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<DIV>Hi, all</DIV>
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<DIV>IT GOES WITHOUTS SAYING that there needs to use a pre-selector. In my
case, XK2100L, we use a binary coded two stage approach, with 5 db input loss, 5
dB output loss, total 10dB loss, 1dB NF of the amp between the two tuned
circuits. They have 20dB attenuation in 10% offset, ie at 10 MHz center freq. 20
db down at 11MHz. This filter is used in RX and in TX mode (at 10mW level). This
avoids co-location problems...This system has a net NF of 6dB and an IP3 of 42
dBm</DIV>
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<DIV>73 de Ulrich. N1UL</DIV>
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<DIV>In a message dated 8/14/2006 1:08:42 P.M. Eastern Daylight Time,
k3bu@optonline.net writes:</DIV>
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<P>To add to the picture of super front end:</P>
<P>1. In case if there is a problem controlling the gain of RF preamp, the
step and programmable attenuator should be used on the front as outlined by
N1UL. </P>
<P>2. Use the bandpass filters. They could be shared with TX in the
transceiver arrangement, switchable/selectable when needed.<BR>This is
important in Multi-Multi station setup, where strong local signals (kW on the
next table/antenna) from other bands are source of overload.</P>
<P>3. Use of tunable band filters on the front and behind of RF preamp. Hi-Q
circuits or variation of Q multiplier/notch. Selectable if needed. <BR>They
are needed especially on low bands 40/80/160, when very strong signals within
the band are present and one is digging for weak ones in close proximity. </P>
<P>4. RF preamp switchable in/out. In case signal levels are sufficient (high
gain antennas) switch it out to improve IP3. Have items 1, 2, 3, available as
needed.</P>
<P>5. AGC continuously adjustable - time constant (attack, release) and
gain (DSP derived?). </P>
<P>6. High level mixer with clean injection signal followed by
selectable Xtal filters - steep skirted and/or low ringing banks. Option
to take the wide band or filtered bandwidth for bandscope/waterfall or
filtered signals.</P>
<P>7. Wonderful world of I-Q processing and controlling the
above. </P>
<P>Unless we have super overload mixer that can tolerate and eliminate the
above, the preamp and filtering use if needed is highly desirable and should
beat anything out there. Right now we have to use variations of outboard
gadgets. Incorporating them into the RX front end design and be able to
control switching and settings as needed by various antennas and situations
would make the ride ultimate and not available presently in any of the rigs
AFAIK.</P>
<P>Yuri Blanarovich, K3BU, VE3BMV<BR><BR></P></FONT></BLOCKQUOTE></DIV>
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