"Roy Lewallen" wrote in message
...
As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.


It was actually posited in a presentation in 1935. See Wikipedia entry on
FM.

On Thu, 13 Nov 2003 17:33:19 -0800, Roy Lewallen
wrote:

As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.

Roy Lewallen, W7EL

Roy-

Armstrong's classic paper "A Method of Reducing Disturbances in Radio
Signaling by a System of Frequency Modulation" was published in 1936
in the November Proc. IRE. (The paper was presented in a demonstration
at the Nov 1935 IRE New York meeting.)

His field work started 1934, at 44 MHz, with a 2KW 44 MHz transmitter
on the Empire State Building shortly thereafter (the article is a bit
vague on the timing of this part of his operation). (Also, the
frequency was changed to 41 MHz at some point during the trials.)

Armstrong also notes the problem with receiver RF amplifiers at this
frequency and thanks RCA for its provision of experimental VHF
receiving tubes.

His detector circuit looks like a conventional discriminator to me;
two detectors each coupled to a tuned circuit with the outputs summed.
One detector gives + and the other a - output. One tuned circuit
resonates on the high side of the IF passband the the other on the low
side. Each detector fed by an independent buffer amplifier. The
receiver was a double conversion, with the first IF at 6 MHz and the
second IF (and detection) at 400 KHz and a passband of 150 KHz.


Jack K8ZOA

In article , Jack Smith
writes:

On Thu, 13 Nov 2003 17:33:19 -0800, Roy Lewallen
wrote:

As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.

Roy Lewallen, W7EL

Roy-

Armstrong's classic paper "A Method of Reducing Disturbances in Radio
Signaling by a System of Frequency Modulation" was published in 1936
in the November Proc. IRE. (The paper was presented in a demonstration
at the Nov 1935 IRE New York meeting.)

His field work started 1934, at 44 MHz, with a 2KW 44 MHz transmitter
on the Empire State Building shortly thereafter (the article is a bit
vague on the timing of this part of his operation). (Also, the
frequency was changed to 41 MHz at some point during the trials.)

Armstrong also notes the problem with receiver RF amplifiers at this
frequency and thanks RCA for its provision of experimental VHF
receiving tubes.

His detector circuit looks like a conventional discriminator to me;
two detectors each coupled to a tuned circuit with the outputs summed.
One detector gives + and the other a - output. One tuned circuit
resonates on the high side of the IF passband the the other on the low
side. Each detector fed by an independent buffer amplifier. The
receiver was a double conversion, with the first IF at 6 MHz and the
second IF (and detection) at 400 KHz and a passband of 150 KHz.

It's not necessary to go back to just a few years after the first
audion. :-)

The Galvin/Motorola SCR-300/BC-1000 used 7-pin glass base
"miniature" tubes, battery type filaments, and was 40 to 48 MHz.
Tube types were 3A4, 1T4, 1R5 in the VHF range. It started into
full production in 1942 and about 50,000 were built. FM. Dan
Noble migrated to Chicago to work for Galvin in 1940...after finishing
a design for the first mobile police radios...pictures show those
tubes to be glass, octal-base. Noble is the chief architect of the
SCR-300 walkie-talkie. Interesting little gem of a then-tiny
transceiver.

The argument against that might be that 1942 was "after" the entry
into WW2. But...those battery-filament (directly heated) tubes
were in existance in late 1939. Galvin/Motorola used them in the
SCR-536/BC-611, the HF-range "handie-talkie" which was started
in design in 1940.

Perusing the MIT "Rad Lab" volumes ("Amplifiers" is the one I have)
will show that 6AG5s were already around for radar set IF strips
of 30 and 60 MHz. Another 7-pin all-glass "miniature" envelope but
with an indirectly-heated cathode. See also the 6AK5. Both are
the "short" version (physically short compared to the "All-American
Five" types with 7-pin bases and all-glass).

One of the reasons one didn't see those (then) advanced tubes was
that the consumer market products still went in for the cheaper
octal base kind...sockets were also cheaper, many being made out
of melamine-laminate stamp-outs riveted together to hold individual
tube pin grabbers (first cousin to solderless joining gadgets). Most
of the consumer radio equipment of the pre-1950 era were indeed
low-quality "Model T" kind of things.

In pre-WW2 days, a 7-pin all-glass envelope for a tube cost more to
produce than the older octal base with pins soldered to tube
element leads. All metal envelope tubes cost more than glass
envelope types. Once tube makers ramped up for the all-glass
7- and 9-pin little ones, they got cheaper and were used in post-
war consumer radios.

EVERYTHING in radio was already in continuous change from the
1930s onward...even if it didn't show up in the consumer marketplace
right away.

