[hpsdr] MDS and relatet architectures

[KA2WEU at aol.com]

Hi, all
 
 
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
 
73 de Ulrich. N1UL
 
 
 
In a message dated 8/14/2006 1:08:42 P.M. Eastern Daylight Time,  
k3bu at optonline.net writes:


To add to the picture of super front end: 
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. 
 
2. Use the bandpass filters. They could be shared with TX in the  transceiver 
arrangement, switchable/selectable when needed.
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. 
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. 
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.  
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. 
5. AGC continuously adjustable - time constant (attack, release) and  gain 
(DSP derived?).  
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. 
7. Wonderful world of I-Q processing and controlling the  above.   
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. 
Yuri Blanarovich, K3BU, VE3BMV





-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/attachments/20060814/73941838/attachment-0004.htm>