measuring signal levels

Hi,

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

Marky P.

On 2007-07-11, Marky P wrote:
Hi,

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

IIRC (which I probably don't)

0 dBV = 30 dBmV = 60 dBuV

0 dBW = 30 dBmW (dBm) = 60 dBuW

Relating dBmV to dBmW depends on the impedence..

--
David Taylor

Marky P wrote:
Hi,

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

Marky P.

You shouldn't really need to worry about conversion unless your talking
to Bill.

Regards
Glenn...

On Wed, 11 Jul 2007 21:11:27 +0100, Usenet
wrote:

Marky P wrote:
Hi,

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

Marky P.

You shouldn't really need to worry about conversion unless your talking
to Bill.

Regards
Glenn...

Well, I've just been reading through (again) Bill's article on
satellite distribution systems and he prefers using dBmv to dbV, but
my Promax meter used dBuV. So really what I want to know (put simply)
is what is the minimum signal strength in dBuv for a reliable signal
(be it DTT, FM, DAB or analogue telly). I measured the analogue
signal of channel 5 on my portable telly (using loop aerial) and meter
reads 46.2 dBuV which provides a perfect picture. Is this a good
level?

Marky P.

David Taylor wrote:

On 2007-07-11, Marky P wrote:
Hi,

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

IIRC (which I probably don't)

0 dBV = 30 dBmV = 60 dBuV

0 dBW = 30 dBmW (dBm) = 60 dBuW

Relating dBmV to dBmW depends on the impedence..


Half right by my reckoning.

0 dBW = 30 dBmW (dBm) = 60 dBuW

right.

0 dBV = 30 dBmV = 60 dBuV

wrong. Should be

0 dBV = 60 dBmV = 120 dBuV.

Note that dB always represents a power ratio. dB = 10*log(P/Pr) where the
log is base 10 (not base e or natural log), P is the power and Pr is the
reference power. Since P = V squared / R, dB = 10*log(V squared / Vr
squared) = 20*log(V/Vr).

Converting dBV to dBW:

At 50 ohms 0 dBV = -17 dBW (1/50 W)

At 75 ohms 0 dBV = -19 dBW (1/75 W)

so not much difference for a co-ax installation.

At 300 ohms 0 dBV = -25 dBW (1/300 W)

From what I remember reading, digital TV (64 QAM, I think) requires 45 dBuV
minimum though this will depend a bit on the receiver. I'd guess that 16
QAM needs about 40 dBuV. Analogue requires 60 dBuV (1 mV or 0 dBmV) for
good reception - I assume this is on the sync pulses but stand open to
correction

Hope this is correct and useful and not just pedantic.

--
----Steve Hayes, South Wales, UK----
Please remove colours from my e-mail address.

Marky P wrote:
On Wed, 11 Jul 2007 21:11:27 +0100, Usenet
wrote:

Marky P wrote:
Hi,

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

Marky P.

You shouldn't really need to worry about conversion unless your talking
to Bill.

Regards
Glenn...

Well, I've just been reading through (again) Bill's article on
satellite distribution systems and he prefers using dBmv to dbV, but
my Promax meter used dBuV.

Can you subtract 60 in your head? That will give you dBmV from dBuV.

So really what I want to know (put simply)
is what is the minimum signal strength in dBuv for a reliable signal
(be it DTT, FM, DAB or analogue telly). I measured the analogue
signal of channel 5 on my portable telly (using loop aerial) and meter
reads 46.2 dBuV which provides a perfect picture. Is this a good
level?
10^(46.2/20) = 204uV. Assuming it's in 75 ohms, that's -62.5dBm, around
40dB above noise in 4MHz bandwidth in a typical receiver. Should be a
cracking picture.

The minimum signal strength needed varies according to the receiver
bandwidth (the modes you list are all different bandwidths), noise
figure and detector characteristics. There isn't a single number.

Steve

Marky P wrote:

On Wed, 11 Jul 2007 21:11:27 +0100, Usenet
wrote:

Marky P wrote:

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

It's just decibels relative to V volts mV millivolts and dBuV
microvolts. The u should be a greek mju.

