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Message |
    
Audioman
Junior Member
Username: Audioman
Post Number: 37
Registered: 2-2004
| | Posted on Friday, November 25, 2005 - 1:54 am: | 
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I have a brand new Yaesu T-840. I purchased the AM filter for and did the 11 meter mod. Works perfect. Air reports are that I sound studio quality. But I have a negative modulation swing. Sometimes I lose 2-3 S units when speaking. It does this with the stock mic or the Heil mic that I purchased. I know all about the ALC and how it's supposed to work and am within the metering range when I speak. It happens at any volume I set the gain at. This is my second 840 and they are both doing the same thing. Is there a way I can have this radio give me the forward modulation that should be there? I'm not after nor am I impressed with forward swing, but you should have some sort of forward modulation when you transmit with any radio. This seems to happen at any volume of the mic gain and any power setting of the radio. Is this normal for Ham equipment? Any help would be appreciated. Thank you. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1940
Registered: 7-2004
| | Posted on Friday, November 25, 2005 - 11:43 am: |
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adjust the 'rf carrier power' control down to a lower dead key. not the front rf power control, but there is probably another 1 on the back of the radio that may even need a small screwdriver/tuning tool to get to. then readjust as per manual.
my ic735 says to adjust it so it shows 40% on meter, but i find that still to be a bit too high. at about 30 watts(with front control at full power)it will show some upward swing on wattmeter. any more & it shows downward-a bit more before it shows downward swing to receiving stations, though. had it checked on scope a while back, there is a point where though it shows downward on wattmeter, it doesn't show it as such on scope. at that point, with shure 526t mic on it, AM audio is pretty good. i do get 'the S9 sounds louder, but the icom has more carrier' signal reports on AM. on SSB it is a SMOKIN' radio with that mic. several 840's here on LI on LSB38, most sound pretty good. on AM though they have trouble adjsuting 'em & 1 even sounds as though it is still on SSB... |
Bruce
Senior Member
Username: Bruce
Post Number: 3257
Registered: 9-2003
| | Posted on Friday, November 25, 2005 - 1:14 pm: |
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HUMMMMMM?
Your right on AM the 840 downward modulates.
You might contact Yaesu but my guess is they SUBTRACT the audio from the 25 watt carrer. |
Slugo4449
Member
Username: Slugo4449
Post Number: 60
Registered: 7-2004
| | Posted on Wednesday, November 30, 2005 - 12:19 am: |
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I have a question.
Does it do the same thing into a dummy load?
If it swings forward into a dummy load it may be the antenna or coaxial cable. Are you getting reverse swing on the radios meter or an external wattmeter?
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Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1978
Registered: 7-2004
| | Posted on Wednesday, November 30, 2005 - 3:15 pm: |
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MINE is on external wattmeter, radio meter shows forward. same into dummy load. bruce is probably correct. dropping RF CARRIER DOWN & LOWERING radio mic gain lessens the trouble, then a power mic with some gain, such as the shure 526t, brings audio output up. problem is seen as 'no problem' when viewed on a scope.
if you DON"T follow manufacturers directions, LOW deflection on ALC meter, etc, this will show on MOST HF rigs this way. lots of meter swing on HF rig is NOT how most were designed. that info is DIRECT from icom & yaesu..... |
Rldrake
New member
Username: Rldrake
Post Number: 9
Registered: 1-2006
| | Posted on Saturday, January 07, 2006 - 4:41 am: |
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What are you using for a meter? Is it a TRUE pep reading meter? Is the meter powered by battery or a power supply? |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 996
Registered: 6-2004
| | Posted on Saturday, January 07, 2006 - 11:58 am: |
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The type of meter shouldn't matter. Modern HF rigs aren't designed to be AM monsters. They're low level modulated because they're designed for SSB work. Not too long ago, some HF rigs didn't even have AM built into them.
I agree with the advice given earlier - Set the carrier to 25 watts or less. While watching the ALC meter function adjust the microphone gain so the meter just barely moves on voice peaks and then back it off so that the meter doesn't move at all on voice peaks. Don't worry about the meter. You should sound excellent on AM. If you want to be "louder" just turn on the speech processor before adjusting the microphone gain or use a compression microphone like a Shure 526T or Turner +3. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2189
Registered: 7-2004
| | Posted on Saturday, January 07, 2006 - 5:16 pm: |
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with the processor ON, the non compression +2 gets better reports on AM & SSB then the +3, on my ic735. the 526t i'm told sounds better then any other mic i've tried on it, including a heil icom specific mic.
i'm using a diamond sx100. my ft757gxII did not exhibit the downward swing on AM like the ic735. when adjusted right, the icom sounds better then the yaesu did. while i had been told the icom sounded real good on AM, i had it checked & saw by way of o'scope that it was good-irregardless of the watt meter swing. adjustment of the front rf power control has little effect on AM quality. if the rear-mounted CARRIER CONTROL is over 30 watts, the radio when on AM still sounds as though it's on SSB. you just cannot have it show massive amounts of swing like a CB & expect it to sound good. especially on AM. |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 999
Registered: 6-2004
| | Posted on Saturday, January 07, 2006 - 6:33 pm: |
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I really wouldn't use two stages of compression unless the microphone's compression level was really light - essentially just to get the volume nice and level. The Kenwood MC-85 does that, and does it very well - especially for VOX operation. Even with the compression level as high as possible, it doesn't have the same effect as the radio's processor.
I guess I wasn't specific enough about setting the carrier level, so Pat used capital letters to stress carrier control. My HF rig has the carrier control right next to the power control, so I forget that some don't.
With the radio at full power(which is usually about 100 watts PEP) you want to adjust the carrier level to 25 watts maximum so the radio is capable of achieving 100% modulation. Some radios may need to use an even lower carrier level so they can get to 100% modulation. You might need to play around with your particular radio to find where it works best, but 25 watts is a good starting point. |
Bbmfic
Junior Member
Username: Bbmfic
Post Number: 47
Registered: 1-2003
| | Posted on Friday, January 27, 2006 - 12:50 pm: |
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as all of those radios they are set for 25 watts you have to get in there & adjust them up if you think about it the radio will do 100 watts on ssb it will also on am also that doesnt mean to run it a 1oo watts turn the rf power up on the front of the radio & adjust it inside to 100 watts now you will have all the fwd. swing you want as long as you use a 10 watt dead key turn up the mic gain & watch it swing my ft 1000 mp mv swings from 10 watts to 65 watts with no trouble at all the reason i say use 10 watts dead key is because some of these radios have auto tunners in them & they wont work untill they see 10 watts & you will also take it easy on your finals with 10 watt dead key try it you will like it |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1051
Registered: 6-2004
| | Posted on Friday, January 27, 2006 - 5:49 pm: |
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What? The reason you don't want more than a 25 watt carrier is that at 100% modulation, an AM signal with a 25 watt carrier will reach 100 watts PEP.
Also - AM doesn't swing! At 100% modulation you will see only a 50% average power increase from the carrier alone. If you are using voice to modulate the carrier you will only see about 10% to 30% average modulation. 10% for raw voice, and 30% with simple compression. If you're using an AF or RF clipping speech processor, the levels can be significantly higher.
Take 30% of the maximum of a 50% average power increase, and you're looking at only a 15% power increase from the carrier power level. That isn't much swing.
Why was I discussing AVERAGE power? Because analog meters don't show PEP with voice. They might get close with a constant tone, but I wouldn't count on that either. True PEP readings can only be shown with an oscilloscope because it's fast enough to follow the 3kHz speed of voice. |
