By clean I mean - can I hear anything of
sufficient magnitude to disturb the noise floor anywhere in
band, and hence inhibit my ability to receive signals close to
the noise floor. The noise floor in a semi-rural location on
28, 50 and 70MHz is not particularly low so I do not feel that
this is unreasonable. The biggest problem with the IC7300 is
the AM noise bump at 20kHz and 130kHz which is only 60dB down
on the carrier when running at 30W on 28MHz. This power level
is typical when driving an amplifier. When modulated with an
SSB signal this occupies a considerable amount of bandwidth.
The close in PN -s only -120dBc/Hz at 1kHz and -130dBc/Hz at
10kHz. The composite noise is -115kHz at 10kHz, this is not
what I would consider clean, even close in. The K3S( and a few
others) is far better in this respect although the PA has
quite poor linearity, especially on 6m.
The Hermes will do a much better job with
any decent PA, even without pure signal. There are some spurs
@ -65dBc which improve with a higher sample rate. I have not
checked these with the V2 firmware but I will do immediately I
receive my Hermes from Apache.
I do not think that a transceiver at the
IC-7300 price point has fixed pre-distortion. As you quite
correctly say keeping it under control over temperature and
voltage variation would be difficult. Also Icom would almost
certainly have mentioned it in their advertising. What the
IC7300 does well is manage audio overshoots by using a ‘look
ahead’ algorithm. This is maybe where the impression of it
having a clean TX comes from.
I think that the problem here is that so
many transceivers are quite bad, so I can just about accept
that the IC-7300 is less bad.
73
Conrad PA5Y
OK, please refresh my mind what you mean by
"clean". It certainly appears to be sending something much
closer to pure signal concentrated within its intended
bandwidth than most other transmitters. I also understand that
it is not as good as it can be with full active predistortion.
Both might generate increased noise at some significant
separation from the intended signal frequency. I am not sure
of the mechanism by which this would take place.
As an ornery critter there is nothing I would sit down and
declare "clean" without a definition of "clean". I guess I am
asking for your definition of the term or even of the term
"clean enough".
{O.O}
On 20220225 01:13:11, Conrad, PA5Y wrote:
I KNOW for a fact that the IC7300 is not
clean. Please provide me some evidence to the contrary. I
have measurements with a R&S FSWP Signal analyser out to
a 1MHz BW. You guys are looking in an SSB BW which is fine
unless you happen to be 130kHz away, then you will hear
plenty of splatter from the IC7300. I tested the IC-7300 as
a result of hearing this on 50MHz. In other words the lab
tests were driven by on air experience.
You are spreading misleading and
incorrect information.
73
Conrad PA5Y
On Wed, Feb 23, 2022 at 12:24 PM, Max
wrote:
I just think if we follow good design
and signal chain management that superb, clean signals can
also be generated without the need for PS, that's all.
Max,
I disagree. My signal is my signature. Audio clarity is
admittedly important but what matters most to me is a
splatter-free signal, and in that regard nothing comes close
to what PS can produce. As I stated earlier, even the best
Class A amplifiers only have -40dB splatter. PS starts at -60db and often pushes
-70dB. That means that PS reduces splatter to less than 1%
(and at times only 1/10 of 1%) of what even the best
traditional equipment can produce.
I also agree with Simon that the 7300 (and also the 7610 for
that matter) produces an extremely sharp-edged signal with
unarguably less splatter than is achievable with any other
non-ANAN radio. It was explained to me by Ray N5LAX that the
reason those radios are so clean splatter-wise is because
ICOM embedded an algorithm into the firmware that functions
very similarly to PS in the sense that it corrects for
non-linearity in the PA, but it is a fixed-value (i.e.,
static) correction only, not a real-time self-adjusting
correction value such as is employed by PS. NOTE: I have not
been able to verify that info, but that is what was told to
me over-the-air by Ray when I commented that I had no idea
how the 7300 could produce such a clean, sharp-edged signal.
So I'm repeating it here.
IMO it's unwise and short-sighted to summarily dismiss the
game-changing value that PS brings to the hobby. Its
benefits are so unarguable that I (and Rob Sherwood) often
wonder why the big-name radios don't offer it as a standard
feature. It's free, so utilize it for goodness sake!
73,
Mark
