The Southern Ontario/WNY Radio-TV Forum / Wanted: An Engineer To Explain This HD Radio Issue

**Posted by RadioActive** February 24, 2025 8:33 am

I've always admired engineers, who understand the technical complexities of broadcasting. My knowledge of this stuff is limited to a station broadcasts a signal and I turn on my radio to listen to it.

Which brings me to this article that argues the pros and cons of something called "symmetrical" vs. "asymmetrical" sideband power for HD radio signals in the U.S. The debate appears to be whether one type of propagation causes more interference than the other, with stations asking the FCC to approve the latter so they can increase power on their HD signals, allowing them to reach farther.

It seems like the FCC is reluctant to allow the change, but many stations are lobbying hard for it. My first thought, in my limited understanding of this stuff, is how power increases in Buffalo HD radio, should it happen, would affect stations across the border in Canada. We already know HD interferes with some distant signals as it is.

But perhaps someone here can explain this in layman's terms. What could a power boost for HD stations mean for radio down south - and those of us in the Great White North?

Request For Expanded Reporting On HD Radio Signals Faces More Opposition

**Posted by tvguy** February 24, 2025 11:28 am

Skywave will know this answer, but I’ll give it a try. My experience with assymetrical goes back to a severe interference case in Vancouver/Bellingham. The first adjacent on KISM 92.9 (Bellingham) operating in HD was causing severe interference to analogue CKYE-FM 93.1 Vancouver. Over a day or two, back around 2014 or 2015, the stations cooperated and the “upper sideband” - closer to 93.1 was lowered, and measurements were taken. KISM abruptly stopped cooperating on the 2nd day of testing. I had understood at one time that Durham Radio might have used assymetrical on KX 94.7 Hamilton to protect their analogue Rock 95 signal cominng from Oshawa. Not sure if that was a test or made permanent. Based on the engineering measurements in the Vancouver situation, there was some noticible reducton of interference to 93.1 Vancouver, particularly as you got closer to the boarder around White Rock BC. But as I noted Saga walked away fron the testing. I don't know the parameters of the proposal to the FCC, and whether the energy directed to "one side" of the sideband, could significantly exceed the energy levels currently permitted with symettrical HD transmission. Skywave?

Last edited by tvguy (February 24, 2025 11:29 am)

**Posted by rk12** February 24, 2025 11:29 am

An HD radio signal is transmitted above and below the analog frequency.HD radio transmits 2 signals .Currently both the upper and lower usually have the same power level.Some broadcasters want to increase the power one of 1 of signals to provide better reception where there is maybe not an adjacent channel to interfere with.In GTA with no coordination of signals could result in more adjacent channel interference of distant signals.1 FM station with HD radio can take space on dial of 3 analog stations.

**Posted by RadioActive** February 24, 2025 11:39 am

Thanks for the answers.

I have no idea what this portends, but if there's a lot of interference in Canada from neighbouring U.S. signals, I can only imagine what station owners and the CRTC will do - especially since Trump has appointed his own people to the FCC and they have absolutely no interest in Canada's issues, regardless of what international agreements say.