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[Articles Home]  [Add Article]  

The Band Edge- How Close is Too Close?

from Duane Traver WV2B on April 9, 2001
View comments about this article!

The Band Edge- How Close is Too Close?

By Duane Traver, WV2B

It was a situation heard all too often. In fact, it can be heard almost every contest. A DX station calls "CQ Contest" on 14349 KHz. Strings of US stations answer and exchange the contest exchange. But in addition another voice can be heard.

Besides the stations exchanging contest reports another voice rings out- "You're out of band stupid, don't you know the rules." Some contesters are bewildered, doesn't the band go to 14350? Others are argumentative- I am not out of band, they contend.

Obviously the mystery voice is not handling things in a proper manner. After all, if the stations he is condemning are out of band so is he. In addition, he is not identifying his transmissions. But why do these arguments keep erupting? Does this guy know what he's talking about?

The Rule

If the band goes to 14350 KHz, then contesters can just set their dials to that frequency and operate- right? Wrong! The crux of the matter is found in FCC rule 97.307, which reads in part: "Emissions resulting from modulation must be confined to the band or segment available to the control operator."

What must be taken into consideration is the fact that the frequency displayed on the radio's digital display is the carrier frequency. A suppressed-carrier single-sideband signal is considered to be 3 KHz wide. So, for an USB signal to be confined to the 20 Meter Amateur band, the frequency displayed on the transceivers digital dial should not be higher than 14347. That may even be too close unless the transmitted signal is attenuated by at least 40 dB at 3 KHz. Of course, the same goes for a LSB signal transmitted near the lower end of a band or segment. Please see illustrations A and B below for help visualizing the situation.

               USB Signal
            ^^^^^^^^^^^^
I--------I--------I
347   14350   353

  A. USB signal transmitted with dial frequency of 14350 KHz.

LSB Signal             
^^^^^^^^^^              
I---------I--------I
147      7150       153

B. LSB signal transmitted with dial frequency of 7150 KHz.

So, the fellow telling all the contesters that they were out of band was right! But, is it a big problem? Obviously more education is needed on this particular rule. In the 2001 ARRL DX phone contest one Dx station was heard running US stations on 14349 KHz. in excess of 5 hours straight with a steady stream of US callers. Most were Extra class licensees.

Although certainly the majority of these callers didn_t realize they were violating an FCC rule, the action could result in an FCC warning, ARRL OO notice, or perhaps an argument from a frustrated fellow contester as mentioned at the outset of this article. Since all contesters who submit a log sign a statement that they have followed their country_s Amateur regulations they should be willing to take this rule into consideration and modifying their operation as needed.

In addition, contesting ethics are involved. What if a station finds a clear running frequency by operating too close to the band edge, while his competitor perhaps fails to find a run frequency out of respect for this regulation? Or what if a multiplier is counted by working a station calling too close, while other stations don_t get the multiplier because they want to obey the rules? Perhaps such situations are part of what causes our mystery stations to vent their frustrations.

I hope you find this article of help in your contesting efforts. Further information about this particular FCC rule can be found on page 4-34 of the ARRL_s "FCC Rule Book." See you in the contests.


Member Comments: Add A Comment
The Band Edge- How Close is Too Close? Reply
Anonymous post on April 9, 2001 Mail this to a friend!
<<A suppressed-carrier single-sideband signal is considered to be 3 KHz wide.>>

Where does it say this?

What if I have (and use) 2.1kHz filters (in both the RX and TX path) - am I allowed to operate closer to the edge?
 
