FCC approves nighttime IBOC for AM

[Aaron Read]

 >Larry Weil kc1ih@mac.com
 >Fri Mar 23 14:48:25 EST 2007
 >(snip)
 >The problem is so bad that my tuner will not show HD at all for WUMB, 
 >nor for WNEF.  When I aim at WNEF, WUML is a bit stronger than WNEF. 
 >Yet I am able to get HD and HD-2 on WFCR which is much weaker but the 
 >adjacent channels are clear.

Well, that tells you how often WBMT 88.3 Topsfield is on the air.   :-)

I admit I find this report confusing, but it can be "explained away" to 
some degree by WFCR's mammoth signal.  Plus we'll all need to get used 
to stations not coming in as well (or some coming in better) than we're 
used to with HD Radio since the propagation characteristics are 
noticeably different.

Just last night I was test-driving a new HD Radio receiver and quickly 
confirmed that I couldn't get WUMB's HD signal anywhere in Brookline, 
Brighton or Storrow Drive except for those parts (rather roughly) within 
their 60dBu contour...which cuts through those areas.

http://www.radio-locator.com/cgi-bin/pat?call=WUMB&service=FM&status=L&hours=U

Now obviously WFCR's 60dBu is over 40 miles away from Larry...but they 
also have 130 watts of HD Radio at 1500ft. AMSL, compared to WUMB's ~7 
watts of HD at 290ft AMSL.  Doesn't take much terrain to knock down 7 
watts into the noise floor.   And yes, adjacent channels sure don't help.

Still, I'm kinda surprised you can get WFCR HD from that far away. 
That's a good catch.

As for WUML and WNEF...contour-wise they should be about the same signal 
strength in the Marblehead area, with WNEF slightly stronger.  But both 
should be pretty weak.  And remember, WNEF is almost entirely vertically 
polarized so if you're using a horizontal antenna it's going to show 
some attenuation from that...possibly as much as -6dB (significant at 
that range).    There could also be a terrain issue that's letting a lot 
more of WUML over WNEF into your area...I'd need to do some Longley-Rice 
plots to check.

What tuner are you using, too?   Several of the home tuners have been 
(sometimes justifiably) accused of being rather "deaf".   If the tuner's 
not as good at filtering out adjacent channel interference it's not 
going to get WUMB cleanly on analog or digital.

-- 


--------------------------
Aaron Read
readaaron@friedbagels.com
Boston, MA 02446-2204