AM Modulation visited via Spectrum Analyzer

[ss8541]

am i sure???? is pig pu$$y pork? the answer to both is YES.

and yes -6dbc for the sidebands is 100%. so just lets plug this into the equation. sorry if the equation itself is not clear enough. let me see if i can make it easier to read. sorry, but i am not a math teacher..just a solver. i make my own equations, so they may not look text book, but they sure as hell turn out that way.

modulation % = 2 ( inv. log dbc/20)
mod % = 2 (inv. log -6/20)
mod % = 2 (inv. log -.03)
mod% = 2 (.5012)
mod % = 1.0024
now change the decimal to a percentage.
1.004 * 100 = 100.24%

i see you did not use the negative designator in your example so even if you would have followed the math (the way it was in my head anyway) you would have not arrived at the right answer.

now plug in -12dbc and let me know what you get.

 

[DTB Radio]

I did a bit more reading, and I realized what I was seeing. Simple IMD. For whatever reason, even with all the reading I've done over the years, I've never picked up on the fact that IMD in an AM signal was harmonically related to the modulating signal.

 

[freecell]

i have a problem. when i perform the function -6/20 i end up with -0.3, not -.03.

modulation % = 2 ( inv. log dbc/20)
mod % = 2 (inv. log -6/20)
mod % = 2 (inv. log -0.3)
mod % = 2 (.5012)
mod % = 1.0024
now change the decimal to a percentage.
1.0024 * 100 = 100.24%

since the math still plays out i'm assuming it's just a typo.
correct me if i'm wrong.

modulation % = 2 ( inv. log dbc/20)
mod % = 2 (inv. log -12/20)
mod % = 2 (inv. log -0.6)
mod % = 2 (.2512)
mod % = .5024
now change the decimal to a percentage.
.5024 * 100 = 50.24%

 

[ss8541]

i have a problem. when i perform the function -6/20 i end up with -0.3, not -.03. ..............

since the math still plays out i'm assuming it's just a typo.
correct me if i'm wrong.

yes, i meant to type -0.3 but i typed -.03 by accident.

 

[freecell]

stuff happens. good afternoon to you richard.

 

[hvfc6120]

HP 141T Spectrum analyzer

I have a HP141T/8553B/8552B Spectrum Analyzer
HP8640B rf signal generator and HP 100mhz 4ch digital Scope.

Can anyone guide me in the setup of this unit for testing and tuning cb's. ie, what were the settings used on the SA at the beginning of this post. I have a Cobra 29 LTD and 25 LTD and want to get some experiance tunning them. I have used the late model HP Spectrum Analyzers HP8590E etc. but they pretty much set themselves up. I would like to get a grasp of were to start the process, What other equipment would i need?
allready have Attenuators, rf Loads, etc.

Any help would be greatly appreciated.

 

[DTB Radio]

Well, for starters, tunr on the Spec-an and leave it on for several days to stabilize thermally. I used the lowest RBW setting and narrowest filter, which meant VERY slow scan time. I set up the display for a fairly long storage interval, and locked it after it made a full scan.

The scope can juts be set for the slowest scan without flicker and to whatever vertical setting works best for you.

The generator should be set to whatever output specs are called for in the alignment procedure for the radio you are tuning. If your generator isn't calibrated, or if you're like me and have accidentally keyed too much into it and damaged the output attenuator module more than a few times, set it for the lowest output that still gives a fair sinewave on a scope when looking at the speaker output of the radio.


On a side note, I plan on putting together an automatic switch that will instantly switch me to my dummy load whenever I key, preventing any further "accidents".