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New member and AM modulation % question.

morseguy

morseguy

Member
Jun 16, 2013
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Earth
Hi everyone.
New member here, long time lurker.
I've don't claim to know it all and certainly am not a technicion either but have been playing around with and using cb,ham,shortwave stuff since the 70's, I'm a HAM too.

I have a question regarding the new Galaxy DX94HP I recently purchased. It is advertised as a "100 watt max" radio. Out of the box it has a 35 watt deadkey with a swing to 100 watts. Wouldn't that be less than 100% modulation. I determined this with my Yaesu YS-60 PEP reading wattmeter that I have had along time and have verified its accuracy. This meter uses 12vdc for its op-amp circuit. The DX94 Service Manual specifies setting the high deadkey to 35 watts.
Once you turn up the AMC pot it swings easily to about 130 watts. Even if you turn the deadkey down to 25 watts.
Now if I remember correctly, isn't 100 % modulation four times the carrier? So if I'm deadkeying 25 watts and swinging to 130, whats my modulation percentage? If I turn the deadkey down to 5W it will swing to about 100W.

This is my first "export radio" and am a little confused. All of the HF rigs and cheaper CB's that I have had experience with on AM seem to not swing so wildly.
Is this just a hidden secret of export radios, they are cut back when they leave the factory and with just a few simple tweaks they let loose?
And what the deal with the obsession of having a low deadkey/high swing?

Hope I did not ask too much at once but look forward to the replies. LOL

73's
 

What you are seeing is a very common misconception about how AM mode works, and an advertising scheme. 'Big numbers' sells! Doesn't have to make any sense, just bigger numbers, you know? Lower that dead key a little bit past a certain point and you have suppressed carrier double side band! Not exactly AM anymore, huh?
- 'Doc
 
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That was always my contention why do you need swing on AM. If you want swing go ssb, and you're right swinging that much is darn near dsb. Yes its all marketing and people who really don't understand how radio works.
 
Ok guys im gonna ask a question if you dont mind please. I have a stryker SR-655HPC and a fatboy 4x2879 linear. I can set the dead key lets say at 100 watts from the linear and swing to 700 watts or up to 300 dead key and swing to the same. In your opinion what should i be dead keying? Yes im talking strictly am.
 
morseguy said:
And what the deal with the obsession of having a low deadkey/high swing?
Click to expand...


The guys that like to run AM into their amps figure that with a low dead key and lots of swing their amps will run cooler due to the lower demand placed on them by not amplifying a much high unmodulated carrier. If they would just run the damn radios as they should and use a decent amp meant for AM service then things would be fine and it could be run at the normal 4:1 carrier to peak ratio. Most of the loud and proud crowd has no clue as to what GOOD AM sounds like and they resort to something that resembles double sideband reduced carrier emission mode and shove it through a class C amplifier for even more feel good numbers.
 
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Sonic said:
Ok guys im gonna ask a question if you dont mind please. I have a stryker SR-655HPC and a fatboy 4x2879 linear. I can set the dead key lets say at 100 watts from the linear and swing to 700 watts or up to 300 dead key and swing to the same. In your opinion what should i be dead keying? Yes im talking strictly am.
Click to expand...


In my opinion, dead key no more than 125 watts MAX and peak to 500 watts MAX. however it sounds like you radio probably won't do those dead/peak numbers. I am just basing my answer on manufacturers ratings of the 2SC2879 BTW and NOT what people think you can get out of them. Actually if that Fatboy is a class C amp I refine my answer to dead key ZERO watts and peak to ZERO watts. Class C is for CW or FM modes and NOT AM or SSB.
 
Sonic said:
Forgot to add if i raise the dead key my swr's go up to high.
Click to expand...


SWR's? You mean ALL of them go up? :whistle:



SWR is ALWAYS singular. SWR. It is a ratio. No plural. SWR does not change with power. Are you recalibrating the meter before AND after changing power? I assume you are talking about the antenna SWR and not the SWR between the radio and amp. What you are seeing is likely the harmonics and crap generated in the amp being reflected from the antenna. You meter cannot tell the difference between your signal and the harmonics etc. Your true SWR is what you see with the amp OFF.
 
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Yes im recalibrating the amp every time with each adjustment of the power. So youre saying when i raise the power and i check the swr my external meter is giving me a false reading?
 
Sonic said:
Yes im recalibrating the amp every time with each adjustment of the power. So youre saying when i raise the power and i check the swr my external meter is giving me a false reading?
Click to expand...


Yup. The amp is generating crap off frequency and that is being reflected and showing up as a high SWR. Happens all the time with normal CB type amps.
 

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