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Author Topic: Where are all the OOs?  (Read 1983 times)
K1BXI
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« Reply #15 on: October 07, 2009, 06:12:10 PM »

"I work a lot of gen class ops on 3905 ccn."

I work them on 3805 too, since their band edge is 3800.

Your filter may be 2.6 at 6 dB down, but how wide is it at 30 or 60 dB down? That's what you need to know.

John
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K1BXI
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« Reply #16 on: October 07, 2009, 06:22:05 PM »

Whoops...........need to read closer...3905 ccn is on 7178. How about calling it the 7178 ccn then.

(just kidding)

John
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W8JI
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« Reply #17 on: October 08, 2009, 05:00:08 AM »

Although I doubt any radio except one with an exceptional problem would get nailed, 7178 is too close for nearly all rigs to technically be "safe".

The 3 kHz is some baseless Ham myth started by people who probably don't know how SSB transmitters work.

First, the filter is offset from the carrier. A 2.7 kHz filter in a radio tuned to 7178 LSB is NOT from 7178 to 7175.3. The filter is always offset by a few hundred Hz, so typically a 2.7 kHz filter in a radio tuned to 7178 extends from about 7177.7 down to 7175.

The bandwidth spec is normally the 3-6 dB point, depending on the filter or manufacturer. This means at 7175 your signal would be only around 3-6dB down, and you signal would also have emissions related to modulation down to perhaps 7172 or lower at -30dB down. If you look at ARRL reviews, many radios are only -25 to -35 dB down for IM3, and IM3 is stuff outside the filter passband.

A narrower filter would also sound pinched and not do much for IMD bandwidth. It also would not do much for the suppression problem, because when a narrower filter is installed the carrier offset is generally increased to keep the filter centered in the voice range.

I think 7178 is not a smart choice for a general, and not a smart choice for the net if they want generals to participate.

The applicable letter of the law is:

ยง 97.307   Emission standards.
 
(b) Emissions resulting from modulation must be confined to the band or segment available to the control operator.

(d) For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission.

Notice most of our radios, when on SSB, fail to meet the current FCC law if we consider IM3 products spurious emissions. The lucky thing for us is they rarely enforce the law.

Tom
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KG8JF
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« Reply #18 on: October 08, 2009, 06:14:12 AM »

The OO subject brings up the point of mistuned signals on PSK 31.  I wonder if there are any OOs on 20 meter psk.  I see guys with very wide signals and several orders of sidebands.  When I can, I go back to them and ask them to cut back on their audio drive.  Sometimes I get the feeling that they don't understand what I am trying to tell them.   The last thing I want to be is the PSK police.
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W8JI
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« Reply #19 on: October 08, 2009, 07:18:59 AM »

You are in a tough position. When a guy has a terrible signal, it is now considered bad to let him know. Hams (or society) have turned something very good that set Ham radio apart, self policing, into something bad.

I notice the very same thing with PSK and audio through digital modes, and on SSB from fools who crank the bass and treble up to sound like HiFi. Tune around on some of the "full audio" stations and look at the useless distortion products that are up or down an abnormal amount.

The other day I heard a station in Spain on 40 who sounded all bassy and HiFi, and with only a 20 over 9 signal I could hear his junk about S-5 5-10 kHz down.

I noticed when I tune 20 SSB, there are some terrible signals.

I think maybe testing and exams have ignored how to run a transmitter to the point where it hurts us, and this is coupled with a social stigma against being honest if it in some small way hurts someone's ego.

These attitudes almost immediately precede the collapse of a social order.

Tom
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W8JI
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« Reply #20 on: October 08, 2009, 07:32:01 AM »

By the way. I should point out an example about testing.

Part of the test should always be about bandwidth and where the signal is really at. Without knowing that the operator has no clue if it is in band or out of band.

If I actually have a 2.6 kHz bandwidth SSB transmitter and I'm on 7200 LSB, where is my signal? The truth is, it is NOT on 7200. It is at an offset below 7200 minus the bandwidth on LSB. If the radio has a typical carrier offset of about 350 Hz, your signal starts at 350Hz below 7200 and goes down 2.6 kHz from there. That is probably a -6dB point, not a infinite point. So at 60 dB it is likely half again as wide for filtering. Not only do you have that, you have IMD products that are typically 30 dB or so down.

When we get our heads around how a transmitter really works, we can see it is stupid to work 3 kHz up from the band edge on SSB if we want to be safe. We can also see how pumping up the bass and treble increases off frequency splatter if we know how power supplies, transmitters, and intermodulation works.