I suppose it is very interesting for antique boatanchor folks to play
with those "stone-age" tubes. Ho hum, I say to self, broke into
vacuum tubes using a 201A from an ancient radio. Phooey. :-)
My wife often uses a little AM-FM set with ear-bud listening things,
the set about the size of a cosmetic compact case. Was a Give-
Away sales promotion thing in the mail. Cost nothing. Obviously
no tubes in it. Fine FM, including stereo sound.

Len Anderson
retired (from regular hours) electronic engineer person

"Avery Fineman" wrote in message
...
It's not necessary to go back to just a few years after the first
audion. :-)

The Galvin/Motorola SCR-300/BC-1000 used 7-pin glass base
"miniature" tubes, battery type filaments, and was 40 to 48 MHz.
Tube types were 3A4, 1T4, 1R5 in the VHF range.

My Feb. 1942 "FM" magazine has an ad from REL selling FM mobiles for police
use. I assume the ad was bought in 1941.

A young engineer who worked for my father at the US Patent Office had one of
the MW (AM broadcast) RCA "camera-case" radios about 1940. It was based on
the tubes mentioned above. Size was about 2x4x8 inches. Most of the space
was taken up by the batteries. The A (filament) batteries lasted about 3
hours.

I estimate the date since this fellow went on active duty with the Navy
_before_ Pearl Harbor. In fact, he phoned my father with details of the
losses at Pearl the next day (Monday, Dec 8, 1941). Those details were kept
VERY secret for at least 2 or 3 years. My father kept the secret, and I
think complained to the Navy about the security breach. Apparently nothing
happened to the fellow who spilt the beans.

"Avery Fineman" wrote in message
...
It's not necessary to go back to just a few years after the first
audion. :-)

The Galvin/Motorola SCR-300/BC-1000 used 7-pin glass base
"miniature" tubes, battery type filaments, and was 40 to 48 MHz.
Tube types were 3A4, 1T4, 1R5 in the VHF range.

My Feb. 1942 "FM" magazine has an ad from REL selling FM mobiles for police
use. I assume the ad was bought in 1941.

A young engineer who worked for my father at the US Patent Office had one of
the MW (AM broadcast) RCA "camera-case" radios about 1940. It was based on
the tubes mentioned above. Size was about 2x4x8 inches. Most of the space
was taken up by the batteries. The A (filament) batteries lasted about 3
hours.

I estimate the date since this fellow went on active duty with the Navy
_before_ Pearl Harbor. In fact, he phoned my father with details of the
losses at Pearl the next day (Monday, Dec 8, 1941). Those details were kept
VERY secret for at least 2 or 3 years. My father kept the secret, and I
think complained to the Navy about the security breach. Apparently nothing
happened to the fellow who spilt the beans.

In article , Jack Smith
writes:

On Thu, 13 Nov 2003 17:33:19 -0800, Roy Lewallen
wrote:

As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.

Roy Lewallen, W7EL

Roy-

Armstrong's classic paper "A Method of Reducing Disturbances in Radio
Signaling by a System of Frequency Modulation" was published in 1936
in the November Proc. IRE. (The paper was presented in a demonstration
at the Nov 1935 IRE New York meeting.)

His field work started 1934, at 44 MHz, with a 2KW 44 MHz transmitter
on the Empire State Building shortly thereafter (the article is a bit
vague on the timing of this part of his operation). (Also, the
frequency was changed to 41 MHz at some point during the trials.)

Armstrong also notes the problem with receiver RF amplifiers at this
frequency and thanks RCA for its provision of experimental VHF
receiving tubes.

His detector circuit looks like a conventional discriminator to me;
two detectors each coupled to a tuned circuit with the outputs summed.
One detector gives + and the other a - output. One tuned circuit
resonates on the high side of the IF passband the the other on the low
side. Each detector fed by an independent buffer amplifier. The
receiver was a double conversion, with the first IF at 6 MHz and the
second IF (and detection) at 400 KHz and a passband of 150 KHz.

It's not necessary to go back to just a few years after the first
audion. :-)

The Galvin/Motorola SCR-300/BC-1000 used 7-pin glass base
"miniature" tubes, battery type filaments, and was 40 to 48 MHz.
Tube types were 3A4, 1T4, 1R5 in the VHF range. It started into
full production in 1942 and about 50,000 were built. FM. Dan
Noble migrated to Chicago to work for Galvin in 1940...after finishing
a design for the first mobile police radios...pictures show those
tubes to be glass, octal-base. Noble is the chief architect of the
SCR-300 walkie-talkie. Interesting little gem of a then-tiny
transceiver.

The argument against that might be that 1942 was "after" the entry
into WW2. But...those battery-filament (directly heated) tubes
were in existance in late 1939. Galvin/Motorola used them in the
SCR-536/BC-611, the HF-range "handie-talkie" which was started
in design in 1940.

