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Testing group delay - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


 Post subject: Testing group delay
Posted: Tue Oct 16, 2007 1:26 am 
 
Captain
User avatar

Joined: Fri Jan 26, 2007 2:40 am
Posts: 23
Hello

I've got a superhet radio that has a group delay spec. We need to test this and I'm a bit confounded on how to do so.

Let's say that the input is at 30 MHz, it first gets up converted to 70 MHz IF (all the selectivity is done here) then is down converted to 50 kHz or so. Now, how does one test the group delay for this? What if you just wanted to test the time delay. How would that be done?

Thanks

jom


 
   
 
 Post subject:
Posted: Mon Oct 29, 2007 2:13 pm 
 
Captain
User avatar

Joined: Fri Jan 26, 2007 2:40 am
Posts: 23
OK, I'm not getting any response. This seems like a difficult task.

I'll simplify. How would one test a receiver noise figure which has an input of 30MHz and output at 50kHz? I think the frequency translation is the difficult part here so how is this normally tested? Whether it's NF or group delay or ripple or anything else it seems that testing under frequency translation is difficult.

Any ideas?

Thanks

jom


 
   
 
 Post subject:
Posted: Tue Oct 30, 2007 5:26 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 268
Location: London UK
Hi jom
Replying to the first point, frequency conversion does pose a problem.
Anritsu address the issue in a test procedure note on the site below:
http://www.us.anritsu.com/downloads/fil ... -00236.pdf
http://www.us.anritsu.com/downloads/files/11410-00236.pdf


Hope it helps. I have only ever measured GD of filters where Fin = Fout, but perhaps Anritsu have the answer for you.






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