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Nighttime AM-HD now published in Federal Register !
On Aug 15, 7:12 am, wrote:
Say goodbye to AM nighttime DXing - the beginning of the end for AM radio: So when will be able to hear night-time IBOC on AM? Not that it would matter to me since I don't have an IBOC receiver (yet). Another local station is gearing up to go IBOC: 1010 WINS, which has been signing off on Sunday nights and plans on doing so for the next couple of months. Their antenna array is not "flat" enough for HD (whatever that means, I'm not a transmitter person). Stephanie Weil New York City, USA |
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Nighttime AM-HD now published in Federal Register !
Stephanie Weil wrote: On Aug 15, 7:12 am, wrote: Say goodbye to AM nighttime DXing - the beginning of the end for AM radio: So when will be able to hear night-time IBOC on AM? Not that it would matter to me since I don't have an IBOC receiver (yet). Another local station is gearing up to go IBOC: 1010 WINS, which has been signing off on Sunday nights and plans on doing so for the next couple of months. Their antenna array is not "flat" enough for HD (whatever that means, I'm not a transmitter person). A couple sticks of dynamite would flatten it nicely. dxAce Michigan USA |
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Nighttime AM-HD now published in Federal Register !
dxAcehole Supreme Commander United Militias (S.C.U.M.) wrote:
Their antenna array is not "flat" enough for HD (whatever that means, I'm not a transmitter person). A couple sticks of dynamite would flatten it nicely. dxAce Michigan USA Does your United Michigan Militia endorse the destruction of private property? Do you already possess the dynamite? Have the FBI been by to look at your weapons cache? Get help, you loon... mike |
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Nighttime AM-HD now published in Federal Register !
On Wed, 15 Aug 2007 14:55:00 +0000, Stephanie Weil wrote:
Another local station is gearing up to go IBOC: 1010 WINS, which has been signing off on Sunday nights and plans on doing so for the next couple of months. Their antenna array is not "flat" enough for HD (whatever that means, I'm not a transmitter person). "flat" refers to the impedance (and possibly the directivity) of their antenna system on frequencies near but not equal to their 1010KHz carrier. WINS's operating frequency is quoted as 1010KHz, but that's just their center "carrier" frequency. If WINS were to transmit "dead air", that's the only frequency they'd radiate a signal on. Once they start transmitting voice, they begin to have signal on adjacent frequencies, 5-7KHz either side of 1010. They might occupy a range between 1003 and 1017KHz. For the transmitter to operate properly, the "impedance" of the antenna system must be reasonably close to 50 ohms (and must have little or no reactance) at any frequency at which the transmitter might radiate a signal. A non-radiating "dummy load" is the only antenna that will be 50 ohms at *all* frequencies; any useful antenna for WINS will vary in impedance and reactance with frequency. Since WINS has been successfully using its existing antenna system for some time, one can reasonably assume its antenna system exhibits an impedance reasonably close to 50 ohms across the 1003-1017KHz range. IBOC adds digital carriers to the outer edges of the channel. For WINS it would extend from 995-1025KHz. If their antenna system is "not flat enough" that means the impedance in the 995-1003 and/or 1017-1025KHz ranges isn't close enough to 50 ohms, and/or there is too much reactance. A related problem would be with the directivity of the antenna. WINS is required to use a directional antenna system at all hours. The directivity of its antenna will also vary with frequency. It is possible the WINS system is close enough to 50 ohms across the IBOC band for the transmitter to be happy, but for its directivity to not be adequately maintained in 995-1003 and/or 1017-1025KHz. That would result in increased interference to other stations on 990, 1000, 1020, and 1030KHz. (beyond that which arguably would result simply from WINS's use of IBOC) There are ways of fixing this problem. They seem to involve computer modeling the antenna matching networks and finding new network designs that solve the issue. The process is neither fast nor cheap, and once the necessary changes are determined the adjustments must be made - the networks may require modification - and then measurements must be made to ensure things actually are working properly. This will be an issue for many directional stations - it's why I don't see September 14th bringing IBOC to a huge stampede of AM stations. WINS can afford the work. WKRP in tiny Podunk maybe can't. |
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