[AMPS] 3/2 power law and Rich's very wide signal

[Fred Fliss]

Rich and others, collectively, wrote:

>>>This is precisely whan happens.   The first cycle out of the exciter can
>>>be anything up to the limit of the Final Unit.
>>
>>
>>Surely not in practice.

>This is what my oscilloscope indicates.

That is the mark of a very poorly adjusted exciter, Rich.  Just as the 3/2 
power law is, in fact, a law that physics will enforce regardless of our 
desires, so, too is the relationship between the time domain and the 
frequency domain.  That relationship has been variously set forth by the 
likes of Oliver Heaviside, Fourier, LaPlace, and many others who predate the 
3/2 power law by hundreds of years.

If your exciter really does produce a signal whose amplitude is full power 
at the first RF cycle, you will be generating key clicks that are extremely 
wide.  Far wider than the 100 or so kHz you are claiming was produced by a 
DAF amplifier.

A properly adjusted "cw" rig (I put "cw" in quotes because our on-off keying 
method is not scientifically cw, which would be a continuous carrier, or A0 
modulation), MUST shape the keying waveform to eliminate key clicks.  As 
Steve alludes, the effective bandwidth of the signal is roughly equivalent 
to 1/3*(rise time of the signal).  I emphasize the word "roughly", but it is 
within an order of magnitude.  If properly shaped, a 'morse' code signal has 
a bandwidth of about 1/5 the speed in words per minute.  If the rise time is 
too fast, key clicks will result - the cw equivalent of "rotten splatter".  
You can feed your oscilloscope's waveforms into any free version of SPICE, 
or, for that matter, any Excel-based FFT algorithm to see for yourself.

Rise times on the order of 100 microseconds to 500 microseconds are what 
I've measured in the past.

I believe an RF source CAN produce a full power waveform in the first RF 
cycle.  I just hope to not be on the band when it happens.  I remember when 
I first saw this in action.  I was listening about on 40 metres one day and 
heard a lot of clatter.  I was tuning about the high end of SSB, perhaps 
7.28 MHz, and wondered what the noise was.  On the fast AGC setting of my RX 
switch, the peaks were about S9.  I tuned lower to find the signal.  It was 
a local ham on about 7.040 calling CQ.  His main signal was only S9 + 15dB!  
I called him on the phone to see what he was using for a rig.  He'd recently 
installed "relay QSK".  He had a relay doing the TX/RX switching.  The 
timing was such that the relay was making AND breaking with RF actuated.  So 
it was a guarantee that his first RF cycle was full power and his waveform 
also was cut off with the same rapidness.  Unfortunately, I could hope his 
relay would wear out, but as he was running a mere 10 watts, I had no such 
hope.  I was a lad of only 20, and he an old timer of 60, so there was also 
no hope of convincing him otherwise.

Many of the reflectees have scopes.  Next time you think of it, see if you 
can gather a sample of your cw waveform.  Don't even try it with an 
oversampling digital scope.  You'll have to use a single-shot digitizing 
scope or an analog scope to get the true picture.

Cheerio,

Fred
______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com


--
FAQ on WWW:               http://www.contesting.com/ampsfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm