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From: Jeff Liebermann on 4 Apr 2008 11:17
On Thu, 3 Apr 2008 16:13:32 -0700 (PDT), Adam Chapman
<adam.chapman(a)student.manchester.ac.uk> wrote:

>I read that the Cisco Aironet
>2.4 GHz Bridge transmitter power is 20 dBm. I cant seem to find a
>defintion for a bridge transmitter though, so im not sure if i know
>the Tx power of the patch antenna or not. Does 20 dBm seem reasonable
>for this antenna?

The power rating of an antenna is the point where the antenna can be
safely operated without melting, arcing, or self-destructing. There's
no way an antenna is going to do any of these at 20dBm (100
milliwatts).

>If the patch antenna power is 20dBm (which is the legal maximum in the
>UK), then over a 550m range the SOM should be just below 28 dB
>according to my calculations. Although I was aiming for 28 or above
>the PER does not appear to be too bad.

Antenna power handling ability has nothing to do with range.

Any antenna that has the proper gain, size, and weight characteristics
will work. It's up to you to determine the requirements.

--
Jeff Liebermann jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: Jeff Liebermann on 4 Apr 2008 11:29
On Thu, 03 Apr 2008 16:57:55 -0500, DTC <me(a)nothingtoseehere.zzx>
wrote:

>Jeff Liebermann wrote:
>> Radiosondes have two basic assumptions. The transmitter is always
>> above the receiver and that antenna is always roughly vertically
>> oriented.
>
>Not so. The weather reporting radiosonde used in the 60s and 70s
>aways drifted off to the horizon, driven by the prevailing wind.

Sure. Assuming a flat earth model, the tracking antenna cannot be
expected to dip much below horizontal. My point is that there was no
need for any RF to be radiated by the radiosonde ABOVE the horizon or
in an upwards direction. You can't make that assumption with a model
airplane, which can fly upside down, and does require RF to be
radiated in the upward direction.

>The radio receiver was something like a ten foot diameter dish
>under a plastic radome that tracked the radiosonde.

I have one in the closet somewhere. I'll dig it out and take some
photos (later). It's amazingly crude and cheaply made.

>As i recall, they had a single tube transmitter that was frequency
>modulated by the thermometer and air pressure was sensed by a
>bellows that was mechanically connected to a rheostat that pulse
>proportional modulated the signal. All this is going back over
>thirty years ago when I played with the project.

Tube? Thermionic Valve? Whazzat? Dis is da space age. We don't do
no stinkin tubes.

>Direction was resolved by the rotation coordinates of the dish.


--
Jeff Liebermann jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: msg on 4 Apr 2008 15:35
Jeff Liebermann wrote:

<snip>
>
> Tube? Thermionic Valve? Whazzat? Dis is da space age. We don't do
> no stinkin tubes.

Ground support computers for the first few Redstone/Mercury launches
included Bendix G-15 vacuum tube machines; most of the hardware
was in fact tube-based. IIRC, the Mercury capsule even contained
some tubes.

Michael


From: DTC on 4 Apr 2008 19:12
msg wrote:
> There was a baroswitch which selected the sensor to read based on
> increments in altitude; the modulation was PRR.

That's the phrase I was trying to remember, Pulse Repletion Rate.
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