Obnoxious, fatiguing artifact-laden codec. High costs. Self-
interference and analog noise. Adjacent-channel interference.
Encoding delay. Limited digital coverage. Necessitates drastically
reduced analog bandwidth. Won't work with a large percentage of
existing directional arrays. Engineers hate it; listeners couldn't
care less.

To these well-known HD-AM features we can now add: IBOC-AM can damage
power modules in the latest generation Harris 50kw transmitter, the
3DX-50.

There have now surfaced an increasing number of accounts - of course,
in typical HD fashion, being forcibly hushed by IBOC powers-that-be -
that the HD encoding and COFDM system can cause transient drive
failure to MOSFETS in the PA modules of the popular high-power Harris
AM transmitter being used by a large number of HD-equipped stations.
Result: PAs shut down, forcing reduced-power operation until an
engineer can make repairs.

There is at least one account of a 50kw midwest station that operates
its older-generation transmitter - that's right, a BACKUP - because
it's less susceptible to PA damage from HD encoding. Which of course
means that the shiny new 3DX-50 is relegated to the status of being
an expensive standby TX!

An unnamed source in the tech-support department at Broadcast
Electronics stated that he was truly thankful for HD Radio. Without
HD, the number of employees required to deal with technical problems
and issues would likely be halved.

I'd sure love to read the technical reports about exactly how the
damage occurred. I am assuming that maintaining flat phase in a
transmitter array over 50 kHz of spectrum would be difficult. But
with the digital sidebands only operating at 500 W, I'm a little
curious about how any realistic SWR mismatch at the extremes of the
bandwidth could return any more than a few watts back into the
MOSFETs.

If this can be documented, we should hear a lot more about it if they
boost the sideband power on AM! This could really turn the tide
against a return of investment on IBOC. I am wondering if it is the
reason why analog coverage is also lost, engineers are quietly
reducing the transmitter power just so they don't blow output stages

http://www.radio-info.com/smf/index.php?topic=94835.0

In article
,
IBOCcrock wrote:

Obnoxious, fatiguing artifact-laden codec. High costs. Self-
interference and analog noise. Adjacent-channel interference.
Encoding delay. Limited digital coverage. Necessitates drastically
reduced analog bandwidth. Won't work with a large percentage of
existing directional arrays. Engineers hate it; listeners couldn't
care less.

To these well-known HD-AM features we can now add: IBOC-AM can damage
power modules in the latest generation Harris 50kw transmitter, the
3DX-50.

There have now surfaced an increasing number of accounts - of course,
in typical HD fashion, being forcibly hushed by IBOC powers-that-be -
that the HD encoding and COFDM system can cause transient drive
failure to MOSFETS in the PA modules of the popular high-power Harris
AM transmitter being used by a large number of HD-equipped stations.
Result: PAs shut down, forcing reduced-power operation until an
engineer can make repairs.

There is at least one account of a 50kw midwest station that operates
its older-generation transmitter - that's right, a BACKUP - because
it's less susceptible to PA damage from HD encoding. Which of course
means that the shiny new 3DX-50 is relegated to the status of being
an expensive standby TX!

An unnamed source in the tech-support department at Broadcast
Electronics stated that he was truly thankful for HD Radio. Without
HD, the number of employees required to deal with technical problems
and issues would likely be halved.

I'd sure love to read the technical reports about exactly how the
damage occurred. I am assuming that maintaining flat phase in a
transmitter array over 50 kHz of spectrum would be difficult. But
with the digital sidebands only operating at 500 W, I'm a little
curious about how any realistic SWR mismatch at the extremes of the
bandwidth could return any more than a few watts back into the
MOSFETs.

If this can be documented, we should hear a lot more about it if they
boost the sideband power on AM! This could really turn the tide
against a return of investment on IBOC. I am wondering if it is the
reason why analog coverage is also lost, engineers are quietly
reducing the transmitter power just so they don't blow output stages

http://www.radio-info.com/smf/index.php?topic=94835.0

I can tell you that a transmitter in digital mode needs more headroom
than analog needs. Digital mode peak power requirements are steep.
Chance are the modules are being driven past their ratings and fail for
that reason after a while.

--
Telamon
Ventura, California