Rich Grise

ChrisQ said:
In fact, ceramic filters *are* quite old hat. Clevite Corp were making
465 or thereabouts Khz ceramic filters back in the early 60's. I used
two in a homebuilt short wave radio around 1963. fwir, they came in D
shaped blue plastic packages. Can't have been that expensive either, as
I would still have been in school at the time.

Of course, the japs took over the market, just like they did in a lot of
other areas...
Click to expand...
Does anybody remember "mechanical filters?" I remember seeing them in the
mid-1960s or so, while they were designing SSB transmitters in "The Radio
Amateurs' Handbook" and various hobbyist magazines. I'm almost sure I've
seen them in the Allied catalog. The ones I remember were centered about
the 455KHz band, which was pretty much standard IF for AM broadcast.

Speaking of old farts, does anybody remember that plug-in audio phase-shift
network that gave two outputs 90 degrees apart from 300 Hz to 3 KHz?

Cheers!
Rich
 
J

Jamie

Rich said:
Does anybody remember "mechanical filters?" I remember seeing them in the
mid-1960s or so, while they were designing SSB transmitters in "The Radio
Amateurs' Handbook" and various hobbyist magazines. I'm almost sure I've
seen them in the Allied catalog. The ones I remember were centered about
the 455KHz band, which was pretty much standard IF for AM broadcast.

Speaking of old farts, does anybody remember that plug-in audio phase-shift
network that gave two outputs 90 degrees apart from 300 Hz to 3 KHz?

Cheers!
Rich
Click to expand...
Yes, I remember that and I am not yet classified old, as you! :)

Jamie
 
M

m II

"Rich Grise" wrote in message
In fact, ceramic filters *are* quite old hat. Clevite Corp were making
465 or thereabouts Khz ceramic filters back in the early 60's. I used
two in a homebuilt short wave radio around 1963. fwir, they came in D
shaped blue plastic packages. Can't have been that expensive either, as
I would still have been in school at the time.

Of course, the japs took over the market, just like they did in a lot of
other areas...
Click to expand...
Does anybody remember "mechanical filters?" I remember seeing them in the
mid-1960s or so, while they were designing SSB transmitters in "The Radio
Amateurs' Handbook" and various hobbyist magazines. I'm almost sure I've
seen them in the Allied catalog. The ones I remember were centered about
the 455KHz band, which was pretty much standard IF for AM broadcast.

Speaking of old farts, does anybody remember that plug-in audio phase-shift
network that gave two outputs 90 degrees apart from 300 Hz to 3 KHz?

Cheers!

---
Your memory is going, also.

Phase shift is relative to the frequency put though the network.

300 Hz to 3 kHz (no cap on "k", it's not a person's name) is a large range
to consider the same phase shift without digital analysis and interference.


mike

Rich
 
W

Warren

Joerg expounded in
...
Now if you ever want to build a "new style" radio make sure
it has a difficult to read LCD, consumes oodles of watts,
needs a fan, the IM performance is the pits, AM reception
is next to useless, and the firmware crashes at least once
a month requiring a power-cycle :)
Click to expand...

Actually, there is also the possibility of making a modern VFO
in your otherwise retro radio.

Consider using an old stepper motor for the tuning control
(more on that below) and obviously a nice LCD with large
lettering for tuning frequency display. AVR or PIC behind
that.

For the tuning control, I've always wanted to put a stepper
motor operated as generator through a zero crossing detector
(or better with hysterisis).

That way as you turn the stepper motor, with attached knob,
into a precise tuning control. Each step produces a nice click
pulse back to the microcontroller to move the local oscillator
so many khz one way or tother.

Make the software smart enough to discern fast rotates (big
steps) and slow turns as little steps in tuning.

For extra marks, add some favourite station buttons. :)

Warren
 
U

[email protected]

Speaking of old farts, does anybody remember that plug-in audio phase-shift
network that gave two outputs 90 degrees apart from 300 Hz to 3 KHz?
Click to expand...

I have also seen some references to such module in ARRL handbooks and
as far as I remember, the type number was in the general format XnXn
(like R2D2), but if I remember correctly, the second X was "Q".
Hopefully this might bring up some memories.

The opposite sideband rejection in a phasing SSB receiver depended
very significantly on the (relative) accuracy of the phasing network
in the I and Q paths.

While it is easy to get resistors with 1 % or even 0.1 % accuracy,
getting capacitors with even 1 % accuracy is hard. In practice, one
needs to buy a batch of capacitors and select pairs with equal (but
not necessary nominal) capacitances, in order to get good opposite
sideband rejection.
 
