+7dB from BFO to diode ring mixer?
 

hello,

can someone please explain me, what does it mean that DBM diode ring
mixer expects +7dB from BFO?

I do understand that from BFO comes out some peak-to-peak voltage (2.2
volts for example).
But how does it scale to +7dB?

thanks

+7dB from BFO to diode ring mixer?
 

hi.
it's not dB, it's dBm and it's a measure of power. the diode mixer has
a finite input resistance (read also impedance). as such a voltage
applied to its input causes power to be generated and consumed there. 0
dBm is defined to be 1mW of power into 50 ohms. 7dBm equates to 5mW of
power into a load of 50 ohms. this amounts to 500mV RMS, or
approximately 1.5 volts PTP across 50 ohms.
so you have to produce 5 mW of power to drive a regular DBM . there are
also special ones requiring up to 50 mW or more for proper performance.
Hope it helps:
Saandy 4Z5KS





wrote:
hello,

can someone please explain me, what does it mean that DBM diode ring
mixer expects +7dB from BFO?

I do understand that from BFO comes out some peak-to-peak voltage (2.2
volts for example).
But how does it scale to +7dB?

thanks

+7dB from BFO to diode ring mixer?
 

hi Saandy,

I was not aware of the '0 dBm is defined to be 1mW of power into 50
ohms' part.
Rest of calculations were perfrectly understood ;)

thank you for your assistance!

+7dB from BFO to diode ring mixer?
 

wrote:

hi Saandy,

I was not aware of the '0 dBm is defined to be 1mW of power into 50
ohms' part.
Rest of calculations were perfrectly understood ;)

thank you for your assistance!

There are various dBx measures of real signal characteristics. The most
common ones that I know of are dBm (dB over 1mW), dBV (dB over 1V,
presumably ignoring impedance and therefore really just a fancy-pants
amplitude measure) and dBc (dB under carrier, very important stuff to
measure phase noise in an oscillator or transmitter).

Presumably you could define the 'x' in dBx to be anything -- if you were
married many times, for instance, dBxmil would be a measure of the
number of ex mothers-in-law you have in the room with you, but I'm not
sure if that should be 10 log (N) or 20 log (N).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

+7dB from BFO to diode ring mixer?
 

Tim Wescott writes:

Presumably you could define the 'x' in dBx to be anything -- if you
were married many times, for instance, dBxmil would be a measure of
the number of ex mothers-in-law you have in the room with you, but I'm
not sure if that should be 10 log (N) or 20 log (N).


Well, since the primary charactersitic of mothers-in-law is their
volume, it should be 30 log HIHI

--
73 de N1GAK/XE2
echo ' | sed s/aba/c/g

+7dB from BFO to diode ring mixer?
 

There are various dBx measures of real signal characteristics. The most
common ones that I know of are dBm (dB over 1mW), dBV (dB over 1V,
presumably ignoring impedance and therefore really just a fancy-pants
amplitude measure) and dBc (dB under carrier, very important stuff to
measure phase noise in an oscillator or transmitter).
======================================
RF power limitations (power into antenna) for the UK amateur radio
licences are expressed in dBW 26 dBW equals 400 Watts
15 dBW equals 32 Watts etc .

Frank GM0CSZ / KN6WH

+7dB from BFO to diode ring mixer?
 

Highland Ham wrote:
There are various dBx measures of real signal characteristics. The
most common ones that I know of are dBm (dB over 1mW), dBV (dB over
1V, presumably ignoring impedance and therefore really just a
fancy-pants amplitude measure) and dBc (dB under carrier, very
important stuff to measure phase noise in an oscillator or transmitter).

======================================
RF power limitations (power into antenna) for the UK amateur radio
licences are expressed in dBW 26 dBW equals 400 Watts
15 dBW equals 32 Watts etc .

Frank GM0CSZ / KN6WH
Why not just say Watts or milliwatts and be done with it?
Why drag dB into it?

