The CGC Communicator Newsletter Web Posting

REGARDING THE PROPER IMPLEMENTATION OF HD AM

The following Letter to the Editor appeared in CGC #894:

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COMMENT ON HD RADIO

I am the Engineering Manager of a Los Angeles area AM &
FM combo and have nothing good to say about AM HD Radio and
little positive for FM HD.  The systems are seriously flawed
and cause a host of problems including serious adjacent channel
interference.  Fundamentally, HD Radio needs to be aborted, and
the last thing it needs is a power increase.

In its place, at least for FM, I'd deploy FMeXtra because
it's a good spectral neighbor and it's inexpensive.  It's time
we station engineers spoke up despite being muzzled.  HD Radio
is just plain bad science.

Name withheld upon request

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In reply:

Regarding HD and interference on AM, we recently installed a Nautel HD system with a new Nautel 50kW transmitter for a new, multi-tower AM array.  Based on participating with those who were involved in our installation, HD installations often begin to go wrong with the engineer doing the installation.  If that person doesn't fundamentally understand their entire antenna system, hasn't made all of the network measurements and adjustments necessary to even consider an installation, doesn't have the system FLAT (close enough doesn't work), and has older gear/short spaced towers, nearby AM transmitter sites that operate at close frequencies, hasn't created separate day and night settings, and/or hasn't done at least a few installations before, they are likely to have problems.

The consulting engineers (multiple) we used have been sent to several "legacy" 50kW sites to fix problems caused by staff engineers who think they understand, but actually don't understand, how to make HD play into their AM antennas.  Our site was built from the ground-up with HD in mind and we still had trouble with the night mask - and it varies by where you measure the signal.  In the end, though, it's been relayed to me that some very smart, very capable, well respected engineers out there are not as up to speed on HD as they believe they are.  And when it doesn't work for them, they trash the concept rather than take the time to understand the challenges inherent in their system (which is tough to appreciate unless they have a P.E. and are doing these things regularly, anyway).

It's like a surgeon.  If you're not using the surgeon who does the same operation 100 times each year, your odds of having a mistake increase with the surgeon who does it once each year.  HD implementation on AM is a surgical skill, not a general internal medicine skill.  Now, if people simply want to attack HD on the basis that implementation is complicated, and often difficult, particularly for AM, I would completely agree on that.  The people we worked with concede there are some AM arrays that would have to be completely rebuilt to make HD work.


Please withhold my information if you publish this.
March 2009

 

Posted by Steve Blodgett
Earthsignals.com