Message-ID: <E17B272C4CA44C89A9FDC388B8F9B984@Hugh>
From: "Hugh_m0wye" <m0wye@radiouk.com>
To: <rsgb_lf_group@blacksheep.org>
References: <4C0505F3.23023.3198CFC@mike.dennison.ntlworld.com>,<1OJR3q-0nK4tk0@fwd09.t-online.de> <BF4A524700075746A6467658DFC7102C5106464F20@ICTS-S-EXC2-CA.luna.kuleuven.be> <81893174-4350-4FE1-8D70-4FF4EBB44BCE@leeds.ac.uk> <13C79C2C1C7C41FB801BC4911C404C52@Hugh> <57EF78DF-0EB3-4719-A5D4-57966E86C1BE@leeds.ac.uk>
Date: Tue, 1 Jun 2010 17:23:32 +0100
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Subject: Re: LF: QRO / QRP
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Thankyou Chris, and Simon,
It was kind of you to take time out of your marking schedule to calculate 
that.

If I was transmitting a signal I wouldn't consciously decide how often to 
transmit photons, but I assume from what you say that emitting one photon 
per cycle that is the lowest continuous wave that one could transmit, and 
that a less frequent transmission would become interrupted, or amplitude 
modulated, although the amplitude modulation can't be in the conventional 
sense because that would broaden the spectrum and I would have thought that 
a single photon must be a single frequency - i.e. no bandwidth.

If I had a 1 Watt transmitter and fed it into a 240dB attenuator the output 
would be less than 12.3x10^-24W. If this were fed into an antenna then some 
cycles would occur before a photon could be emitted, now I'm wondering what 
happens to the power while it's building up, because a photon ought to be 
phase-closed - i.e. the cycle should be complete. This quantisation must 
play havoc with the calculation of things like radiation resistance, because 
at time no radiation occurs at times. Me thinks some very strange things 
must happen at low power levels.

Hmmm, I also should be working ... !

73 and thanks once again.
Hugh M0WYE




----- Original Message ----- 
From: "Chris Trayner" <C.Trayner@leeds.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, June 01, 2010 4:05 PM
Subject: Re: LF: QRO / QRP


Hi Hugh,

Thanks for the question - it's an excuse not to settle down to the marking 
again ;-)

>  there is a lower
> level of QRP which cannot be received by ANY receiver, no matter how well
> endowed with antennas and low noise amplifiers - simply because it is less
> than 1 photon.
> I wonder how small it is ?

The energy of a photon is E = h f
where h is Planck's constant, 6.626 . 10^-34 Js
and f is frequency, Hz.
(Physicists call frequency nu, but that is harder to typeset than f.)

Thus the energy of a photon at 136kHz is about 9 . 10^-29 Joules.

To get a power in watts you have to decide how often you are going to emit 
those photons - you could emit one every few days and get an arbitrarily low 
power.
To get some figure, suppose we emit one every cycle, i.e. 136k of them per 
second.
Then the power is P = E / T (T the period of the cycle), i.e. P = E f
For 136kHz this gives a power of 1.23 . 10^-23 W, i.e. 12.3 . 10^-24, i.e 
12.3 pico-pico-watts.

If your transmitter was only one million-million-millionth of a percent 
efficient, you could power it off the dynamic microphone you spoke into.


Ho, hum, back to the real world of marking.
73, Chris G4OKW

-----------------------
Dr Chris Trayner
School of Electronic & Electrical Engineering,
The University of Leeds,
Leeds LS2 9JT, United Kingdom
Tel: +44 113 34 32053
Fax: +44 113 34 32032