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Icom IC-718 on AM

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Author Topic: Icom IC-718 on AM  (Read 29636 times)
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« on: October 25, 2005, 01:07:37 PM »

This inexpensive transceiver works at a rated 40W output on AM.   The audio compressor must be turned off. Back off the mike audio gain to about 50%.   While transmitting, set to monitor the output power.  If the power drops out on audio peaks, back off from the mike or lower the audio mike gain until it does not drop.   This is the setting that the ALC will not cut in.  You can also monitor the ALC while adjusting the mike gain until it does not change on audio peaks. 
« Reply #1 on: September 12, 2007, 05:54:09 AM »

You can also turn the modulation pot all the way up in radio, with that COMPRESSOR on, Mic Gain 4% and power level 50%(20 watts) to 60% (25 watts) for some great sounding audio, I was really surprised listening on another radio... It's certainly not plate modulated or sounds as good as my modified Yaesu FT-101EE BUT will certainly get you by in fine fashion and in a pinch for casual AM.

The compressor run like this cleans up the audio, makes the words a bit sharper and more articulate, and for some reason presents a louder audio on the receiver with ZILCH ALC clipping... Unless you start hollering into the Mic of 'course.

I used the stock hand mic for the test, and it worked great for me.
« Reply #2 on: September 12, 2007, 07:38:38 AM »

I did give another listen on a good receiver... With the compressor off a little more lows/bass in the audio and leans more toward a good clean sound, much like were used to listening on the bands..

The compressor tightens up the audio a bit.. More of a cut-thru-the-mustard sound. They both sound good though and have their place.

I noticed that by cranking the Mod pot up it dropped the alc level on the meter and seem to give the Icom a bit more "headroom" before she would buck the alc.. kinda hard to explain, but it works better all the way around with the mod Pot cranked wide open and the Mic gain at 4% with compressor on, and about 15% with compressor off, you might get away with 20% but at that point I detect a 'bit of distortion, something that may or may not be heard out in radio land.

Just my .02 cents... And that ain't worth much in this day and age!!  Grin

Pete, WA2CWA

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« Reply #3 on: September 12, 2007, 09:10:54 PM »

The IC-718 has an ACC jack on the rear panel. Pin 11 is modulator input. It bypasses all the front end audio "screwing around" circuitry, and provides a nice 10K input impedance for an "IHY" box or some some other audio tailoring type boxes. The input will work in SSB and AM modes and will typically lower the low end response and add a tad to the high frequency response. Note, with this connection, compressor becomes non-functioning and also front panel mike gain since they are both ahead of the pin 11 "modulator input". Sound better with no internal diddling with pots and 718 front panel controls. If you use the ACC connection, there is no need to connect the front panel mike. You can also key the rig from one of the pin connections on the ACC jack. A foot switch works great here.

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"

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« Reply #4 on: December 09, 2007, 10:34:52 AM »

I run my 718 at about 25-30 watts, modulation pot the whole way up, compressor on , and mic gain at 10. I gotten some good reports on the audio.

Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
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« Reply #5 on: December 10, 2007, 09:38:39 AM »

Still .... it would be nice to totally defeat the transmit ALC.  Turn it off. Pull the ALC rectifier or something like that.
Someone must have a schematic of this thing.

Ohh... the ALC still causes problems even when using the ACC audio input.
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