I'm not saying people shouldn't be free to run enhanced bass and treble, just that they need to have some polite sense when and where to do it. As a people, we are loosing common sense.
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W4HV
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« Reply #21 on: October 08, 2009, 09:00:21 AM »

OO's Have a thankless job! Having been one myself I can speak from experience..Actually there are 2 assumptions made about the program that are false. Experienced ops who care about their hobby are those that are usually OO's.

 First they are the band police and should be able to stop all bad things from happening..Its true they listen and advise the commisssion with field reports but they have NO ENFORCEMENT POWERS!..They do send advice cards to people..Well all know how it goes with advice..
 Second they are out to get people...No not at all!..If one gets a card from an OO its up to you to make the choice to do something about it..
Like with all good things there are critics and crybabies as well as advocates..Having done the job for several years in the past I do understand why some one may ask where they are..The correct answer is LISTENING!
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KA2UUP
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« Reply #22 on: October 08, 2009, 09:24:21 AM »

One thing is being an OO, another one is an idiot who behaves like the supreme channelmaster of the sniverse.

The good OOs send cards when they don't have to do it, that is, when they hear an operator doing the right thing and encouraging them to continue good operating practices.  Or, they will come into your QSO and advice you of something without insulting you.

OOs are out there, alright, but please, observe and advise responsibly!

Warmest regards from Bart @ KA2UUP
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K2TY
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« Reply #23 on: October 08, 2009, 10:54:42 AM »

"Part of the test should always be about bandwidth and where the signal is really at."

I believe this is covered on the general test.

"It is at an offset below 7200 minus the bandwidth on LSB. If the radio has a typical carrier offset of about 350 Hz, your signal starts at 350Hz below 7200 and goes down 2.6 kHz from there."

Tom my FT 897 has adjustments for carrier offset. The default position is 0 hz. Is my signal offset 0 hz or is it really offset 350 hz?
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W8JI
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« Reply #24 on: October 08, 2009, 06:24:57 PM »

The problem is what the manufacturer means by zero.

If the radio has either analog or digital SSB filtering, the carrier HAS to be offset from the "filter passband" or the rig will sound like heck.

This is because the most useful information content of voice starts at a few hundred Hz and goes up to about 3000 Hz. Passband offset technically can't be zero or power would be wasted by broadcasting useless stuff between 0 Hz and a few hundred Hz. They probably call the normal offset zero, and let you wiggle it higher or lower from there.

Tom
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W6RMK
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« Reply #25 on: October 10, 2009, 10:36:15 PM »

w8ji commented:
"
The other day I heard a station in Spain on 40 who sounded all bassy and HiFi, and with only a 20 over 9 signal I could hear his junk about S-5 5-10 kHz down.
"

that could actually be legal, if I understand what you're saying.. S5 relative to 20 over 9 is what, about 40-45 dB?  If those "spurious emissions" are 40 dB down (the notional limit), you'd still hear them..

Sort of the Tx phase noise or IM3 problem in a different form..
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W8JI
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« Reply #26 on: October 11, 2009, 04:39:00 AM »

There is no actual "dB number" for spurious, splatter, or keyclicks for the end-user in the USA. The letter of the law simply says we are not allowed to cause interference to adjacent frequencies from modulation products.

The minimum manufacturer's criteria today effective January 1 2003 is a *minimum* of -43 dB.............

(a) No amateur station transmission shall occupy more bandwidth than necessary for the information rate and emission type being transmitted, in accordance with good amateur practice.

(b) Emissions resulting from modulation must be confined to the band or segment available to the control operator. Emissions outside the necessary bandwidth must not cause splatter or keyclick interference to operations on adjacent frequencies.

(c) All spurious emissions from a station transmitter must be reduced to the greatest extent practicable. If any spurious emission, including chassis or power line radiation, causes harmful interference to the reception of another radio station, the licensee of the interfering amateur station is required to take steps to eliminate the interference, in accordance with good engineering practice.

(d) For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission.
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W6RMK
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« Reply #27 on: October 11, 2009, 07:36:25 AM »

I confess the rules are somewhat vague (say, compared to an actual spectral mask.) on the other hand, that's what's nice about amateur radio.. nobody is going to bring the hammer down on you as you tinker on something homebrew.  Commercial products are probably a different matter...
but

(a) No amateur station transmission shall ... in accordance with good amateur practice.

>>excellent..all we have to do is define "good amateur practice" <grin>  I certainly wouldn't want to impose a strict limit based on theory (After all, the"information content" of many QSOs is pretty limited)

(b) Emissions resulting from modulation must be confined to the band or segment available to the control operator. Emissions outside the necessary bandwidth must not cause splatter or keyclick interference to operations on adjacent frequencies.


