[TowerTalk] perspective

Wed, 19 Jul 2000 22:10:01 -0700

Hi Yuri, 

What you are saying is completely baffling to me. If the 
ionosphere is non-linear as you say, it would cut off the 
parts of your signal where the envelope dropped below
the minimum required entry threshold. Were you changing 
your output power in 1dB increments with a calibrated 
attenuator when the reporting station saw 5dB change in 
your signal? Was the observing station using a calibrated 
attenuator to measure your signal? How did you control 
for other variables such as fading? 

I just don't understand how the ionosphere would know to 
pass a large signal into the duct and not a weaker signal? 
And if it somehow knows how to do this, how come it doesn't 
create intermodulation distortion of SSB signals as the RF 
envelope of the signal is modulated thru the "media threshold" 
at an audio rate? I mean if you start attenuating your
transmit signal, the shape of the wavefronts hitting wouldn't
change, only the amplitude of fields would change, but they 
would do so proportionally.

Please expound/explain - Thanks! 

Mike, W4EF........................................

----- Original Message ----- 
From: <wa4dou@juno.com>
To: <towertalk@contesting.com>
Sent: Wednesday, July 19, 2000 9:23 AM
Subject: Re: [TowerTalk] perspective

> 
> Amen Tom. 73 Roy WA4DOU
> ----------------------------------------
> 
> On Wed, 19 Jul 2000 20:14:57 -0400 "Tom Rauch" <w8ji@contesting.com>
> writes:
> > 
> > You can really tell the hot topics!
> > 
> > Ian G3SEK had the same basic suggestion as W4EF. That might 
> > be a useful test. Maybe I'll do that in a blind test during the ARRL 
> > 
> > 160. Or would there be a problem I missing? 
> > 
> > RE Yuri's post, 
> > I wrote:
> > > > When 
> > > >  receiving at HF, gain doesn't matter. The antenna pattern and 
> > the
> > > >  direction of unwanted and wanted signals is all that matters. 
> > > 
> > > Not true. It matters! 
> > > I had many instances when Razors were hearing stuff when others 
> > couldn't
> > > make a whisper out of signals. Clean pattern helps S/N and QRM, 
> > but if
> > > there ain't no signal brought by antenna, there ain't no amplifier 
> > that
> > > can amplify it.
> > 
> > If a system is not limited by external noise at HF, it is time to 
> > have 
> > a long hard look at what is wrong with the system. At HF every 
> > stem with any kind of antenna at all should be limited by external 
> > noise, not internal noise. Once the system is limited by external 
> > noise, gain is absolutely meaningless.
> > 
> > An antenna with enough loss referenced to a dipole might give you 
> > problems, but there won't be any S/N difference between 0dBd and 
> > 10 dBd gain when listening to a signal if the antennas have the 
> > same pattern. If the patterns are different, the antenna with the 
> > highest ratio of sensitivity in the desired direction to power 
> > received 
> > from noise sources will win.  
> > 
> > > One more monkey wrench into philosophy that paths are reciprocal 
> > and can
> > > be nicely calculated (N6BT touches up on it in July QST p. 48): 1 
> > or 3 dB
> > > can make a difference in getting the signal into the layer or duct 
> > and
> > > propagating it. Sometimes 1 dB can demonstrate itself as 5 or more 
> > dB at
> > > the other end. It ain't exactly linear. (I know about RX S-meters 
> > being
> > > all over.)
> > 
> > If the ionosphere isn't linear, we are in for big time trouble. That 
> > 
> > means we have a mixer in the sky, mixing all the signals into sums 
> > and differences and harmonics there of.
> > 
> > We all know that isn't true, so it stands to reason the ionosphere 
> > is 
> > amplitude linear. 
> > 
> > > Those with stacks try switching them and compare results on RX and 
> > TX. You
> > > might be surprised how much difference there is between RX and TX 
> > signal
> > > reports, I found more like 60% disagreement.
> >  
> > I think you are saying the path isn't reciprocal. I'm sure that 
> > happens to a limited extent, in particular on low frequencies where 
> > the wave might be bent or rotated to slightly different paths. That 
> > isn't meaningful in justifying "free gain", because it would have to 
> > 
> > be a random event. In other words part of the time it would improve 
> > the reception more than transmission, and part of the time the 
> > other way around. Being random (and small), it would average out. 
> > 
> > We'd never be able to define that effect unless we all had perfectly 
> > 
> > calibrated meters at each end, no QSB, or did some very fast back 
> > and forth data exchanges and recorded the levels.
> > 
> > 
> >   
> > 73, Tom W8JI
> > w8ji@contesting.com
> > 
> > --
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> > 
> 
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