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Why do HF transceivers have such low level AM modulation?

My FTdx3000D sounds good on AM. What few times I have used it on 6 meters AM.
The really excellent one is my FT920 which is really good on AM. This one unannounced to me when I bought it had been Voo-dooized and modified with the 6 KC INRAD AM filter. (the 2.4 KC factory filter was removed and the INRAD installed)
On 75,10 and 6 meters, AM with about 25 watts carrier will do close to 125 watts with a Heil PR781 mic, on everyone's scope it is like 7 KC wide transmit!
I truly don't like it this way as on normal SSB it is like 4 KC wide even with the ALC set properly or below a normal level.
I plan on sending it out to a shop that does Yaesu work primarily and have all those JUNK mods removed!
I plan on keeping it as the dual receive and the great tone from the receiver I do really enjoy.
Just my 2 cents worth.
All the Best
Gary
 
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Shadetree Mechanic said:
I wonder if the accessory socket in the back would have some voltage to use instead of a battery? If using a battery it would be nice to have a switch to turn it off when not in use too. Would a wall wart be too noisy?
Click to expand...
You must use external source. Can be external power supply, but quality one, with current limiter and voltage adjust. No more 500k pot.
Could be built with LM317, but safe way is just to use battery.
Mike
 
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Transmitters that have good bandwidth and strong AM audio can also be the filthiest signals on the band when not properly adjusted and limited. As AM became less important on HF rigs, manufacturers took their low level IF modulation practices one step further. They all modulate a low level stage in front of the extremely restrictive crystal filter. That also makes it nearly impossible to cause splatter through that filter at the expense of audio quality.

The solution is NOT to bypass the filter since that can allow mixer byproducts to pass through the RF amplifier stages and make it on the air. You must remove the modulation prior to the IF filter and modulate a low level stage after the filter. This unlocks potential that you'll never see just messing around with ALC. Even on the FT-1000D, the improvement is dramatic. Using the radio modified like this will piss off others on the band if you do not add sharp high frequency roll off and peak limiting.
 
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Data jacks often have wider frequency response than the mic jack but this in not what I was referring to. In the case of rigs like the FT-1000D I was talking about abandoning the SSB balanced modulator altogether on AM in favor of applying the audio from the rigs mic pre amp chip directly to the power control FET. This provides conventional AM capabilities without the restrictions of the IF strip.

The best part about this mod is just about every rig I've tried it on, already has everything it needs inside to make "real" AM. It's just that they have decided to treat AM as nothing more than double sideband with the carrier balance offset. So far I've found that the TS-50S and the FT-857D were some of the few that actually required an additional AF stage built to modulate the needed RF stage. The trick is wiring the modification through a relay that only activates it on AM.
 
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Shockwave said:
Data jacks often have wider frequency response than the mic jack but this in not what I was referring to. In the case of rigs like the FT-1000D I was talking about abandoning the SSB balanced modulator altogether on AM in favor of applying the audio from the rigs mic pre amp chip directly to the power control FET. This provides conventional AM capabilities without the restrictions of the IF strip.

The best part about this mod is just about every rig I've tried it on, already has everything it needs inside to make "real" AM. It's just that they have decided to treat AM as nothing more than double sideband with the carrier balance offset. So far I've found that the TS-50S and the FT-857D were some of the few that actually required an additional AF stage built to modulate the needed RF stage. The trick is wiring the modification through a relay that only activates it on AM.
Click to expand...
I’m interested in details of this mod. I know majority of the newer rigs run the AM audio through a DSP and a balanced Modulator. Icom rigs I have both suffer from low modulation .
 
sp5it said:
Battery + to 1, - to 3
RCA tip to 2, sleeve to 1

View attachment 32684
Click to expand...
I tried this on my Icom IC 7300.
When transmitting a full 25-watt carrier I see about 60 watt pep on my bird 43p.
Why add this device to the ALC jack I don't notice any more pep output. When I turn the potentiometer too far one way the radios ALC meter pegs out and the radio has no output?
I double checked everything and it is wired correctly.
Unfortunately I could not achieve what I was hoping for.
 
Agree with all commented on above. I have personally found excellent AM audio on the original Icom 746 (NOT PRO) and their 706 Series mobiles sounded good on AM.
 
SMILEX, did you ever figure this out on the IC-7300? I tried the ALC potentiometer defeat on the IC-735 years ago and it worked like a champ, radio modulated like a Cobra 29 from any reasonable carrier setting below 25 watts. When I briefly tried it on an IC-7300 recently I did not observe the same desired effect. Too bad.
 
FredTx63 said:
SMILEX, did you ever figure this out on the IC-7300? I tried the ALC potentiometer defeat on the IC-735 years ago and it worked like a champ, radio modulated like a Cobra 29 from any reasonable carrier setting below 25 watts. When I briefly tried it on an IC-7300 recently I did not observe the same desired effect. Too bad.
Click to expand...
Fred, I have not tried anything else. I have pretty much given up on it with the IC7300
 

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