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I'm as far from an engineer as you'll find but I think I understand what the FCC is up to with this new ruling. Please feel free to correct this but it looks like they've approved allowing FM stations in the U.S. to broadcast with two separate powers for their HD signals if necessary, in order to be able to give different areas of their range priority. The idea is to cut down on interference for other stations.
I wonder how - or if - this will affect the delicate interactions between Canadian and American stations. I recall reading here some time ago that a few board members complain that some American HD signals can interfere with stations in their areas, especially when they're slightly out of the local's direct broadcast area. Theoretically, this should fix that issue.
Or potentially cause another one!
See how you interpret this and please feel free to correct me.
FCC Adopts New Asymmetric Sideband Rules for HD Radio
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HD radio is such a spectrum hog.Wipes out reception on adjacent channels on each side.So 1 HD station takes up 3 channels.So an HD station on 96.3 wipes out 96.1 and 96.5.
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As with many things FCC, there's a little less here than meets the eye.
By the time a rulemaking like this becomes official, the underlying technology has usually been on the air for a while on an experimental basis.
That's exactly the case with asymmetrical sidebands. The technology has been around for at least a decade. It's a standard feature included in current HD encoders from major transmitter manufacturers.
I just installed a new GatesAir HD FM rig here in Rochester and it's a simple menu item in the transmitter controls to adjust the symmetry of the sidebands.
The only thing that's new here is that stations wanting to operate in that mode no longer need to go through the formalities of requesting an experimental special authority to use it (and renew it every six months.)
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As for how the asymmetry works, it's actually pretty simple: an FM HD signal consists of mirror-image carriers above and below the center frequency of the analog signal. So when 93.5 added HD, Toronto listeners suddenly lost WBLK because the HD carriers actually sit on the same frequencies used by the 93.3 and 93.7 analog signals.
The FM HD standard says those upper and lower carriers are supposed to be transmitted at the same power level, which can be as little as 1% and as much as 10% of the analog power level.
Radios can usually decode HD from just one set of carriers, so the new rule lets stations use a higher power level on one set of carriers in situations where using higher power on both would interfere with an adjacent-channel station.
So for instance, my 103.9 in Rochester is short-spaced to 104.1 in Buffalo. If I wanted to crank 103.9 up to the maximum 10% digital power, my upper carriers would interfere with WHTT in areas between Rochester and Buffalo. So I can't run that power level on both sides - but in theory I could do it now on just my lower side and expand my HD coverage a few miles.
It's complicated along the border, of course. US signals have no protection from interference on Canadian soil and vice versa. So CKFM's HD is hard to lock in in Buffalo because of the WECK 100.1 translator. Nothing in this rulemaking changes that at all.
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Thanks for the simplified explanation. It's a complicated business but you made it easy to follow. Appreciate it.
But here's a much harder question to answer. You have the FCC while we have the CRTC.
Which of us has it worse?
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I am aware of a couple of instances where assymetrical sideband was used here in Canada. This may be out of date, but my recollection was that Durham Radio uses(used?) assymetrical on 94.7 Hamilton in order to offer some protection to their own 94.9 in Oshawa. There were experiments back in the 2014-2015 period with Saga’s 92.9 Bellingham - which was causing interference to 93.1 Vancouver - CKYE-FM. But Saga stopped “cooperating” on the 2nd day of the “experiment” and resumed symmetrical sideband. There might be another situation in Canada…perhaps Skywave knows.
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Yes Hamiltons 94.7 HD signal takes out Oshawas 94.9 analog signal here in Mississauga.Yet 94.9 says there GTAs rock station.
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Interference or not, it's coming. The FCC has approved this proposal in the U.S. It remains to be seen if it will affect any nearby stations in Canada.
FCC Approves HD Radio Change That Supporters Say Will Improve Signal Coverage