Custom Search
Over 9,000 pages indexed!
|
| Your Host |
 KirtBlattenberger ... single-handedly redefining what an engineering website should be.
5CCG (5th
MOB): |
|
Hobby & Fun Airplanes and Rockets: Equine Kingdom: Doggy Dynasty: |
| ||||||
| ||||||
| AGC to which stages? - Comments welcome - 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. Charl Post subject: AGC to which stages? Posted: Mon Aug 21, 2006 7:58 am Colonel Joined: Fri May 19, 2006 5:01 am Posts: 25 Location: Netherlands Hello all, Looking at old schematics of tube radios, the AGC is usually wired to all stages: RF preamp, RF mixer, and IF stages (sometimes just the IF stages). Would I be able to get away with hooking it to just the RF preamp - possibly (DC) amplfied? I presume they used to connect the AGC to all stages to get more negative feedback out of a low voltage swing: -1V on one grid only brings gain down by so many dB, but -1V on 4 grids brings it down by much more. Thanks in advance, Charl Top languer Post subject: Posted: Mon Aug 21, 2006 3:39 pm Captain Joined: Sun May 14, 2006 8:53 pm Posts: 17 Location: Earth Do you have a particular application in mind? AGC is mainly there to keep everything linear, so if the first thing to non-linear is the RF-amp that's where you need it the most. Usually though the first thing is the IF. And because sometimes you have strong unwanted signals within your passband, you may want to start introducing loss (i.e. AGCing) in the IF so as to not affect your NF (and thus not heavily impacting a low-power desired signal). As I said before, it depends in your application. Top fred47 Post subject: AGCPosted: Mon Aug 28, 2006 11:11 pm General Joined: Wed Feb 22, 2006 3:51 pm Posts: 104 Hi! Just a quick note - it's actually very hard to design an amplifier with a gain that's variable over a wide range. That's why many circuits apply AGC to several stages - to get a wider control range. However, there are other considerations: intermodulation and noise figure, for example. That leads designers to use "delayed AGC", where some stages receive the AGC at levels that other stages don't receive it at. There are different nonlinearities used to get this, some not very visible. Good Luck! Fred Top Charl Post subject: Posted: Tue Aug 29, 2006 12:01 pm Colonel Joined: Fri May 19, 2006 5:01 am Posts: 25 Location: Netherlands Thanks fred, that's very helpful. Confirms my suspicions! :) Posted 11/12/2012 | ||||||
| ||||||
|
Please Support My Advertisers
|