[TowerTalk] perspective

[wa4dou@juno.com]

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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