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defeating AGC? - 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.


dinofizz
Post subject: defeating AGC? Posted: Tue Apr 03, 2007 5:45 am

Lieutenant

Joined: Tue Apr 03, 2007 5:16 am
Posts: 2
Location: Johannesburg, South Africa
hello my name is dino. im an ee student who is doing a high frequency techniques course. we have been given an antenna design assignment. we are to use an ordinary fm radio to test our antenna. the aim is to design an antenna for a specific fm frequency, and provide a filter solution such that interference from neighbouring stations is minimised.

this is very much a "go out and explore the solution on your own" assignment with little direction from the lecturer. we have been given a hint which says "signal strength can quite easily be established by defeating the AGC which automatically kicks in on low signal strength, by introducing attenuators. At these frequencies ordinary carbon resistors should do."

how does attenuation of the signal overcome a problem with the AGC? why is the AGC a problem? i cant find much information on specifically defeating the AGC with resistors. im a bit stuck on this part. any clarification or help would be greatly appreciated.


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darcyrandall2004
Post subject: Posted: Tue Apr 03, 2007 7:08 am

Colonel


Joined: Tue Feb 27, 2007 6:16 am
Posts: 46
AGC stands for Automatic Gain Control. If you remove the AGC from an AM radio, then weak signals will be amplified to the same extent as strong signals.

The best antennae will then be indicated by producing the largest sound at the speaker of the AM radio for the chosen test frequency.

Perhaps this is what your lecturer was asking of you.


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dinofizz
Post subject: Posted: Tue Apr 03, 2007 7:45 am

Lieutenant

Joined: Tue Apr 03, 2007 5:16 am
Posts: 2
Location: Johannesburg, South Africa
darcyrandall2004 wrote:
The best antennae will then be indicated by producing the largest sound at the speaker of the AM radio for the chosen test frequency.


thanks that does explain things in simpler terms for me.







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