Re: [Discuss-gnuradio] AR5000 and downconversion

[Joseph DiVerdi]

>And the answer is... the 10.7 IF output has two modes.
>
>http://www.aoruk.com/pdf/5000m.pdf
>page 29
>
><quote>
>
>6-18 CONFIG - EXTERNAL I.F. output
>(SDU5000)
>The AR5000 is capable of providing a 10.7 MHz I.F. output
>suitably wide enough to drive the optional SDU5000
>spectrum display unit with a bandwidth of up to ± 5 MHz.
>The I.F. output is default to OFF so must be activated
>before the SDU5000 (or any other similar peripheral) may
>be used.
>
><snip>
>
>The SUB DIAL is used to select the required parameter from
>those available:
>
>1 I.F. taken from before the selective filtering (least
>selective) and suitable for use with the optional SDU5000
>spectrum display unit. Should this selection not be made,
>the SDU5000 will not display a spectrum trace.
>
>2 I.F. taken from after the selective filtering (most
>selective) and is not suitable for use with the optional
>SDU5000.
>
>OFF I.F. output deactivated (default)
></quote>

Well, it now has been well established that the 10.7MHz output can be 
configured for a 10MHz (+/-5MHz) state and the concerns raised about the wide 
band output have been dashed by actual engineering. Now the questions (at least 
in my mind) are "How?" and "Why?"

I'm guessing that the answer to how is with a pair of filters in tandem, one 
high pass (5MHz) and one low pass (15MHz) which are always in line and the 
narrower band pass filters which provide the tens and hundreds of kHz are added 
downstream.

I'll also venture a guess that the why is because the SDU5000 unit has its own 
set of narrower band pass filters which it uses or not, as it chooses.
--
Joseph A. DiVerdi, Ph.D., M.B.A.
http://xtrsystems.com/           970.980.5868 (voice)
PGP Key ID: 0xD50A9E33