At NAB in Las Vegas, solid state devices were predominant in
broadcast transmitters, except for the higher powers. There were many
UHF and VHF television and FM audio rigs from Italy, using LDMOS,
along with the big guys like Harris, Rhode and Schwarz, Thales, and
others. Water cooled pallets are becoming more popular with closed
loop heat exchangers provided. FM broadcast transmitters are going
through a change with linearity requirements for the new on band
digital signal (HD Radio). Continental had a 816 running at 20 kW or
so on the floor with digital and analog modulation going. I heard
that the price tradeoff point is somewhere around
At lower frequencies, medium wave is almost 100% solid state now. I
didn't see anything with plate modulation, but a lot of PDM and class
D still. Harris had their 50 kW digital transmitter, and BE
instroduced their new '4M' 50 kW transmitter, weighing in at 1100 lbs
and slighly larger than some older 1 kW tube rigs from the 1950s. It
uses RF PWM, not requiring a separate modulator to do AM. DSP made it
possible. Quite impressive to see 50 kW rig that can be moved with a
refrigerator dolly. It had no power transformer either. Eddystone
Radio is back from near death, with DMOS FM transmitters and MOSFET
MW rigs.
Tube companies didn't show a lot of change at lower frequencies,
CPI/Eimac did show the 4CM100,000G tetrode which has pyrolytic grids
and multiphase cooling. Looks like a tougher version of 4CW100,000E
series. Thales had a TH576 (550 kW SW) tube in their booth. But IOTs
were hot, for both HDTV via UHF transmitters (around 80 kW now) and
new L band IOTs for scientific apps.
Several companies (Telefunken and RIZ that I saw) showed DRM
modulators and had results of SW transmitters using this modulation
scheme.
Of course I only focused on RF systems in 2 days, but there were
132,000 attendees approximately, and HD video and supporting
technologies was a big part of the thousands of exhibitors. It was
impossible to see all of it.
I did pick up a nice NAB Tee shirt in day-glow colors "Caution: Radio
Frequency Radiation Levels" for myself and my stepson. I may make a
nurd of him yet.
73
John
K5PRO
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