On 7/5/2017 12:23 AM, Richard Lamont wrote:
> Thank you for your rigorous, quantified mathematical proof.
Good engineering is not about math proofs, it's about big picture
analysis of entire systems, understanding the limitations of each
element, and concentrating on those elements that optimize the entire
system.
>
> Clearly the JT65 transmitted harmonics I've seen, as received on my K3S,
> which blotted out the weak JT9 station I was trying to work at around
> -27, must have been a figment of my imagination.
I'm not suggesting that wasn't real, but simply that harmonic distortion
at AF is not the only cause of the problem. And questioning that
shifting the TX signal to a frequency where the harmonic is out of the
audio passband is the only solution.
Using a better audio interface and setting levels correctly can easily
get individual AF distortion products 60 dB below the the level of sine
wave modulation. In an earlier post, I noted that interfaces sold to
semi-pro audio users generally offer THD in the range of 0.5 - 0.1% and
that number is the root-sum-square combination of the individual
components. In that earlier post, I included a link that suggested
specific make/models suitable for this use, all below $100 US, and four
easy ways for users to set levels, depending on the available tools
(including ears).
You also seem to have missed my objection that WSJT-X forces the radio
into split mode, when I want to use the second RX (controlled by the 2nd
VFO) to SIMULTANEOUSLY monitor CW while I'm in RX mode with WSJT-X, AND
to quickly do and A/B exchange of VFOs to work a station I hear on CW,
then return to WSJT-X. I did that almost continuously during the big
opening we experienced here last Friday, and one of those times got me a
new grid (in a new state) 2,500 miles away.
There's another powerful way to prevent overload of your RX by your
neighbor -- out here in W6, neighbors try to TX on the same cycle as our
neighbors. No math proofs required.
73, Jim K9YC
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