RE: The Band Edge- How Close is Too Close? Reply
by wv2b on April 9, 2001 Mail this to a friend!
Dear Anonymous,<P>
First question- From the "FCC Rulebook", page 4-34:<P>
"Amateurs commonly consider full-carrier, double-sideband AM signals to be about 6 KHz wide and single-sideband, suppressed-carrier signals to be about 3 KHz wide. Those bandwidths, however, are usually only 6 db down, and that isn't what the FCC worries about. Thus, to determine where you may set your VFO in relation to the band or subband edge for your class of license, you'll have to figure out where your signal is attenuated by 40 db."<P>
From "ARRL Handbook" under Frequency Measurement- transmitter Checking:<P>
"For phone the safety allowance is usually taken to be about 3 KHz, the nominal width of one sideband." <P>
2nd question- As the FCC rulebook points out it necessary to find out where the transmitted signal is attenuated by 40 db. Perhaps the manual specifies this, or the manufacturer could provide details.<P>
73 Duane WV2B
 
RE: The Band Edge- How Close is Too Close? Reply
by W4ZV on April 9, 2001 Mail this to a friend!
Dave, a couple of additional points:

1. For CW you should add roughly a minimum of 4 times your keying speed to the band edge due the the additional bandwidth CW keying consumes. If you are sending at 40 WPM, you should be a minimum of 160 Hz above the band edge and more if you have hard keying (i.e. clicks). This is only an approximation as you should really look at your signal to see where any -40 dB products are. I believe another part of the FCC rule states that, even if your sidebands/spurs/harmonics are down -40 dB and you cause interference to another service, you are technically in violation.

2. I believe ARRL Product Reviews having been showing spectrum analyzer plots of sidebands/spurs versus frequency for some time now. This should help all of us determine how close to the band edge we dare go.

73, Bill W4ZV
 
The Band Edge- How Close is Too Close? Reply
by K9AY on April 10, 2001 Mail this to a friend!
We all need to remember that a 2.1 kHz SSB filter does NOT pass signals from zero beat to 2.1 kHz -- the filter passband is offset to transmit audio frequencies from about 400 to 2500 Hz. With a filter having a 6:60 dB shape factor of 2.0, the attenuation will not reach 40 dB until about 3200 Hz! Fortunately, most modern radios have better filters than this, so 3 kHz is an acceptable rule-of-thumb guideline.

HOWEVER, we also need to consider IMD products. -40 dB for 3rd order IMD is high performance. Some XCVRs and "linear" amplifiers are only specified for -30 dB at their rated power, which means that IMD products out to 5 kHz and beyond can easily be in violation of FCC rules!

73, Gary, K9AY
 
RE: The Band Edge- How Close is Too Close? Reply
by KR0U on April 10, 2001 Mail this to a friend!
Don't forget to add dial accuracy to the mix. If your synthesized rig has 10Hz readout and a 10ppm reference oscillator, dial error at 29MHz is +/-(10+29x10)=300Hz. Add that to your filter skirts, and 3kHz is too close for comfort.

If your rig has a calibrated 25kHz marker, try this:
- Calibrate your marker to zero beat with WWV.
- Tune to the marker on the band edge, using the transmit filter (not narrow or cascaded receive filters, unless you transmit through the same setup).
- Tune into the band until the marker signal is gone.
- How far did you have to go? Your transmitted signal is AT LEAST as wide as your receive filter, probably wider (as K9AY and W4ZV have pointed out).
 
The Band Edge- How Close is Too Close? Reply
by kn0v on April 11, 2001 Mail this to a friend!
Funny that this subject came up. On many occassions, I
have heard some very prominent stateside stations operating .5 or 1 khz above the band edge during phone
contests. Their sidebands are clearly out of the band.
This is not anything new and am surprised it has just
now come up - it has been going on for years. Maybe
the owners of these stations should clean up their act.
 
RE: The Band Edge- How Close is Too Close? Reply
Anonymous post on April 11, 2001 Mail this to a friend!
KNØV: what band? Just ABOVE the band edge on USB is OK, just below the band edge on USB is not.
 
RE: The Band Edge- How Close is Too Close? Reply
by vk2cz on April 11, 2001 Mail this to a friend!
Fully agree with the band-edge, ie setting ones dial to 3799 (LSB) to keep within our 3794~3800 band limits.

