AGC on an ic-r75

lewg26 · #1 (**permalink**) 04-08-2009, 01:36 PM

I am using an IC-r75 and I was listing to some utility stations today and notced that there was some interference that would spike from s1 to almost s5 on my meter. It would happen about once per second and it made it almost impossible for me to set my squelch level. I tried turning off all of the noise sources I could think of and that made no difference at all. However, when I set the AGC control to "off" the noise stopped. I also haven't heard any traffic on the station I was listening to either. What is the AGC used for and should it be turned off when listening to USB? I bought this receiver used and it didn't come with a manual so I'm a little lost here. Any help would be appreciated.

Bucko · #2 (**permalink**) 04-08-2009, 02:39 PM

AGC means Automatic gain control. It helps keep the gain/audio at a steady level, with it off it could get over baring (loud). I monitor mainly Utilities myself on my R75 and leave the AGC on. Visit this site and download a user manual..IC-R75 HF+50 MHz All mode Communcations Receiver - Features - Icom America

WisconsinRailfan · #3 (**permalink**) 04-08-2009, 03:26 PM

I would also recommend you join the R75 Yahoo! Group. In the file section, look for Phils R75 Cook Book. It's a great resource for setting up, and getting the most out of the R75.

lewg26 · #4 (**permalink**) 04-08-2009, 04:50 PM

I guess what I don't understand is why taking the AGC off whould eliminate the noise spikes I was receiving. Actually, with the AGC off the entire noise level was reduced. I don't know if it affected the signal level also because I didn't have enough time to listen for another transmission.

nickcarr · #5 (**permalink**) 04-08-2009, 10:11 PM

By turning AGC off, you are basically turning off the extra signal gain. The radio will "pump" the gain when a signal is weak and vice versa.

I was told it's best to use Slow AGC for SSB and Fast AGC for AM broadcast.

As far as noise, that is more dependent upon your antenna system. What kind of antenna are you using?

-Nick

ridgescan · #6 (**permalink**) 04-09-2009, 09:42 AM

Interesting-I don't get jack---- with the AGC off. At least in my case the AGC makes the radio, so much so that I frankly do not see why there even IS an "off" option.

woody_46 · #7 (**permalink**) 04-09-2009, 06:09 PM

Try adjusting the RF/SQL knob when the AGC is off.

Phil's cookbook explains it..