Yes, a sense of perspective and proportions always helps.
A lot of current amateur gear show quite atrocious adjacent channel
performance,
especially in the hands of the "all knobs to the right" crowd.
I am currently engaged as a consultant in an HF transmitter procurement project
for air/ground services,
where adjacent channel performance actually is taken seriously.
Here the "specmanship" in terms of power output
and distortion levels from certain manufacturers really shows off.
It shows without doubt that in order to have "clean" signals, you have
to specify carefully, pay a lot, and finally operate your gear within
specifications.
I have read the works of K9YC, and he is cited in the paper,
"Performance Limitations For HF Communications Systems Using Realisable
Hardware Solutions"
that SM5HP and I wrote for the Nordic HF Conference in 2019 about how the
improvements in receiver technology have essentially become "nullified" by the
worsening transmitter adjacent channel emissions.
It is no real "point" in marketing receivers boasting 110 dB close-in dynamic
ranges, when current transmitters are
in the -30 to -50 dB range in the first and second adjacent channels.
73/
Karl-Arne
SM0AOM
----Ursprungligt meddelande----
Från : jim@audiosystemsgroup.com
Datum : 2021-05-26 - 11:15 (CEST)
Till : amps@contesting.com
Ämne : Re: [Amps] 300Hz sidebands
On 5/26/2021 1:31 AM, Conrad PA5Y wrote:
> As Bob AH7I pointed out at 1KW out the sidebands are 10mW, so I will continue
> to use the amp
Conrad,
As an engineer, I LOVE your proper sense of perspective. Here in the
former colonies, I often see splatter 0n 40M, most of it produced by
Yeasu rigs, that extends 2-3 kHz on both sides of the intentional
bandwidth, and only 20 dB down. That's 10W from a 1kW transmitter, and
the signal is 3 times wider than a clean SSB signal.
Any ham who transmits SSB with one of these atrocities is violating the
FCC regs on bandwidth that specify (and I'm paraphrasing here) that
occupied bandwidth shall be no greater than that required for the means
of transmission. In other words, if you're splatting wider than an
un-distorted SSB signal, you are in violation.
For years, I've had the P3 spectrum display with SVGA option hooked up
to my Elecraft K3, and I occasionally watch roundtable SSB QSOs.
Typically one or two stations will be textbook clean, while others will
have that splatter than I've described. And it's not subtle -- the
difference jumps out at you. Obviously the same problems can be caused
by poor or poorly operated power amps, but IMO, they're getting blamed
for a lot of problems caused by these lousy rigs!
73, Jim K9YC
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