[TowerTalk] perspective

[Tom Rauch]

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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