Some of the schematic diagrams of war times radios - though not all of them -
adopt an odd way of identifying resistance values.

For instance a 200.000 ohm resistor is marked "200 Mohm". The "M" means kilo,
not mega! Conversely a 2.000.000 ohm resistor is marked "2 Megaohm".

Does any one know the origin of this way of marking resistors and when it was
abandoned?

73

Tony I0JX
Rome. Italy

In "Antonio Vernucci"
wrote:

Does any one know the origin of this way of marking resistors and when
it was abandoned?

It was based on the Roman numeral "M" representing 1,000, but I don't
know when it stopped being used.

I still see "M" being used to represent thousands of dollars, and MCF is
still a pretty standard representation of "thousand cubic feet" of
natural gas.

--
Bert Hyman W0RSB St. Paul, MN

It was based on the Roman numeral "M" representing 1,000, but I don't
know when it stopped being used.

Living in Rome, I should have known... hi.

I have a diagram dated 1953 in which M still represents 1000. In that diagram
they use MF for microfarad (on the other hand a thousand farad would not make
sense).

I still see "M" being used to represent thousands of dollars, and MCF is
still a pretty standard representation of "thousand cubic feet" of
natural gas.

Good to know, I would not have suspected that M$ could mean just a thousand
dollars and not a million dollars. We here commonly use MEuro for million Euro.

Thanks & 73
Tony I0JX

Edmund H. Ramm wrote:

In "Antonio Vernucci"
writes:

[...]
I have a diagram dated 1953 in which M still represents 1000. In
that diagram they use MF for microfarad
[...]

There are also diagrams where m (milli, 10^-3) is used to
represent mikro (10^-6). Even worse and confusing are those, where
mmF gets used when pF (pico, 10^-12) is meant.

Huh? What's confusing about micro-micro farads? :-):-)
--
Robert (Bob) Smits, VE7HS & Linux Fan

"Bob Smits" ha scritto nel messaggio
news:HbmdncivItyZOM7RnZ2dnUVZ_uqdnZ2d@islandhostin g.com...
Edmund H. Ramm wrote:

In "Antonio Vernucci"
writes:

[...]
I have a diagram dated 1953 in which M still represents 1000. In
that diagram they use MF for microfarad
[...]

There are also diagrams where m (milli, 10^-3) is used to
represent mikro (10^-6). Even worse and confusing are those, where
mmF gets used when pF (pico, 10^-12) is meant.

Huh? What's confusing about micro-micro farads? :-):-)
--
Robert (Bob) Smits, VE7HS & Linux Fan


Among the odd markings:

- in the 60ies it was fairly common to use kpF (kilopicofarad) to mean nF
(nanofarad)
- in the 30ies, German power mica capacitors were marked in centimeters (cm). 1
cm is equal to about 1.1 pF

73

Tony I0JX

"Antonio Vernucci" wrote in message
...
"Bob Smits" ha scritto nel messaggio
news:HbmdncivItyZOM7RnZ2dnUVZ_uqdnZ2d@islandhostin g.com...
Edmund H. Ramm wrote:

In "Antonio Vernucci"
writes:

[...]
I have a diagram dated 1953 in which M still represents 1000. In
that diagram they use MF for microfarad
[...]

There are also diagrams where m (milli, 10^-3) is used to
represent mikro (10^-6). Even worse and confusing are those, where
mmF gets used when pF (pico, 10^-12) is meant.

Huh? What's confusing about micro-micro farads? :-):-)
--
Robert (Bob) Smits, VE7HS & Linux Fan


Among the odd markings:

- in the 60ies it was fairly common to use kpF (kilopicofarad) to mean nF
(nanofarad)
- in the 30ies, German power mica capacitors were marked in centimeters
(cm). 1 cm is equal to about 1.1 pF

73

Tony I0JX


and cps instead of Hertz
Ah...those were the good ol' days

- in the 60ies it was fairly common to use kpF (kilopicofarad) to mean nF
(nanofarad)

Never saw that before.


it was not just on the doagrams. I have some capacitors marked that way...

73

Tony I0JX

Well, "m" is reserved for "milli". Using a QWERTY typewriter (remember
them?) or ASCII computer keyboard IMO "u" is the better substitute for
"micron". But "p" and "n" are on all those keyboards. So there was/is
no need for the above "mmF" construct, or awkward notations like .005uF
when 5nF would say it much nicer.

73, Eddi ._._.
--

Yes, but for some reason 5nF was not of common use before about 25 years ago.
..005uF or 5kpF was the standard, who knows why..

Tony I0JX

In message , Antonio
Vernucci writes
Well, "m" is reserved for "milli". Using a QWERTY typewriter (remember
them?) or ASCII computer keyboard IMO "u" is the better substitute for
"micron". But "p" and "n" are on all those keyboards. So there was/is
no need for the above "mmF" construct, or awkward notations like .005uF
when 5nF would say it much nicer.

73, Eddi ._._.
--

Yes, but for some reason 5nF was not of common use before about 25
years ago. .005uF or 5kpF was the standard, who knows why..

For some reason, Americans find the British use of 'puff' and 'puffs'
(the colloquial 'pronunciation' of 'pF') highly amusing!
--
Ian