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The Band Edge- How Close is Too Close?
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Anonymous post on April 9, 2001
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<<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?
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RE: The Band Edge- How Close is Too Close?
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by wv2b on April 9, 2001
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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
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RE: The Band Edge- How Close is Too Close?
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by W4ZV on April 9, 2001
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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
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The Band Edge- How Close is Too Close?
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by K9AY on April 10, 2001
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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
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RE: The Band Edge- How Close is Too Close?
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by KR0U on April 10, 2001
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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).
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The Band Edge- How Close is Too Close?
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by kn0v on April 11, 2001
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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.
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RE: The Band Edge- How Close is Too Close?
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Anonymous post on April 11, 2001
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KN�V: what band? Just ABOVE the band edge on USB is OK, just below the band edge on USB is not.
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RE: The Band Edge- How Close is Too Close?
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by vk2cz on April 11, 2001
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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.
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RE: The Band Edge- How Close is Too Close?
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Anonymous post on April 12, 2001
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You expect the "mystery voice" to identify, knowing he, himself, is out of the band? Duh.
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RE: The Band Edge- How Close is Too Close?
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by N2MG on April 12, 2001
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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...
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