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Satellite PC Card Receivers, Internet by Satellite
neumoDVB
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<blockquote data-quote="deeptho" data-source="post: 1144374" data-attributes="member: 215446"><p>[USER=297935]@satesco[/USER] So that is what you mean. I could not have guessed.</p><p>Anyway: 12725.290 - 11175.22 = 1550.07 which almost exactly equals the local oscillator frequency of the stid135 chip</p><p></p><p>When tuning to the high band, what happens is that the very string 11175 comes into the card </p><p>at a frequency of 11175.22- 10600 = 575.22 Mhz (use tbs5927 or tbs603 to verify)</p><p></p><p>Internally the card tunes around the center frequency of 1550 with a bandwidth of about 1200 Mhz.</p><p>So between 950Mhz and 2150 Mhz. However, the bandpass filter is not perfect, and any incoming frequency </p><p>f below 950Mhz that is not sufficiently attenuated will also appear at f+1550 Mhz.</p><p></p><p></p><p>For f=575.22 Mhz, the aliased value equals 2125.25 Mhz</p><p></p><p>On the other hand, if a real signal appears at 12725.290H then the frequency received by the chip</p><p>equals 12725.29 - 10600 = 2125.29 Mhz, which is almost exactly the same</p><p></p><p></p><p>Also, if the LNB suppress signals outside its designed band, like 575.22 Mhz, then this problem would also not</p><p>exist. So you could also blame the lnb.</p><p></p><p>Try the following experiment: reduce the signal coming into the card using an attenuator, At some point the 12725.29</p><p>will disappear into the noise. You can of course also put a wet cloth on the lnb, which will also reduce the signal.</p><p></p><p>Other cards do not have this problem as they tune to a much narrowerd band (e.g., 60Mhz bandwidth instead of 1.2Ghz)</p></blockquote><p></p>
[QUOTE="deeptho, post: 1144374, member: 215446"] [USER=297935]@satesco[/USER] So that is what you mean. I could not have guessed. Anyway: 12725.290 - 11175.22 = 1550.07 which almost exactly equals the local oscillator frequency of the stid135 chip When tuning to the high band, what happens is that the very string 11175 comes into the card at a frequency of 11175.22- 10600 = 575.22 Mhz (use tbs5927 or tbs603 to verify) Internally the card tunes around the center frequency of 1550 with a bandwidth of about 1200 Mhz. So between 950Mhz and 2150 Mhz. However, the bandpass filter is not perfect, and any incoming frequency f below 950Mhz that is not sufficiently attenuated will also appear at f+1550 Mhz. For f=575.22 Mhz, the aliased value equals 2125.25 Mhz On the other hand, if a real signal appears at 12725.290H then the frequency received by the chip equals 12725.29 - 10600 = 2125.29 Mhz, which is almost exactly the same Also, if the LNB suppress signals outside its designed band, like 575.22 Mhz, then this problem would also not exist. So you could also blame the lnb. Try the following experiment: reduce the signal coming into the card using an attenuator, At some point the 12725.29 will disappear into the noise. You can of course also put a wet cloth on the lnb, which will also reduce the signal. Other cards do not have this problem as they tune to a much narrowerd band (e.g., 60Mhz bandwidth instead of 1.2Ghz) [/QUOTE]
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Satellite PC Card Receivers, Internet by Satellite
neumoDVB
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