Re: Digital Photography On Aircraft Not Permitted on Take Off or Landing

Floyd L. Davidson wrote:
user@xxxxxxxxxxxxxx wrote:
I actually tested my Canon 30D with a spectrum analyzer
that goes up to 1.8 gHz.

So you have a relatively cheap spectrum analyzer, designed
to look at L-band down-converters.

No, top of the line in its day, which was the late 70s.


This was with a 1 foot wire as antenna on the analyzer,
3 MHz bandwidth, and most sensitive setting.

But *what* is its most sensitive setting? You aren't giving
the numbers that mean something.

With the camera 6 inches from the antenna, there was
a small amount of wideband noise around 230 MHz

You have to determine the "gain" (which in this case
will be negative) of your antenna at that frequency in
order to provide a "normalized" power value.

Its in the near field. It doesn't HAVE a "gain", which is a
far-field concept.


The "noise floor" is something you don't appear to
understand. It is a function of the quality of your
spectrum analyzer.


You don't know what I know.

If you don't tell what the actual power values were, and
don't tell us what the minimum level you can see with
your particular equipment (i.e., what level it's noise
floor is), then the statement that the level of 10 dB
above something we don't know is meaningless.

The spikes were about -115 dBW. The broadband stuff averaged about
-108 dBW over 150-250 MHZ, which adds up to about
-100 dBW total. That of course is picked up
by the (near field) antenna, which is of course effectively
a 1/4 wave dipole at roughly 200 MHz.



At four feet from the camera, at various orientations to
check for polarization effects, nothing at all was visible
on the analyzer.

Given your test setup, that hardly seems surprising.

At 30 kHz bandpass, at 4 feet, the strongest of the discrete
frequencies were still invisible.

But what is the minimum signal level that you can
detect?


At 30 kHZ bandpass, about -140 dBW. Johnson noise at 300K is
-159 dB, so the NF is about 19 dB, a rather crappy value,
but this thing was not intended for off-air use without a preamp.

I tried it with a proper 1/2 wave dipole at 1.4 gHz,
30 kHZ bandwidth, and it dropped below the noise at about
a foot, camera oriented for largest signal. This was one
of the strongest high frequency signals. I've got
a good preamp (0.5 dB NF, 20 dB gain) at about 550 MHz but its
useless as all it picks up is (mostly digital) TV stations, which is what it is for. There are no signals from the camera in that area that are not covered up by the TV signals.



I'm sure you will find these numbers useless and add
a few more ad hominem attacks, but here they are.

Doug McDonald
.

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