> This thread puzzled me as it seemed that Tom and Bob were
> vehemently agreeing with each other. Let me explain:
>
> a) What did Tom W8JI say when asked what was so bad about
> the SDR-1000?
> "It has essentially the same dynamic range regardless
> of tone spacing"
>
> b) What did Bob N4HY say when asked what was so great
> about the SDR-1000?
>
> "It has essentially the same dynamic range regardless
> of tone spacing"
It would be nice if we could and stick with facts.
1.) All mixers "make noise" and all mixers have some
non-linearity. In a perfect passive mixer (which there is no
such thing) loss alone sets noise floor. When we connect an
antenna, unless we have a terrible mixer or terrible
antenna, external noise and not IM or mixer noise determines
what we hear. If the mixer performance creates a problem in
what we hear.... it is a horrible mixer or a we have a major
problem elsewhere in the system.
2.) If we have a filter that sets bandwidth at 10Hz by any
reasonable standard of xx dB down, say six dB down, any CW
signal through the system is limited to a very long very
soft rise and fall time. Any noise pulse will "ping" the
filter making what sounds like a tone. While it is true a
sharp brick wall filter makes the pinging (and group delay
through the filter) worse, its an entirely unavoidable fact
that the incoming signal is always reshaped and softened by
selectivity.
3.) What is not noticeable or even perceived as an advantage
at one place under one condition can be a disadvantage at
another. This is true with everything from antennas to
preamps to radios to headphones.
4.) Defending agreed upon facts with long subjective
arguments is a waste of time. It's nice just to know how
things work.
For example there is another tale going around that multiple
phase controlled transmitters can be used to feed multiple
elements, one example given is a four square. Yet a 4
square, like any typical unidirectional array with multiple
reasonably close spaced elements, has each element
significantly coupled to the other through mutual coupling.
In my own four square the perfectly symmetrical element
impedances range from 6 -j0.2ohms to 39 +j53 ohms and this
moves around when I change directions. The power needed by
each element is different, ranging from 95 watts to 618
watts depending on which element we look at and what
direction I beam at the moment.
Why would I replace one amplifier running near capacity and
a few coils, capacitors, and transmission lines with four
amplifiers requiring up to 12 matching systems....with three
of the amplifiers being heavily underutilized...when I could
just use a $20 switch, use fewer cheaper components, and
have the same result? If we ran all four amps into one
feedpoint and then phased passively at the antenna, we could
run around 2500 watts with significantly less hardware cost
and the same pattern.
It's great to build really neat things, but at some time we
have to understand how they fit the real world and that they
will still never be all things to all people. We need to
know there is no perfect free lunch, but there is always an
imperfect more expensive one.
73 Tom
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