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Defeating AGC? - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


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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