Posted by
Tony Fegan VE3QF on
Apr 01, 2009; 4:01am
URL: http://elecraft.85.s1.nabble.com/K3-Revolutionary-Noise-Reduction-tp2567008.html
K3 - Revolutionary Noise Reduction
It was announced today, by Professor Morsig at the Institute of
Ljubljana, that the K3 has been chosen to test a revolutionary new
approach to combating receiver noise and improving HF reception.
The basic principal behind this approach is the shifting in
frequency of noise by a few mHz (that's milli-hertz) away from the tuned
frequency. This in effect produces a hole in the noise spectrum where
weaker signals may be detected. The residual noise is directly
proportional to the bandwidth of the hole. Therefore, for wider signals,
such as SSB, a modified approach is required. The hole is moved
progressively over the required signals bandwidth and the signal is
sampled at each step and integrated to reproduce the original wideband
signal.
A second feature associated with this algorithm deals with
variations in propagation. We all know that propagation is largely
dependent on the solar flux. Propagation is changed due to the effects
of the solar wind. A little known fact is that the remnants of the solar
wind that reach the receive antenna modulates the noise. When the noise
is detected this modulation can be interpreted to give information about
the condition of the D, E and F layers. This can be used to produce a
real-time table of MUF and critical frequencies for each layer. At night
some kind of remote sensing with suitable location corrections has to be
used.
The third and more revolutionary feature, which depends heavily on
the previous features, involves the generation and use of virtual
transceivers or individual ionosphere layer repeaters. As an example we
will assume a distant CW signal is transmitted on 21.110Mhz and the MUF
is around 15.000Mhz. The signal will not be refracted to our receiving
station and most of it is lost in space. If we transmit a heterodyning
carrier pulse on 14.110MHz, which is below the MUF, then it will mix
with the transmitted signal and produce a weak signal pulse at 7.000MHz
which is reflected back to the receiving station. There is a time delay
between the sending of the pulse and receiving the return pulse. The
transmitted pulse length is made less than this delay so that the
7.000MHz return pulse may be received between transmit pulses. This
process is repeated and the received signals integrated to reconstitute
the original signal sent.
There are some operating problems to be worked out with the
transmission of multiple heterodyning carriers. Thus only a few K3's are
expected be loaded with the new firmware until these problems are
resolved (spread spectrum has been suggested).
New menu items may be added to include these features in a future
K3 DSP firmware update. MUF OFF/AUTO and 1-10 will vary the effect of
received signals using simulated MUF values. This can improve signals on
all bands. Unfortunately this enhancement is not reciprocal and only
works on receive. Thus K3 to K3 contacts should have a distinct
advantage. The algorithms used are not open source as these features are
expected to have a huge affect on the whole radio communications
industry. It is still in the early beta-test stages.
The above is a rough summary of the original unwinese language
document submitted by Professor G. E. T. Morsig who is the 1st Associate
Professor of Radio at the Institute of Ljubljana. He will be very
interested in your assessment of this system and may be contacted via
F(zero)OL (qrz.com).
My apologies if I have made a minor slip or two in the translation.
Unwinese is not an easy language to translate.
Please do not contact Elecraft for this firmware until there is an
official statement!
73 and Enjoy
Tony Fegan VE3QF (anxiously awaiting further developments!)
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