<div dir="ltr">Segue artigo original do Tom DF5JL, em inglês:<div><br></div><div><br></div><div><span style="font-family:arial,sans-serif;font-size:13px">A new digimode jumps within an amateur band in the choice of QRGs back</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">and forth, with a high risk of interference to other stations. The day</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">before yesterday José Ros (EA5HVK) has unveiled its new mode called</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">FHSS-CDMA</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">(</span><a href="http://rosmodem.wordpress.com/2014/05/16/new-digital-mode-fhss-mode/" target="_blank" style="font-family:arial,sans-serif;font-size:13px">http://rosmodem.wordpress.com/2014/05/16/new-digital-mode-fhss-mode/</a><span style="font-family:arial,sans-serif;font-size:13px">) -</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">as an implementation within the new version of his digital mode software</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">ROS. Now a video published yesterday by Andy, K3UK, which shows clearly</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">the immense levels of possible interference by FHSS.</span><br style="font-family:arial,sans-serif;font-size:13px"><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">In Andy's video (</span><a href="http://www.youtube.com/embed/s0HVLxIQ2oE?vq=hd1080" target="_blank" style="font-family:arial,sans-serif;font-size:13px">http://www.youtube.com/embed/s0HVLxIQ2oE?vq=hd1080</a><span style="font-family:arial,sans-serif;font-size:13px">)</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">FHSS starts its procedure at 14115.0kHz. But within about only a minute</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">the following frequencies (kHz) are used by the hopping procedure rapidly:</span><br style="font-family:arial,sans-serif;font-size:13px">
<br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">14115.0</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">14063.0</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">14156.5</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">14266.5</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">14344.5</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">14055.0</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">14160.0</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">14300.5</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">14324.0</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">14065.0</span><br style="font-family:arial,sans-serif;font-size:13px">
<br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">A channnel detection ("busy"?) is not visible, i.e. FHSS obviously</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">doesn't evaluate whether the frequencies are in use by other stations /</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">modes or not. It turns out once again that as shown with ROS the</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">developer José Ros still do not seem to care about band plans and best</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">practice on ham's bands.</span><br style="font-family:arial,sans-serif;font-size:13px">
<br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">In the U.S. the use of spread spectrum by amateur radio below 222 MHz is</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">not permitted (see </span><a href="http://www.tapr.org/ss_fcc.html" target="_blank" style="font-family:arial,sans-serif;font-size:13px">http://www.tapr.org/ss_fcc.html</a><span style="font-family:arial,sans-serif;font-size:13px">). And we may ask if</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">spread spectrum generally is really a digimode for amateur radio. The</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">FHSS-CDMA method has not been specified in public by José Alberto Nieto</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">Ros (EA5HVK). But even when publishing it seems not to be what we can</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">call "an open mode". Because the pseudo-random sequence of FHSS-CDMA is</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">not known (José Ros: "Every transmission uses a different CDMA code</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">randomly chosen") this appears as pseudo-randomly and has a function of</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">a cryptographic key.</span><br style="font-family:arial,sans-serif;font-size:13px"><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">Frequency-hopping spread spectrum (FHSS) is a method of transmitting</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">radio signals by rapidly switching a carrier among many frequency</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">channels, using a pseudorandom sequence known to both transmitter and</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">receiver. It is used as a multiple access method in the</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">frequency-hopping code division multiple access (FH-CDMA) scheme.</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">Frequency spreading is generally used in military communications</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">(MILCOM) as in the civilian sector. The second generation (GSM) and the</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">third generation of mobile telephony (UMTS ) also uses the frequency</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">spread contained in CDMA. The reasons lie in the advantages of the</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">spread spectrum method: Due to the spread obtained to a greater</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">robustness against narrow-band interference; on the other hand it gives</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">a certain protection against eavesdropping. A spread-spectrum signal may</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">simply appear as an increase in the background noise to a narrowband</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">receiver. An eavesdropper may have difficulty intercepting a</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">transmission in real time if the pseudorandom sequence is not known. It</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">can also be difficult to recognize that any transmission takes place</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">(important for MILCOM, counterproductive for ham radio use).</span><br style="font-family:arial,sans-serif;font-size:13px">
<br style="font-family:arial,sans-serif;font-size:13px"><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">Best 73, Tom DF5JL</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">HF Dept. DARC (GER)</span><br style="font-family:arial,sans-serif;font-size:13px"><span style="font-family:arial,sans-serif;font-size:13px">Section "Digimodes"</span><br style="font-family:arial,sans-serif;font-size:13px">
<div class="gmail_extra"><br></div></div><div class="gmail_extra"><br></div><div class="gmail_extra">73,</div><div class="gmail_extra">--</div><div class="gmail_extra">Sérgio Matias, ct1hmn</div></div>