In VK there is only a gentlemens agreement where the CW/SSB demarkation exists within a band. It is considered (From an SSB viewpoint) that to operate below 3555, 7035, 14115, 28200 with SSB is running at the edge (but perfectly legal), and under contest operations which push limits, these guidelines are pretty sturdy.

I recall the Swan 350 rig was great, as it showed where the voice modulation sidebands would sit when sitting on the 'dial' frequency. Old is not necessarily out of date.
 
RE: The Band Edge- How Close is Too Close? Reply
Anonymous post on April 12, 2001 Mail this to a friend!
You expect the "mystery voice" to identify, knowing he, himself, is out of the band? Duh.
 
RE: The Band Edge- How Close is Too Close? Reply
by N2MG on April 12, 2001 Mail this to a friend!
I worked a DX station in ARRL DX 2000 at the top of 15 meters (21448 or so). There was a smokey (OO) in the weeds writing down the callsigns of everyone who did. Left those bandedge guys alone this year. Alas...
 
The Band Edge- How Close is Too Close? Reply
by ZS6EZ on April 25, 2001 Mail this to a friend!
An extension to the logic that hasn't been mentioned, is that one could actually operate with the dial outside the band. For example, sitting on 28 299,7 would be perfectly legal if one had sufficiently sharp filter cutoff at 300 Hz. That being the case, sitting on 28 300,000 is actually perfectly acceptable, as it actually provides a 300 Hz guard band. From halfway around the world, it is very difficult to hold down a frequency when short skip is present, or when there is good propagation between the major centres. We are almost invariably in an antenna null to anyone in the major centres. The band edge is a very valuable resource in that regard, as it cleans up QRM at least on one side. For that reason, I've had my fair share of lectures from anonymous advisers, most of whom have been ill-informed.

For CW signals, the keying baud rate is around 83% of the speed in wpm. A popular contesting speed such as 35 wpm is just under 30 Bd. With well-shaped waveforms, the sidebands would not extend much more than 30 Hz either side of the carrier. However, waveforms are generally rather "hard", requiring a bit more bandwidth. W4ZV's rule of thumb (4 x wpm) is probably not far off the mark, leading to a guard band of around 150 Hz. Some big M/M entrants stretch this limit somewhat!
 
RE: The Band Edge- How Close is Too Close? Reply
by w8ji on April 28, 2001 Mail this to a friend!
We all better read the rules again. The rules do not say we are allowed to be close if the emissions are down 40 dB.

The rules say we are not allowed to have ANY emissions outside the band. It means exactly what they say. If you have ANY emissions at ANY level outside the band or segment you are allowed to use it is illegal.

The same is true for harmonics that cause interference.

-40 dB is not even a spec for this, it probably has been extracted by well-intentioned people from type-acceptance rules fo the minimum attenuation we must have at HF for spurious emissions. That actual rule is 50mW or -40dB (above certain mean power levels)....but that is a minimum for type-acceptance. It is NOT what can get us "busted".

What will get us busted is if we have ANYTHING they can hear outside the band or authorized segment.

97.303(b) kicks in at any time. It says "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 frequiencies."

It does NOT say, "but if you are 40dB down it is OK".

The rules are not "pick the one you like", and the rules for type-acceptance are not the same rules for preventing interference. If we violate any subpart, it is a violation. The rule is, none of our clicks or sidebands can extend outside the band or segment we are allowed to use.

