Topband: Digital mode spurious issues

[Steven Raas]

Tom,

I would have to agree. Let me also add my personal experiences on 160m
JT65, were good, however, at the latter stages of me being QRV on the band,
I was very politely spoken to, and delightfully educated on such matters by
Les, KL7J , whom really gave me some great insight on a then and still new
band to me, for this I am ever grateful. We tried to contact on many
occasions a few years back on 160M JT-65, however the latter attempts were
lower in the band , 1807 ish or so if I recall. I was one of the many daily
160M  ops for quite some time, but after learning, & progressing, if I was
QRV on 160 at the moment, I would take it ( digital ops ) down the band. I
will also admit, that I was lured with the possibility ( at those times )
of my 1st trans-oceanic 160m QSO using JT65 ( or any mode ) , with my
experiences now, I would say that waiting for prop, and running 4 or 5 cw
q's was much easier for those 1st trans-oceanic q's. Not to mention that
the long deep fades that I had ( with very very limited antennas which are
frequently common with 160 digi mode ops ) would not be very beneficial for
JT65 ' long haul / high qsb qso's, however this is not always the case. I
can even say that to this day, I had yet to work any DX on 160m JT-65, cw
now, is a different story thankfully :)  There is also WSPR activity in
that area of the band if I recall ( that may have changed ) amongst a few
others. I think that progress could be made in getting the digi ops to qsy,
perhaps to the lower end of the band, I'll be honest tho, I think that the
hardest part would be getting the word out to the masses, however when
presented with facts, and honest concern with the forsight of keeping the
band active and everyone happy, my guess is that few would gripe.. but the
masses just want to make qso's like the rest of us, and would in time
oblige. I digress..have a great new year everyone & enjoy !

-Steve Raas
N2JDQ


On Mon, Dec 30, 2013 at 10:55 PM, Tom W8JI <w8ji at w8ji.com> wrote:

> Thanks everyone for the suggestions. I'm going to have to install some
> software to identify some of the signals.
>
>
>
>  I would think that IMD products in a high-level PA that is over-driven
>> beyond good linearity  limits could add some junk in the "undesired
>> sideband"? FWIW
>>
>>
> IMD **requires** two or more signals at once, and does not appear anything
> like sideband leakage. This was a single shifting tone, and the lower
> frequency signal went the opposite way but the same amount as the main
> signal with shifts. That is classic for inadequate sideband suppression.
>
> There are multiple problems with using SSB to transmit audio tones and
> "thinking" it is a pure digi mode.
>
> 1.) things like this do not show on almost all digi waterfalls because
> they are out of passband of the other fellows receiver.
>
> 2.) SSB carrier, noise, and opposite sideband suppression is limited by
> the radio quality
>
> 3.) output purity is also limited by audio input purity, which includes
> audio line issues
>
> 4.) most digi operators do not have the low noise antennas most DXers
> have, and cannot hear some fairly strong signals. They are often on
> digimodes because of that!
>
> 5.) radios have terrible SSB transmitter performance compared to even fair
> receivers, so the transmitters often set the adjacent channel interference
> levels
>
> Placing digimodes near weak signal areas is not very wise frequency
> planning, but there is nothing anyone can do about it.
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>