Perusing the MIT "Rad Lab" volumes ("Amplifiers" is the one I have)
will show that 6AG5s were already around for radar set IF strips
of 30 and 60 MHz. Another 7-pin all-glass "miniature" envelope but
with an indirectly-heated cathode. See also the 6AK5. Both are
the "short" version (physically short compared to the "All-American
Five" types with 7-pin bases and all-glass).

One of the reasons one didn't see those (then) advanced tubes was
that the consumer market products still went in for the cheaper
octal base kind...sockets were also cheaper, many being made out
of melamine-laminate stamp-outs riveted together to hold individual
tube pin grabbers (first cousin to solderless joining gadgets). Most
of the consumer radio equipment of the pre-1950 era were indeed
low-quality "Model T" kind of things.

In pre-WW2 days, a 7-pin all-glass envelope for a tube cost more to
produce than the older octal base with pins soldered to tube
element leads. All metal envelope tubes cost more than glass
envelope types. Once tube makers ramped up for the all-glass
7- and 9-pin little ones, they got cheaper and were used in post-
war consumer radios.

EVERYTHING in radio was already in continuous change from the
1930s onward...even if it didn't show up in the consumer marketplace
right away.

I suppose it is very interesting for antique boatanchor folks to play
with those "stone-age" tubes. Ho hum, I say to self, broke into
vacuum tubes using a 201A from an ancient radio. Phooey. :-)
My wife often uses a little AM-FM set with ear-bud listening things,
the set about the size of a cosmetic compact case. Was a Give-
Away sales promotion thing in the mail. Cost nothing. Obviously
no tubes in it. Fine FM, including stereo sound.

Len Anderson
retired (from regular hours) electronic engineer person

On Thu, 13 Nov 2003 17:33:19 -0800, Roy Lewallen
wrote:

As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.

Roy Lewallen, W7EL

Roy-

Armstrong's classic paper "A Method of Reducing Disturbances in Radio
Signaling by a System of Frequency Modulation" was published in 1936
in the November Proc. IRE. (The paper was presented in a demonstration
at the Nov 1935 IRE New York meeting.)

His field work started 1934, at 44 MHz, with a 2KW 44 MHz transmitter
on the Empire State Building shortly thereafter (the article is a bit
vague on the timing of this part of his operation). (Also, the
frequency was changed to 41 MHz at some point during the trials.)

Armstrong also notes the problem with receiver RF amplifiers at this
frequency and thanks RCA for its provision of experimental VHF
receiving tubes.

His detector circuit looks like a conventional discriminator to me;
two detectors each coupled to a tuned circuit with the outputs summed.
One detector gives + and the other a - output. One tuned circuit
resonates on the high side of the IF passband the the other on the low
side. Each detector fed by an independent buffer amplifier. The
receiver was a double conversion, with the first IF at 6 MHz and the
second IF (and detection) at 400 KHz and a passband of 150 KHz.


Jack K8ZOA

There is no problem doing that. Realize that the 'modern' miniature tubes
of the 1950s that were used to make FM tuners are internally identical to
the old tubes from the 1930s.

You use a 6K7 instead of a 6SG7 for instance. Or if you want to go even
older, a 36 I think. A 27 instead of a 6AT6 (triode section).

The lead lengths are longer and might require a bit more care in layout but
it should be okay. Just look at the Hallicrafters S-27 for some ideas.

Bob

To my simple mind, the technology is essentially the same between prewar FM
and "new" FM. You would change some coils & whatnot, primarily in the front
end (experts, chime in here as usual to correct my habitual blunders :-), to
receive and decode the same kind of signal, only in a different frequency
band. You would also want a dipole antenna of slightly different size than
what's used now. Otherwise, I see nothing to prevent you from building a
"new FM" receiver using prewar components.

Phil

David Forsyth wrote:

Would it be possible, though not necessarily practical, to make a receiver
for the modern FM broadcast band, using only pre-WWII tube technology? I
know they had FM on a lower frequency band at that time.

I have a few pre war FM sets, see
http://www.geocities.com/wa2ise/radios/fm45.html

What sorts of
tubes could one use from the 1930's to make a receiver that could tune in
the modern FM band?

Focus on the front end. Once you get to the IF, then my Emerson 460 pre
war set
would have the same technology as your "what if" set. I think acorn
tubes were pre war,
and were designed for VHF service. 2 or 3 such tubes (one RF amp,
another local
osc, and the 3rd the mixer) should make a good 100MHz front end. The
above Emerson
had an IF around 4 or was it 8 MHz, used octal tubes like 6SG7 and 6SH7
and a 6H6
for an FM detector.