want to put a bigger kicker on a connex

I have set up many 1000's of radios for truckers over the last 40 years and many times have tried to inform them that the Key low swing high is just not good idea, I will also say that if they insisted on that I would do all I could to make it happen for them and make it work as good as it could work.. That being said if you want to talk about it just remember Brodcast radio stations will produce a carrier of many 1000's of watts and there forward power is nearly none existent, but you can hear them very loud and very clear for very many miles...

 

I agree with Child of God's assertion that too much swing = splatter. And even with low dead key and modulation limited to 100%, if the radio is tuned with *only* a wattmeter, i.e., without a spectrum analyzer, so that the 2nd harmonic trap (a/k/a TVI Filter) stage is tuned for maximum output, and THEN the drive is turned down, the signal out of the radio will still have a large component of harmonics. Merely having low power doesn't necessarily mean that the signal is clean, and most amps made for CB service have little to no band filtering, ergo garbage signal in will yield massively powerful garbage signal out. And an unfiltered amplifier will likely generate more spurious signals, increasing the bandwidth of that garbage.

By at least making sure the signal driving the amp(s) starts out clean, the changes are increased that the output of the amp(s) will be clean. And a low pass filter at the output of the last stage will help keep your wattmeter from reading all that extraneous spectrum.

More power shown on the last wattmeter does not necessarily mean that that power is all on *just* the frequency you're dialed up on.

73

P.S. Child of God -- I love your sig file. I remember seeing a simplified definition of the Big Bang Theory: "At first there was nothing. Then it blew up."
Thought you'd like that.

 

Vintech -- I must respectfully disagree with the part you put in bold font.
If you ever get a chance to hear an AM broadcast station during a period of dead air -- which they abhor except for tests -- I think you'll note that that carrier CAN be heard nearly as far as the modulated signal. A 100% modulated carrier has exactly 50% more power than the carrier alone. And commercial broadcast has some leeway for a small percentage of going over 100% forward modulation because they have a clear channel within their prescribed coverage area, so they're not competing with hundreds or thousands of other channels on the same frequency, at least during the daytime. At night, most stations are required to reduce their output power because of MW (medium wave) skip, when AM broadcast DX stations can often be heard from thousands of miles away. There are a few so-called clear channel stations (KFQD in Anchorage on 750 KHz, near where I used to live, was one) because before the advent of GPS and Loran-C before that, those stations were used by aircraft in flight for ADF bearings so there was a reliable direction to help set a course.

AM stations usually employ a device called a Volumax® to keep their average modulation way up near the legal maximum so they could reach the farthest possible, instead of having lots of "swing", which would only let stations at the periphery of their coverage areas hear the audio peaks in the programming. Keeping the average RF output high makes for a consistent range, at the expense of any sense of dynamics in transmitted music programs. But they will sound louder at the extreme range of their coverage area. The Volumax is a compressor that brings up the quieter bits of audio so that they drive the transmitter as hard with modulation as the loudest bits.

Broadcast FM stations, having no variation in their output power with modulation, don't rely on peak modulation to enhance their power (and therefore range), so music on FM sounds more realistic -- pianissimo passages "carry" as far as fortissimo (or even triple forte) ones. We classical musicians get to enjoy a range of relative orchestral music volumes without suffering the loss of the signal when the low strings and brass drop out

Those same AM broadcast stations, while being allowed to run their forward modulation over 100% (to an absolute max of 125% on "an infrequent basis", which is poorly defined), are still required to keep their negative modulation limited to 100%. At 100% negative modulation, the transmitter is right on the verge of cutting off, introducing splatter. Commercial AM stations are also limited to 5 KHz modulating frequency (audio) to limit their bandwidth to their allotted 10 KHz channel. While that's seldom a problem with voice transmissions (like ours on CB), music that's limited to 5 KHz loses a whole lot of fidelity. And too much asymmetric modulation, like huge forward modulation with no more than 100% negative modulation, grossly distorts the audio that's transmitted.

So a CB station that's running a carrier of 2 watts should peak at 3 watts with 100% modulation. Much more than that and the transmitter will cut off on negative peak, causing splatter. Since wattmeters aren't fast enough to swing from positive peaks to negative peaks (also known as "off"), watching just a wattmeter gives a false impression of how good a signal is; the splattering signal (spurious transmissions) still go out the transmission line. The signal may be heard farther away in distance, but also "farther away" from the channel/frequency they intend to be on, so all that stuff outside the intended channel's bandwidth is, at best, wasted and at worst, causing harmful interference to other channels, possibly even outside the 26-28 MHz band, like up into VHF occupied by industrial, commercial FM broadcast, and aviation freqs. And the spurious signals that aren't harmonically related are difficult to predict, as in the case of the lad in Kenai, Alaska who recently got gigged by the FCC for interfering with HF aircraft frequencies. At last count, I think they were going to take away his birthday....

But back to the original point, I believe you'll find that the forward power at AM broadcast stations who are transmitting dead carrier (not often, but sometimes they have to) will be about 75% of their modulated power -- hardly non-existent -- and audible nearly as far away as their usual signal with modulation.

Best wishes and 73

P.S. My experience includes many years doing engineering at broadcast stations at both AM and FM stations.

 

LOL...Yeah I do like that one!

 

Yes you are correct! Imagine That? What I was attempting to do in my usuall layman terms kinda way was get across to whoever was listining is that Broadcast stations that produce say 50K watts don't idle at 5K watts and modulate to 50K watts. I have found over the years if I try to get real heavy with truckers when trying to educate them as to how things work they all glassy eye'd..and then later hear them on the radio saying "I wish I knew what that guy just said"And I also have a degree in electronics and have repaierd communications for 40 years..

 

Vintech -- I hope you realize I wasn't contradicting your post; I know that you know your stuff. It only occurred to me as I read your post that some folks might be getting the gist of it wrong, and would still be insisting on "as much swaaaannng as you can get" from their techs.
It's neat to see posts from folks who both know their stuff AND have been doing this long enough to have a lot of real-world experience. I enjoy seeing your posts; they're usually very clear to readers, I believe. A lot of shops have, errr, "techs" who have no more tune-up gear than a DVM, a pair of dikes, and a Dosy meter set for Peak <shudder!!>

73

 

No Problem handlebar I should not have benn so lazy in my post. Sometimes you need someone to remind you of that.. I will try in the future to more or less post in 2 lanquages, so to speak! I will be more active posting as I will be getting an operation this week that will keep from working for about 6 weeks but not from typing so I will need a good proof-reader on standby LOL..