Re: [IRCA] WHP 580 IBOC

[mwdxer@xxxxxxxxx (Patrick Martin)]

>>Hiss behind the audio... Yes, does happen. Some stations have a more
correct setup that others. The digital sidebands are sometimes less
confined to the correct bandwidths. For example, the 550 station had
extra sidebands at 27kHz either side of the 550 spot. While it was
within the FCC requirements, they were still there. The upper and lower
sidebands are supposed to be phased. One is -90° and the other is
+90°. That puts them at 180° and they null out in the analog band.
If the antenna system isn't perfectly flat on the load across the whole
spectrum, then some digital hiss would be heard as the null isn't as
exact. <<

It isn't just hiss behind the audio either, as in the case of KFBK 1530.
There becomes a echo hum behind with the hiss. I used to listen to KFBK
at night years ago, but not any longer as the noise drives me nuts. It
is very irritating to listen to. KFI has the noise too, but it isn;t as
irritating as it is and not as loud. The KFBK's noise often sounds like
a train behind their signal with a whoosing sound. Now on KCBS 740 is
now bad. KEX can be noisy too, so I never listen to them. KEX is worse
at night once the skip takes ahold of their signal. KSL isn't to bad.
Some are and some aren't.

>>And night skip does affect it, if there's a signal from an adjacent
IBOC station. WBZ-1030 is 30+ miles from Providence. KDKA-1020 IBOC
interferes with them at night. It affected one of my clients receiving
EAS at night. I had to use one of the large ferrite loops set to null
KDKA to fix that.<<

I think there is a lot more IBOC in the East than here. The NW has not
gone with it as much on AM. I think as I type this we only have a
handfull of stations in the NW. The ones I know run is 24/7 are
Tacoma/Seattle/Olympia/Everett  850/1250/1340/1380
Portland
 1190/1330/1640

>>Other than a noninductive resistor load, there really is no flat
transmit load anywhere. Antennas are different loads across a frequency
band, some worse than others. That's probably the main reason why some
stations are worse than others, and some don't run it at night. 
There is a limitation requirement for spurious signals. It's not
expected to be zero, but under a specific value depending how far off
the center frequency it is. Ever notice a second or third adjacent
station has some noise? Happens on FM as well. I have a local 93.3 with
IBOC. When they run that, I cannot hear a 92.7 station about 40 miles
away.<<

I have noticed IBOC hiss on frequencies there doesn't see to be a
station adjacent at night, especially off the Eastern beverage. However,
I know that the IBOC hiss can travel and if I do a bit a searching, I
find some 5 KWer running IBOC in the Midwent or East on an adjacent that
I probably am hearing. Too bad I cannot get the signal itself. A nice
new catch. hi. 
 
>Given the quick addition of internet access in new vehicles, IBOC will
probably be overrun by streaming audio. My personal guesstimate is that
when the streams are accessable by a significant percentage of people,
even transmitters may be less important. Think of the change from horses
to automobiles a hundred years ago...<<

I agree with you on that, I think that is coming. Especially in parts of
the country where electric rates are climbing. Is the 50KW transmitter
worth the cost to keep it running? The question is, will we be around by
then to take advantage of the cleaner radio dial? It seems many of these
stations are reluctant to drop the IBOC, even though there is no
adantage of keeping it especially on AM.  IBOC radios have never been
big sellers, even for FM. 

Patrick

Patrick Martin
Seaside OR 
KGED QSL Manager


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