U

[email protected]

Ceramic filters. Of course, if you want to learn more
about the

Terman's book is available on-line as a PDF, and I'd also point to the old RCA
Radiotron Manual (also available as a PDF). Pete Millett's web site has a
bunch of scans that are quite useful as well:
http://pmillett.com/tubebooks/technical_books_online.htm . There's really a
lot of wisdom in those old books!

---Joel
Click to expand...

For tubes (and high voltage FETs) the circuits are quite straight
forward. For bipolar transistors with very low input and output
impedances, you need to connect the transistor through some
intermediate tap in the resonant circuit inductor.

It is quite trivial to generate a very narrow band filter by simply
cascading multiple resonant circuits (neglecting any temperature
effects) separated by an amplification device (tube/transistor).

However, in order to transfer some useful information, the modulated
carrier also generates sidebands that must be transferred to the
detector. For AM broadcast reception at least 4.5 (or 5 kHz depending
on country) on both sides of the carrier needs to be passed to the
detector.

At 455 kHz IF, one could either use staggered tuning (input resonant
circuit tuned to 453 kHz, output tuned to 457 kHz) or use accurately
controlled coupling/loading between two resonant circuits both tuned
to 455 kHz, creating a double hump passband.
 
U

[email protected]

Look up Image Reject (or SSB) Mixers.

For the audio, ever here of pots ?:)

...Jim Thompson
Click to expand...

Absolutely.

For image rejection mixers, in addition to the carrier 90 degree phase
shift (which is trivial at least for a fixed carrier), but you also
need the 90 degree phase shift across the base band frequency range,
which, unfortunately can be hard, especially, if the relative
frequency range is larger than 1:10 (e.g. 300 Hz .. 3 kHz).
 
J

Joerg

Joel said:
Ah, so you've seen my proposal to get the feds to hand me millions of
dollars to replace the air traffic controller radios from their current
AM implementation to something all digital and highly proprietary then,
yes?

:)
Click to expand...

I think pilots would fight that tooth and nail, because AM just plain
works. In Europe they did that with emergency services, replacing their
traditional FM gear. From what I've heard that has resulted in some
problems.

Of course, consumers just get it over the head. Like with DTV where
every other movie pixelates out and sometimes we can't watch the news
anymore.
 
R

Rich Grise

Joerg said:
Of course, consumers just get it over the head. Like with DTV where
every other movie pixelates out and sometimes we can't watch the news
anymore.
Click to expand...
You need to move closer to the Xmit antenna. ;-)

Cheers!
Rich
 
R

Rich Grise

I have also seen some references to such module in ARRL handbooks and
as far as I remember, the type number was in the general format XnXn
(like R2D2), but if I remember correctly, the second X was "Q".
Hopefully this might bring up some memories.
Click to expand...
ISTR 2Q30 or 3Q4 or so, but it was many many moons ago...

Thanks!
Rich
 
J

Joerg

Rich said:
You need to move closer to the Xmit antenna. ;-)
Click to expand...

The signal is way strong but ATSC stinks under multipath conditions,
which are rather extreme here. But the fact is, NTSC was better because
it always worked.

Then some stations did the unbelievable, gave up their precious VHF
channels for UHF. I will never understand that. This was like trading
your plate of filet mignon against one with macaroni and cheese, but
paying the same price.
 
R

Rich Grise

Joerg said:
Then some stations did the unbelievable, gave up their precious VHF
channels for UHF.
Click to expand...

Wasn't that some imperial edict handed down from "on high"?

Thanks,
Rich
 
S

Sylvia Else

Suppose you're designing an AM-FM radio just for fun and the old way,
Click to expand...

The old way is a TRF receiver, or regenerative circuit.

Superhets are the new-fangled technique.

Sylvia.
 
J

josephkk

Yup. Conceived by Sid Darlington at Bell Labs. (Yes, the same one.)

Anyone have his paper? I seem to have lost/misplaced my copy :-(

...Jim Thompson
Click to expand...

Sid had to crib it from Armstrong, a nearly forgotten man.
 
You must log in or register to reply here.

Similar threads

SparkyCal
Substituting a Capacitor
Replies
3
Views
2K
Audioguru
Audioguru
Apocaloptigon
Substituting a transistor for a MOSFET in a flyback driver
Replies
2
Views
2K
Apocaloptigon
Apocaloptigon
B
Problems substituting a relay
3 4 5
Replies
96
Views
8K
CDRIVE
CDRIVE
P
Substituting OEM only Transistors
Replies
3
Views
2K
(*steve*)
(*steve*)
S
Substituting Lexmark's No 4 and 5 Cartridges
Replies
3
Views
971
neon
neon
Top