Hi to All,
I have just uploaded a new article at eham, regarding the above title. It may
be accessed at https://www.eham.net/article/51274
The utube videos should be available within the next 12 hours.
Updated info on the Omni NB modification.
During the night when the extremely strong broadcast stations filled the 40m
band above 7200Mhz in Europe, significant intermodulation products appeared in
the 40m band only, when activating the modified NB.
Further testing showed that increasing the new resistance value installed
between R5 – R9 to 3M3, instead of 2M, led to improvement of the IMD products
while maintaining a similar effectiveness of the NB.. Based on the above
observations, my revised recommendation is to install a 3M3 resistor. This will
decrease the potential at the base of Q1 to 0.25V.
Apparently the IMD products are produced from the IC1 acting as a "mixer" when
huge signals are present within the near by frequencies.
Any ideas or suggestions on improving the IMD performance when the NB is
activated are welcome.
73,
Marinos, sv9dru / ki4gin
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