>> but where do "emissions" stop.. is it "detectable", is it "43 dB down from the peak", etc... This is tough to evaluate objectively, except for the "interference to ops" aspect, but even there, that's subjective.  If I'm radiating a kilowatt, and my phase noise is -90dBc at 10 kHz away, that's still going to cause problems if my neighbor is 10kHz away and looking for signals at the noise floor.  Is that intefering?  How would I know who's out there.  In the commercial world you do compatibility analyses, ring-arounds, self interference testing, etc.  And, you know the transmitter/receiver/antenna configuration.

Back to "good amateur practice" I suppose, and folks who can gently educate other folks on what is reasonable and practical.

(c) All spurious emissions from a station transmitter must be reduced to the greatest extent practicable.... in accordance with good engineering practice.

Another subjective "good engineering practice" (different than "good amateur practice" from (a)??)



(d) For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission.
 
The only spectral mask kind of requirement in there, and as you've pointed out, one can meet this particular requirement, and still be might annoying to others on the band.
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W8JI
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« Reply #28 on: October 11, 2009, 08:49:02 AM »

The law is always pretty clear in that the most stringent rule can be applied.

If your splatter or a spur causes a problem off frequency, it is up to you to correct it. This doesn't mean if a problem 44 dB down causes a problem it is OK. It is only OK to sell that gear, not to operate it where or when it causes a problem.

We added harmonic traps here because even though the harmonics FS level was around -60 dBc, another station 10-15 miles away was complaining. There is no logical or reasonable way to say "put up with it buddy, we exceed the minimum requirement." We have to make it go away, because it causes a problem.

Think back to when the FCC did enforcement. If they heard a harmonic that was out of band, the station was sent a warning or a citation. They didn't ever say "If it is xx dB down at your house, don't worry." They said basically said we can hear it...it might bother someone...so fix it.

A similar thing applies to commercial stations. Even though a BC transmitter harmonic or IM product might be 83 dB down, if it causes a problem determined to be from the spurious they tell them to fix it.  They don't ever say "it's OK if you bother airplanes flying overhead because the spur you have is -85 dBc".

I know of one FM station that had to add traps and shielding to knock a channel 11 or 13 harmonic down well over 100 dB, because that TV channel was wiped out in the neighborhood of the FM station. They had to make it -35 dB below legal "minimum" levels.

The blessing and curse today is the lack of policing. It is a blessing because we aren't bothered with pink slips, and a curse because there is more trash bothering things even though technology or state of the art has greatly improved.

It really is a very orderly well-planned system, if they enforce the rules as written and if we all play nice with each other.

Tom
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W5HTW
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« Reply #29 on: October 11, 2009, 10:16:22 AM »

I decided to do some experiments.  Using my FT897D and a general coverage receiver that that does NOT have selectable sideband coverage, I set the 897's indicated frequency on 7200 khz for LSB.  I tuned the signal in on the GC receiver.  

And that told me something I had not considered.  The 897 actually shifts its "carrier point" upward by the offset amount, away from the indicated frequency.  So the 'carrier" (not heard since it is suppressed) is actually shifted upward by 2.5 khz!  Hmmmm.  That put the center of my voice bandpass on 7200 khz.  

That meant the extremes of my voice bandpass were definitely below 7200 khz.  Were I not permitted to operate below 7200, I would be operating illegally.  In fact, only a one khz tone would put me directly ON 7200 khz, and even then there would be side emmissions below and above that point.  

But the carrier point is shifted.  If the carrier point were to remain on 7200 khz, I would be transmitting entirely below 7200 khz!  

You can reverse the discussion for USB, of course.

With those results in mind, in the 'real world,' I would have to actually put my dial indication at the very minimum 7.203 khz to be safe (if, as in this example, I were not permitted emissions below 7200.)  But if I did that, I probably WOULD be safe, due to the carrier being 2.1 khz above my indicated frequency.

But... let's switch to AM mode.  Now the carrier point is NOT shifted.  My indicated frequency is 7200 khz, and that is where my carrier center point is.  (Same is true of FM)   That means my 3 khz bandwidth is 1.5 khz below 7200 and 1.5 khz above it.  WAY illegal.  

That internal offset can get you into a LOT of trouble!  Or it can keep you safe.  

I had experimented with that carrier offset before, using my Collins S-line and confirming it with my Drake B-Line.  You have to know the offset before you can even begin to determine if you are legal or not, if you insist on operating close to band edges!  

Good luck with that!

Ed
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