BTW dB means deci-bell, why not use a WHOLE BELL.
(and the brass figligee with bronze oak-leaf palm to anybody
who can guess who this unit of measure was named after!)

+7dB from BFO to diode ring mixer?
 

Ken Scharf wrote:

RF power limitations (power into antenna) for the UK amateur radio
licences are expressed in dBW 26 dBW equals 400 Watts
15 dBW equals 32 Watts etc .

Why not just say Watts or milliwatts and be done with it?
Why drag dB into it?

Maybe because dB gives you a better idea of the limited communications
benefit to be achieved by turning up the power?

It also simplifies factoring in antenna gain, feadline loss, etc...

Really this is same idea as using a sliderule - take the log of
everything and then gain/loss becomes simple addition subtraction.

One downside though is that when playing around with a signal generator
calibrated in dB, you can fail to appreciate the degree to which you
may be turning up the power to something under test, at least until you
get used to the numbers.

+7dB from BFO to diode ring mixer?
 

Ken Scharf wrote:
Highland Ham wrote:
There are various dBx measures of real signal characteristics. The
most common ones that I know of are dBm (dB over 1mW), dBV (dB over
1V, presumably ignoring impedance and therefore really just a
fancy-pants amplitude measure) and dBc (dB under carrier, very
important stuff to measure phase noise in an oscillator or transmitter).
======================================
RF power limitations (power into antenna) for the UK amateur radio
licences are expressed in dBW 26 dBW equals 400 Watts
15 dBW equals 32 Watts etc .

Frank GM0CSZ / KN6WH
Why not just say Watts or milliwatts and be done with it?
Why drag dB into it?
====================================
Just ask the UK licensing authority

Frank GM0CSZ / KN6WH

+7dB from BFO to diode ring mixer?
 

Ken Scharf wrote:

BTW dB means deci-bell, why not use a WHOLE BELL.
(and the brass figligee with bronze oak-leaf palm to anybody
who can guess who this unit of measure was named after!)


Well, it wasn't named after Watson, so that only leaves one man...


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

+7dB from BFO to diode ring mixer?
 

Michael A. Terrell wrote:

Ken Scharf wrote:

BTW dB means deci-bell, why not use a WHOLE BELL.
(and the brass figligee with bronze oak-leaf palm to anybody
who can guess who this unit of measure was named after!)



Well, it wasn't named after Watson, so that only leaves one man...




Art Bell?

-ex

+7dB from BFO to diode ring mixer?
 

"Steve Nosko" wrote in message
...
Actually I believe the unit is a Bel. Yes 10 dB is one Bel. For some
reason nobody uses the bel...or for that matter the milibel, microbel,

This may interest some.
I believe, although can't find the actual reference now, that the decibel
was used rather than the bel from the start because the numbers were very
close to those of the m.s.c. used before it.
The following are from "Signal Training" Vol 2, Part 3 (Line telephony and
Telegraphy) 1936, HMSO, an Army training manual:-

" The decibel.- The standard unit for measurement of telephone transmission
in this country [UK] is now the decibel, which is one-tenth of a bel, and
has superseded the mile of standard cable."

and

"1 decibel = 1.084 m.s.c. = 1.151 decineper"
"1 m.s.c. = 0.9221 decibel = 1.0616 necineper"

and just to explain the decineper

"In the majority of European countries the unit of measurement for telephone
transmission is the decineper, which is one-tenth of one Neper. The unit is
named after Napier, the originator of Naperian or natural logarithms, i.e.
logarithms to the base e. The neper is a measurement of the total
attenuation and can be defined as the natural logarithm of the ratio of the
currents at two different points in a network or apparatus, or as half the
natural logarithm of the ratio of powers at two different points in a
network or apparatus."


The book doesn't show an upper case B for Bel in db so that must have come
later but it does use the plural as in "30dbs" so should we be using dbuVs
etc? I've used an artificial cable box for 75 ohm video but have never seen
a reference m.s.c., originally an actual lump of cable but later a series of
switched networks.

John
MW1FGQ