[hpsdr] ALEX

[Phil Harman]

Thanks for all the great feedback regarding Alex. We are now looking a 
making a prototype board so we can actually measure the IP3 etc of some of 
the potential filters we are considering.

Rather than a bank of Bandpass filters another alternative is a tracking 
filter. I think that the new FT9000 series uses one of these and also 
perhaps the IC7800.  Does anyone have one of these receivers and can see 
from the circuit diagram what is being used?

There is also an intersting filter used in the the PT-8000 ( 
http://www.hilberling.de/) - have a look at the photo of the preselector. It 
seems to be using a relay switched 5 bit variable inductor mated with  8 
relay switched fixed capacitors. Given the large size of the toroid used I 
would expect the IP3 to be quite good.  Not sure how this is configured, a 
series tuned circuit perhaps, but it would be an interesting solution since 
we could cover the SW bands as well. If anyone has experience or futher 
information on these type of preselectors then please pass it on.

73's Phil....VK6APH





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