Home cinema - O.T. Microwaves

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- - O.T. Microwaves (http://www.homecinemabanter.com/showthread.php?t=66795)

In article , tony sayer

wrote:
Domestic microwaves (and many other devices) use the same 2.4Ghz
frequency as WiFi.

WiFi uses about 1/4 of a Watt, a typical microwave about 850 Watts,
there will be a a small amount of leakage from the microwave that's
not enough to worry about, but which will destroy the WiFi signal,
especially as it sounds like your Roku box is closer to the
microwave than to the computer (or WiFi access point if you have
one).

From
http://www.ofcom.org.uk/static/archi...rchive/rtl458/
rtl458.pdf

"2.0 Summary 2.1 The frequency measured from the domestic microwave
cookers varied between approximately 1.87GHz and 2.93GHz (1060MHz).
2.2 Between 2.0GHz and 2.75GHz (750MHz) the RF signal emanating from
the cooking chamber was approximately 10dB above the noise with the
major signal peaks at between 2.4GHz and 2.5GHz (100MHz). 2.3 The RF
power leaking from the all the domestic microwave cookers tested
varied between 1549mW and 245mW which is a difference of 8dB. 2.4
Leakage from the doors of domestic microwave cookers is greater from
cookers that at have been in constant use over a number of years."

Just checking my dodgy maths - is that between 1.59W and 0.245W?

Yes as near as makes no difference..

I am surprised by that as I thought the legal limit for safety reasons was
something like 1 or 10 mW per square cm anywhere near the device. Plus I'd
expect allowing radiation at the level of 1W would be unacceptable for
various interference reasons. Does the original mean 'milliwatts' or might
this be a case where 'm' has ended up being used for 'micro'?

Above said, whenever I power up my new laptop it tells me wifi is
available. Since I don't use wifi I guess it is picking up something from
another house. I'll see if our microwave affects that! :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , David WE Roberts
wrote:

From
http://www.ofcom.org.uk/static/archi...458/rtl458.pdf

I've now had a look at the above and am underwhelmed by the level of
detail, etc. My initial reaction was that if an undergrad had given me
this as a report I would have discussed it with them and sent them back to
the lab to do it properly! :-)

I've looked a few times at the report, and I may have missed something,
but at present my comments are...

Distance between source and measurement antenna not specified. (Yes this
matters unless we know the distance was great enough to put the source
antenna in each case and the measurement antenna into their respective 'far
fields' - which could be some distance for the microwave oven as an
antenna.)

Which antenna was used for measurements and which as the "substitution
antenna"? Can't see this in the report. (Yes it matters for the above
reason. A 20dB horn will have a longer far field than a lower gain
antenna.)

Measured power was in peak direction. Not an integrated result. No
indication of the integrated values for the actual microwave ovens.

Antenna patterns of antennas not given. This matters as a result of the
other points I make since the measurements seem to compare a peak directed
coupling (with unknown patterns) with the assumed behaviour of another
"substitution antenna" of unknown pattern and with values where it isn't
clear if they are either 'ERP' or real power totals or directed couplings.

Table at top of page 8 (section 5.3) has two columns for powers which I
will refer to as A and B via.

A = "Measured Peak erp (dBm)" and

B = "Max Radiated power (mW)"

but the use of neither of these terms is defined in the report so far as I
saw.

A is in dBm and the largest value is 0.0 (dBm) - i.e. 1 mW

Yet B for the same cooker is listed as 1549 mW - i.e. 31.9 dBm

The ratio between A and B seems to vary from one cooker to another, but
does tend to be of the order of 30dB.

Now if A *were* an ERP then it is hard to know what B means unless we
assume something like the "substitution antenna" had an apallingly low
radiation efficiency and had to driven by around 1 Watt in order to
radiate a total of 1mW!

An alternative possibility is that the report's author does not know the
meaning of ERP. :-)

I have a feeling that A was actually the nominal recieved levels at the
measurement instruments and B was the power poked into the "substitution
antenna" to get the same measured levels. But without knowing the patterns
distances, etc, this result is virtually meaningless if this is the case
since we are comparing two different radiated powers and couplings using a
rx level in one case and a tx level in the other - without even knowing
if the results *are* under mututal far field conditions.

OTOH we could imagine all kinds of alternative meanings for the powers
listed in the table.

We aren't told any of the settings on the measurement kit, either. This
also matters.

Conclusion: I have no idea if these results mean much. The A values may
seem consistent with powers/cmsquared of the order of less than a mW/sqcm.
But given the absence of any real explanations in the report even this is
guesswork.

Hence I have no idea if any of the ovens radiated powers above a 1mW let
alone a watt. The results don't really give enough info to tell.

Anyone have any *reliable* measurements on this?

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

An alternative possibility is that the report's author does not know the
meaning of ERP. :-)

I have a feeling that A was actually the nominal recieved levels at the
measurement instruments and B was the power poked into the "substitution
antenna" to get the same measured levels. But without knowing the patterns
distances, etc, this result is virtually meaningless if this is the case
since we are comparing two different radiated powers and couplings using a
rx level in one case and a tx level in the other - without even knowing
if the results *are* under mututal far field conditions.

OTOH we could imagine all kinds of alternative meanings for the powers
listed in the table.

We aren't told any of the settings on the measurement kit, either. This
also matters.

Conclusion: I have no idea if these results mean much. The A values may
seem consistent with powers/cmsquared of the order of less than a mW/sqcm.
But given the absence of any real explanations in the report even this is
guesswork.

Hence I have no idea if any of the ovens radiated powers above a 1mW let
alone a watt. The results don't really give enough info to tell.

Anyone have any *reliable* measurements on this?

Slainte,

Jim

Why don't you take it up with Ofcom Jim?.

And see what they have to say about their measurements?....
--
Tony Sayer

In article , tony sayer

wrote:
An alternative possibility is that the report's author does not know
the meaning of ERP. :-)
[snip]

Anyone have any *reliable* measurements on this?

Why don't you take it up with Ofcom Jim?.

Ars Long Vita Brevis. :-)

....or as I translate that, Life is too short to worry about past
politefoul/polite-ups. ;- Enough for now to caution that the
'results' presented in the reference may not mean what they seem to say.

I'll now go and find my 'Nice' albums to check the spelling...

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

The message
from Jim Lesurf contains these words:

In article , tony sayer

wrote:
An alternative possibility is that the report's author does not know
the meaning of ERP. :-)
[snip]

Anyone have any *reliable* measurements on this?

Why don't you take it up with Ofcom Jim?.

Ars Long Vita Brevis. :-)

....or as I translate that, Life is too short to worry about past
politefoul/polite-ups. ;- Enough for now to caution that the
'results' presented in the reference may not mean what they seem to say.

I'll now go and find my 'Nice' albums to check the spelling...

"Ars Longa Vita Brevis" afaicr. ;-)

In article , Jim Lesurf
writes
In article , David WE Roberts
wrote:

From

http://www.ofcom.org.uk/static/archi.../topics/archiv
e/rtl458/rtl458.pdf

I've now had a look at the above and am underwhelmed by the level of
detail, etc.
Bugger the detail Jim! How long will a 5-lb chicken take on an N+
router?

There's a war on, and every saving helps! ;-)
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)