Hi Art
I'd say that every little bit helps when conditions are marginal. Even
10dB extra mean pretty well nothing in readability when the signal is
already 20dB above the noise, but a few dB *can* make a difference when
the signal is in noise.
I don't see that! would not the S/N stay the same?
Well to tell you the truth this was one of those "told by someone else"
things that I never did get around to proving myself (thinking it was
general knowledge) I have of course noticed it on 2M FM where the
recovered audio S/N falls off very rapidly as the usable senitivity of
the radio is reached. In that case a 1 or 2dB signal increase can make
the difference between readable 1 and readable 4. I have a funny feeling
the discussion I heard on the topic may have been on front end NF of
VHF/UHF receivers where a 1dB lower number there yielded a much larger
dB result. Note this was for SSB. I have some work to do here
understanding this. When I look at building another preamp for 2/70 I'll
do it then!
However if the noise is -110dBm and the signal was -114dBm, the margin
(s/n) would become less (of a negative number) when the signal level is
increased. You may not be able to resolve it but you can measure the
difference. You can of course use DSP techniques to resolve signals
weaker than noise. WRSS60 for example will enable you to resolve signals
26dB below the noise level. FSK441/JT44 is another example of signal
below noise reception.
For horizontal waves the ground conditions relative to 1 wavelength is of
little concern
Height as always helps with low TOA so one has to determine the average
incoming signal angle
of choice QSO's and design to suit.
Something about brewster angles and phase reversal in horizontal but not
vertical polarisation? (Note I work in IT, not RF!) I always thought
that the poorer the ground (eg sand/clay) the higher the takeoff angle
and over seawater was the lowest one could attain. (Keep in mind that VK
dropped CW earlier this year and I was one of those that has been
playing VHF+ for the last 25 years!)
Agreed but I would like to see smaller turning radius ( moving away
from the
boom length mantra , )
without the necessity for dual driven stacked array This would require a
fixed feed point with
moveable elements for desired TOA to suit desired QSO..
I would also expect that F/B & F/S are major contributors to design to.
Very handy when you neighbours son a few miles away wants to tune his VW
engine! I like the idea of a quad, simply because of its smaller turning
radius!
I once had a think about ways to tune a 3 element quad for best F/B.
Maybe some way to roll the wire up on a small motor shaft or tune it
with some C on the end of some tuned length feeder? Didnt figure out an
easy way to change the element spacing though. Maybe bending the
spreaders would have a similar effect of changing the feedpoint
positions on a stacked array?
You could also change the length of the phasing sections for a dual
driven stacked array - rather than moving the feedpoint. If I was
experimenting with this idea I'd probably start (modeling) with 3
parallel horizontal dipoles arranged such that when viewed from the ends
the (end point) shape was a triangle. All would be fed in parallel but
with different phase relationships between them.
I am sure it can be done, and since 'every thing is
known about antennas' all that is reguired is for a Guru to come forward to
share how it is done.
Not me sorry. If however I stumble onto something that defies all the
theory and works better than anyone else, this NG will be the first to
know - and I'll make the design like GPL software! Free...
Cheers Bob VK2YQA
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