Forum: GNU Radio IF frequency of RFX400

Announcement (2017-05-07): www.ruby-forum.com is now read-only since I unfortunately do not have the time to support and maintain the forum any more. Please see rubyonrails.org/community and ruby-lang.org/en/community for other Rails- und Ruby-related community platforms.
melanio (Guest)
on 2007-07-03 06:54
(Received via mailing list)
Hi,



TVRX IF frequency is fixed at 44MHz, But the RFX400 IF frequency is 3MHz
or
4MHz, so DDC is -3MHz or -4MHz.

What is the reason does not use the fixed IF frequency?

I think which is not fixed seems to be a bit complicated. I wonder why
different IF frequency is necessary such as 3or 4MHz.

Is it the constraint because of the hardware?



can some help me with this problem?

thanks in advance



Sang-won



--------------------------------------------------------------------------

Sang-Won Kim @Cognitive Radio Research Team



Tel  : +82-42-860-4850   Fax : +82-42-860-5199

email :  <mailto:removed_email_address@domain.invalid> 
removed_email_address@domain.invalid
Matt E. (Guest)
on 2007-07-12 00:58
(Received via mailing list)
melanio wrote:
> I think which is not fixed seems to be a bit complicated. I wonder why
> different IF frequency is necessary such as 3or 4MHz…
>
> Is it the constraint because of the hardware?
>
>
>

We normally offset the LO from the desired receive signal so that you
don't have the DC offset (and DC offset compensation) right in the
middle of your signal.  Typically we use 4 MHz for this offset, but you
can change it to whatever you like, including 0.  This is why you see
the DDC tuned to -4MHz when you are looking at a frequency which is a
multiple of 2 MHz.  The LO on the RFX400 is set to tune in 2 MHz steps,
so when you tune to an odd multiple of 1 MHz, you see the DDC at -3 MHz.

All of the above is controlled in the gr-usrp/src/db_flexrf.py file.
You can change any of it if you wish, but usually you don't need to.
Reasons you would want to change it include having strong interferers on
your image frequency.

Matt
This topic is locked and can not be replied to.