[TenTec] Bavarian Contest Club / Orion Review

[Duane Grotophorst]

--- K3BU at aol.com wrote:

> But if there is a certain amount of
> internal noise without antenna, 
> then it will mask puny signals before they manage to
> "climb" over the noise, 
> that is the fact and no amount of DSP mumbo-jumbo
> will "s'plain" it. 

In reality a "no antenna" test by itself is really
rather pointless. What does it really tell you?
Nothing other than the overall noise that the radio
generates internally, but that by itself is pretty
meaningless because it doesn't take into account how
much gain there is distributed throughout the radio's
RF/IF/AF stages. A radio with more gain will generally
"sound" noisier. You can only draw meaningful
conclusions if you reference that noise level against
the overall gain through the radio. No ham radio gear
manufacturer that I'm aware of provides any data about
the overall gain of their receivers in the specs. So
we don't really have a way to draw any good
conclusions by the "no antenna" test alone.

And I cringe when someone says they leave antenna
connector either open or shorted, neither are anywhere
near 50 ohms, the impedance that the radio is
presumably designed for. So who knows what unrealistic
variables a improperly impedance matched "no antenna"
test introduces. The proper test method for this would
be to use a 50 ohm load on the RX input.

My Pegasus excels when doing the "no antenna" (50 ohm
terminated) test criteria, I can crank the volume wide
open and not be driven out of the room, in fact I can
leave it that way all day long without becoming
fatigued either. I can't do that with the IC-765 or
706 I also have, but does that really tell me anything
about the sensitivity of the Peg vs Icoms? No not at
all, because when I do A/B/C RX receive switching
tests between them there isn't any meaningful
differences between any of them in terms of absolute
sensitivity. This is consistent with the ARRL lab
reports that show all modern receivers having MDS
figures within few dB of each other. What I can say is
that the received signal AND noise is louder on the
Icoms. So is there really any difference in
sensitivity? 

What DSP mumbo jumbo? All that the recommended weak
signal AGC settings for the Orion are desingned to do
is not allow the natural background band noise to
cause any AGC action. With the majority of the AGC
function of the Orion being done in the DSP we can now
have more control over how it works by tweaking
software parameters. But in the end its the ANALOG
components ahead of the DSP that ultimately limits the
radio's overall performance. A DSP IF radio can only
be as good as the analog stages ahead of it, DSP
simply can't undo the damage done to the signal by
poorly designed analog circuitry that precedes it.

Duane
N9DG


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