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<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-GB
style="mso-ansi-language: EN-GB"><FONT face=Arial>Hi Phil and
all,<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office"
/><o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-GB
style="mso-ansi-language: EN-GB"><FONT face=Arial>the preselector of the PT-8000
is a series tuned circuit from 1.8 to 30MHz. The main inductance is based on a
T-200 toroid. Researches have revealed that the IMD characteristics correlate
with the mass of the material and the transformation ratio used. The IP3 of this
preselector was measured with +50dBm. The series circuit is tuned through
software by 5 inductor taps (5 bit) and an 8 bit capacitor set. A noise
generator is used to tune and store all settings in a table. In order to
enhance the filter characteristics the circuit is operating at approximately 3
ohms – there are down- and up transformers at in- and output.
</FONT></SPAN><SPAN lang=EN-GB style="mso-ansi-language: EN-GB"><FONT
face=Arial>We should have in mind the design goal for this solution: Hans
Hilberling, DK7LG, wanted to get a preselector with approximately 20 to
30dB out of band suppression. 20dB will give you 60dB enhancement in IMD/IP3
figures. If we look for more suppression to avoid 2<SUP>nd</SUP> harmonic mixer
products especially with the analogue mixers (QSD) this might not be sufficient.
I am working with 7 LPF for the entire HF spectrum. A HPF for (BC)signals below
1.5Mhz might be added.<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-GB
style="mso-ansi-language: EN-GB"><FONT face=Arial><SPAN
style="mso-spacerun: yes"></SPAN></FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-GB
style="mso-ansi-language: EN-GB"><FONT face=Arial></FONT></SPAN> </P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-GB
style="mso-ansi-language: EN-GB"><FONT face=Arial>73s – Klaus,
DK7XL</FONT></SPAN><SPAN style="mso-ansi-language: DE"><o:p></o:p></SPAN></P>
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<P>> <BR>> Message: 1<BR>> Date: Sat, 10 Mar 2007 10:02:50 +0900<BR>> From: "Phil Harman" <<A href="mailto:pvharman@arach.net.au">mailto:pvharman@arach.net.au</A>><BR>> Subject: [hpsdr] ALEX<BR>> To: <<A href="mailto:hpsdr@hpsdr.org">mailto:hpsdr@hpsdr.org</A>><BR>> Message-ID: <<A href="mailto:014c01c762af$d358cec0$0201a8c0@phil">mailto:014c01c762af$d358cec0$0201a8c0@phil</A>><BR>> Content-Type: text/plain; format=flowed; charset="iso-8859-1";<BR>> reply-type=original<BR>> <BR>> Thanks for all the great feedback regarding Alex. We are now looking a <BR>> making a prototype board so we can actually measure the IP3 etc of some of <BR>> the potential filters we are considering.<BR>> <BR>> Rather than a bank of Bandpass filters another alternative is a tracking <BR>> filter. I think that the new FT9000 series uses one of these and also <BR>> perhaps the IC7800. Does anyone have one of these receivers and can see <BR>> from the circuit diagram what is being used?<BR>> <BR>> There is also an intersting filter used in the the PT-8000 ( <BR>> <a href="http://www.hilberling.de/)">http://www.hilberling.de/)</a> - have a look at the photo of the preselector. It <BR>> seems to be using a relay switched 5 bit variable inductor mated with 8 <BR>> relay switched fixed capacitors. Given the large size of the toroid used I <BR>> would expect the IP3 to be quite good. Not sure how this is configured, a <BR>> series tuned circuit perhaps, but it would be an interesting solution since <BR>> we could cover the SW bands as well. If anyone has experience or futher <BR>> information on these type of preselectors then please pass it on.<BR>> <BR>> 73's Phil....VK6APH<BR>> <BR></P></P></BODY></HTML>