Envelope-to: dave@picks.force9.co.uk
Delivery-date: Wed, 01 Feb 2006 16:12:07 +0000
Message-ID: <001501c6274a$04bb8860$67b0fea9@lark>
From: "Alan Melia" <alan.melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
References: <000e01c6273f$7b8710f0$018cf8d4@standalone>
Date: Wed, 1 Feb 2006 16:09:53 -0000
MIME-Version: 1.0
Subject: LF: Re: Can't see the wood for the trees
Content-Type: text/plain; charset=Windows-1252; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Hi Andy I think what you are looking for is given on page 22 of my copy of
"Radio Engineers Handbook" by Terman I am sure you have access to a copy if
not I could scan

Cheers de Alan G3NYK

----- Original Message -----
From: Andy <actalbot@southsurf.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: 01 February 2006 14:51
Subject: LF: Can't see the wood for the trees


> Can someone help with what should be obvious.
>
> I have a train of constant width pulses at a fixed repetition rate.   In
the
> frequency domain these appear as a spectral comb with spacing at the
> repetition rate, whose amplitude  follows a SIN(X) / X shape depending on
> the pulse width, ie. the first null occuring at at 1/width and so on.
>
> What I'm getting tied up in knots trying to calculate is :
>
> What is the absolute amplitude (power) of just one individual tooth of the
> comb at any particular spacing.
>
> Assume the pulse waveform has, say,  1mW or 0dBm mean amplitude, and
> consists of 500us pulses at 40Hz PRI.   The duty cycle is 0.02, so the
> individual pulse power would have to be 50mW or 17dBm to get this mean.
> But what is the amplitude of the component at, say, 1kHz, or 1040Hz, or
> 10kHz ??
>
> It must be obvious, but I keep feeling the urge to integrate SIN(X) / X
> which is not funny and way beyond my maths capabilities!!
>
> The figures given above are those for the 5MHz beacon sounder sequence.
> The amplitude trace on the monitoring software during the sounder sequence
> is measuring just one line of the comb ( F = 0,  the carrier) , and
appears
> to suggest this is about 30 - 35dB down on the CW part.  That is -17dB
from
> the peak/mean  as above, but where does the other 13 - 18dB come from?
>
> Tearing hair out
>
> Andy  G4JNT
> www.scrbg.org/g4jnt/
>
>
>