In a message dated 96-12-10 01:24:25 EST, KM1H Carl writes:
>This has been a issue since the first synthesized TX hit the band.
>Take a serious look at the TX waveform picture in QST....most all of our
>rigs have been pictured over the past 12 years or so....at least back to
>the TS930 era.
>
>Now, look at that picture of the transmitted composite phase noise.
>Next, look at those spikes on either side of the carrier. Yep, most
>Riceboxes have them and they are typicallly 1.5 to 5 KHz from the
>carrier. Some worse than others, some have multiple peaks. What you see
>is what you hear.
These was some discussion on cq-contest about operating zero beat or next to
the band edge. I'd like to point out again that under the FCC's rules, the
operator is required by law to correct the problem caused by *any level* of
spurious emission that causes interference via splatter, keyclicks or
spurious emissions. No level that causes a problem outside the accepted BW of
the mode used is legal.
>Those spurs meet FCC specs and are over 50dB down, most decent rigs are
>-80dB or better. But now define 50 to 80dB down from someone who is
>40-60dB over S9 on your meter. Never mind that the meter lies
>anyway....you will still hear that spur loud and clear from any LOUD
>station and even from the not so loud guy given the wide range of
>possibilities (all legal).
These spurious emission levels are legal only if they don't cause
interference. 97.307a, b and c covers this. Modulation byproducts can not
extend out of band.
The ARRL changed its' IMD measurement techniques when solid state radios came
into use. The real standard is dB below one tone of a two equal tone test,
the new "standard" used at HQ is against PEP, which makes the splatter and
IMD look six dB better than true standard test methods does.
Typical third and fifth order IMD is now only 25 dB or so below a single
tone, where with the better tube type rigs it was in the -30 dB or better
range. Of course using the "new standard" modern radios look the same as the
old deluxe tube rigs, but they aren't.
The trash from new rigs is from multiple sorces, in my 751A the spurs were
caused by the external receive antenna and a poorly designed PIN switch
allowing the rig to oscillate. Key clicks were due to the synthesizer's VCO
swooping into lock while the TX was on, and the transmitter power overshoot
is due to the slow ALC response time. TX splatter was caused by a crummy bias
circuit and sub-standard linearity driver transistors.
I just received a forwarded E-mail from Eimac written by a person who
measured a new ICOM at 350 watts of pulse at the leading edge of the
envelope on SSB and CW. The overshoot was so bad, the guy wasted 3CX800's in
a few months of operation.
Figure out the clicks, splatter, and damage to PA's that power overshoot like
that causes.
The simplest temporary cure for all of this is to work wider splits with DX,
keeping the nasty stuff away from the DX windows or weak signal stations.
Manufacturers need to pay more attention to design of simple things like T/R
and ALC circuits.
IMHO, the whole idea of eliminating clear frequency DX windows or mixing SSB
and CW is techno-idioticy unless we all build new clean rigs.
73 Tom
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