Well, I've just been reading through (again) Bill's article on
satellite distribution systems and he prefers using dBmv to dbV, but
my Promax meter used dBuV.

I found this http://www.temcom.com/pages/dBCalc_manual.html
--
Phil Cook looking north over the park to the "Westminster Gasworks"

On Wed, 11 Jul 2007 23:05:15 +0100, Steve Hayes
wrote:

David Taylor wrote:

On 2007-07-11, Marky P wrote:
Hi,

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

IIRC (which I probably don't)

0 dBV = 30 dBmV = 60 dBuV

0 dBW = 30 dBmW (dBm) = 60 dBuW

Relating dBmV to dBmW depends on the impedence..


Half right by my reckoning.

0 dBW = 30 dBmW (dBm) = 60 dBuW

right.

0 dBV = 30 dBmV = 60 dBuV

wrong. Should be

0 dBV = 60 dBmV = 120 dBuV.

Note that dB always represents a power ratio. dB = 10*log(P/Pr) where the
log is base 10 (not base e or natural log), P is the power and Pr is the
reference power. Since P = V squared / R, dB = 10*log(V squared / Vr
squared) = 20*log(V/Vr).

Converting dBV to dBW:

At 50 ohms 0 dBV = -17 dBW (1/50 W)

At 75 ohms 0 dBV = -19 dBW (1/75 W)

so not much difference for a co-ax installation.

At 300 ohms 0 dBV = -25 dBW (1/300 W)

From what I remember reading, digital TV (64 QAM, I think) requires 45 dBuV
minimum though this will depend a bit on the receiver. I'd guess that 16
QAM needs about 40 dBuV. Analogue requires 60 dBuV (1 mV or 0 dBmV) for
good reception - I assume this is on the sync pulses but stand open to
correction

Hope this is correct and useful and not just pedantic.

That is very useful. Thanks.

Marky P

On Wed, 11 Jul 2007 23:09:19 +0100, Phil Cook
wrote:

Marky P wrote:

On Wed, 11 Jul 2007 21:11:27 +0100, Usenet
wrote:

Marky P wrote:

I know there are two ways to measure RF signal levels, dBmV & dBV. My
meter uses dBuV. Is that the same as dBV or dBmV? Is there a
conversion chart between the two measurements?

It's just decibels relative to V volts mV millivolts and dBuV
microvolts. The u should be a greek mju.

Well, I've just been reading through (again) Bill's article on
satellite distribution systems and he prefers using dBmv to dbV, but
my Promax meter used dBuV.

I found this http://www.temcom.com/pages/dBCalc_manual.html

Brilliant! Thanks Phil!

Marky P.

On 2007-07-11, Steve Hayes wrote:
David Taylor wrote:

Half right by my reckoning.

0 dBW = 30 dBmW (dBm) = 60 dBuW

right.

0 dBV = 30 dBmV = 60 dBuV

wrong. Should be

0 dBV = 60 dBmV = 120 dBuV.

Note that dB always represents a power ratio. dB = 10*log(P/Pr) where the
log is base 10 (not base e or natural log), P is the power and Pr is the
reference power. Since P = V squared / R, dB = 10*log(V squared / Vr
squared) = 20*log(V/Vr).

Damn. I knew something didn't sound right, but managed to forget the
vital part of the 10log(P/Pr) = 20log(V/Vr) formula...

Converting dBV to dBW:

At 50 ohms 0 dBV = -17 dBW (1/50 W)

At 75 ohms 0 dBV = -19 dBW (1/75 W)

so not much difference for a co-ax installation.

At 300 ohms 0 dBV = -25 dBW (1/300 W)

From what I remember reading, digital TV (64 QAM, I think) requires 45 dBuV
minimum though this will depend a bit on the receiver. I'd guess that 16
QAM needs about 40 dBuV. Analogue requires 60 dBuV (1 mV or 0 dBmV) for
good reception - I assume this is on the sync pulses but stand open to
correction

Hope this is correct and useful and not just pedantic.

Well, it helped refresh my memory a bit, anyway.

--
David Taylor