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    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

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

Joined: Fri Jan 26, 2007 2:40 am

Posts: 23


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?



 Post subject:
Posted: Mon Oct 29, 2007 2:13 pm 
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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?



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


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

Posted  11/12/2012

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