[opendtv] Re: DTV Delay Bill

If the change is relatively small, it is easy to change frequencies. An agile exciter can be tuned to another channel as easily as a television changes channels. If the final output stage is solid state, there's not much else needed. If the output stage is an IOT or MSDC Klystron, then the cavities also have to be tuned for the new frequency.
Then there is the harmonic filter and the ATSC mask filter that either needs to be retuned or replaced. That's not such an easy task.
And finally there is the waveguide and transmitting antenna. Certain waveguide segment lengths aren't compatible with certain frequencies, and if you have a slot antenna it is tuned for a single frequency and must be replaced. If you have a wideband panel antenna, then you can reuse it.
In our case the jump from 23 to 40 required gutting of everything from the IOT to the feedline. The old NTSC harmonic filter had to go, the switchless combiner had to go, even the waveguide from the output cavities had to be changed out.
Also, since we're going from NTSC to ATSC on this transmitter, the exciter and upconverter had to be changed out as well. I think our IPAs are staying. 

John
----- Original Message ----- From: <dan.grimes@xxxxxxxx> 
To: <opendtv@xxxxxxxxxxxxx>
Sent: Wednesday, January 28, 2009 11:37 AM
Subject: [opendtv] Re: DTV Delay Bill



How easy is it to change frequencies?  I thought that transmitters were
pretty much designed for one channel and weren't easily manipulated.  But
it sounds like they can be changed in a day these days.  I imagine with
new synthesized frequency generators, it is now programmable.  How do they
work these days?  Is the RF processing and transmission path able to
handle a wide spectrum?

Dan







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