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Re: Copy of: RE: Drake downconverters



Joe Steinmetz
kc6szy wrote:
>I am converting mine for operation at 2273 (with a preamp!). My LO is
>2000 MHz, my crystal is 7.813 MHz. I didn't have the 10pF cap. Do
>have any circuit data? I am locating a 10pF cap, but in the meantime,
>I was wondering if you knew the relationship of the cap (and i presume
>the resistor) to the LO crystal? Again, I am assuming that it is the
>cap that makes up some sort of loop filter for the PLL?

OK, using this thing at 2273 is going to be a problem. I have swept both
new and modified Drake 2880 and they simply die below about 2450 MHz. By
2400, they are at least 25 db down from what they are gain wise at 2500.
Very sharp bandpass skirts with -3db points atabout 2475 and 2700 MHz. When
you modify the IF (removing a high pass filter), the response improves on
the low end to where 2400 is only about 12 db down, but there is still 15db
gain in the converter, so it works. By 2300, you are over 25db down again
(the converter has ~27db gain). By 2270, there is less than nothing left.
What you can do is lengthen the bandpass filter legs about .04" to make it
"kinda OK" at 2270. 
Good Luck!

73,
Ed K9EK
AMSAT S-band nut






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