73 Tom
 
The Band Edge- How Close is Too Close? Reply
by KL7HF on May 10, 2001 Mail this to a friend!
Good comments, but need to go further to meet the
Commission's R&Rs.
There are 2 types of emmissions that are involved.
1) Those within the information envelope that are
necessary for communications.
2) Those not necessary for communications, referred to
as "Spurius Emmissions".
Your comments apply very well to the first.
The requirements for the second is that they not only
must be contained entirely within the Amateur bands, but must meet stringent attenuation standards. These
are quite often outside the bands, even thought the
carrier frequency is far enough inside to eliminate
out of band envelope information.
Cranking the mic gain up one more notch to get
through puts you in violation, as well as irritating
other contesters nearby.
By the way - those with the carrier oscillator set
quite far up the filter passband to get higher pitched
audio may very well exceed the 3 kHz rule. Remember,
a 2.1 kHz filter is rated only at the 6 dB attenuation
point. Setting the oscillator at 800 Hertz into the
filter passband means that you are only 6 dB down at 2.9 kHz.
 
RE: The Band Edge- How Close is Too Close? Reply
by lu9ay on May 29, 2001 Mail this to a friend!
1. For CW you should add roughly a minimum of 4 times your keying speed to the band edge due the the additional bandwidth CW keying consumes. If you are sending at 40 WPM,


.. ok I will try to remember to bring a calculator when looking for a clear frequency near the edge and do the math.. hopefully when I finish , the contest wont be over :)


matt
w1/lu9ay
 
RE: The Band Edge- How Close is Too Close? Reply
by VE2DC on May 30, 2001 Mail this to a friend!
Perhaps the contest rules should specify a minimum guard band. A few disqualifications would go a long way to curing the problem and end the pointless discussions of EXACTLY how wide an SSB or CW signal is. How high is UP anyway?
 
The Band Edge- How Close is Too Close? Reply
Anonymous post on June 9, 2001 Mail this to a friend!
Good point but it doesn't address the bottom band edge, on USB, as others have mentioned. I believe leading contesters believe you can go right down to just above 14.150, for instance.
 
RE: The Band Edge- How Close is Too Close? Reply
by k3ko on June 10, 2001 Mail this to a friend!
There has to be some limit describe the acceptable amount of suppression.

If one does a fourier transform of a single dit, he finds that there are frequency components which extend to almost light frequencies. Thus, there is no way for any time varying waveform to have zero energy beyond the fundamental and normal sidebands. Given this fact, zero can't mean zero. No technical way to achieve it other than QRTing.

Clearly the FCC knows this and won't hold a gun to the head of anyone who radiates a nanowatt outside his allocated frequencies. I doubt that they will persue anybody with properly operating type-approved equipment. Inteference with another service is perhaps the one exception.
 
The Band Edge- How Close is Too Close? Reply
by W5JLJH on July 26, 2008 Mail this to a friend!
I think the reason there is so much confusion is this;


1. All amateur radios - Factory or modified will trans
mit on say 7300 khz. If this is considered out of band then why do they work there?

2. If 7300 khz is out of band then make the darn things
stop transmitting at 7297? they work fine as intended from the factory.

3. Also the broadcast bands (AM that is) the new segment goes to 1700 KHZ, if you tune to 1700 KHZ AM on any night, you will hear more than one station transmitting on 1700 KHZ amd and is more than 5 khz wide! Do they majically end up as legal?

4. I Hate people who jump in on any frequency without identifying themselves. That is certainly a worse violation and is stated so and "is" in the rules.

5. Strap on a pair, spin the dial and use 7300 khz
and wait for the new icom and yaesu's to come out with more band clipped off the ends GEEESE! ??

 
RE: The Band Edge- How Close is Too Close? Reply
by W5JLJH on July 26, 2008 Mail this to a friend!
P.S. Also just to add another note.

If you tune to 7302 KHZ USB on any Saturday and listen to Air Force Mars, you clearly hear them down as far as 7297 Khz (even if you use 1.6 Khz filters. This is clearly another radio service, breaking the Law as you call it. Wheres the ruling there?

Time would be better spent donating your efforts to one of the ARRL organizations rather than running scared and bashing other operators for the shortcomings of the Laws of physics and radio design limits?

Don't constantly sit or the fence as it makes your neighbors nervous.
 
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