Doug Lung /
RF Shorts - Aug. 17, 2012
A review of RF-related news over the past week.
FCC Frowns on DTV Channel 6 Analog Subcarrier Plan
Allaccess.com reports FCC Nixes Bid To Allow Analog FM Audio From Digital Channel 6 LPFMs
. Some operators of analog Channel 6 low-power TV stations have been using their stations as “Franken FMs” by increasing the deviation of the FM subcarrier and boosting its power. As the FM subcarrier is 87.75 MHz, it can be received on many FM radios. Venture Technologies Group LLC apparently sought to take advantage of this and filed applications to use Axcera's “Bandwidth Enchancement Technology” to reduce the bandwidth of the DTV signal and insert an FM subcarrier above the VSB DTV signal.
The Allaccess.com article includes this statement from the FCC letter denying the applications:
“…while VTG states that no interference will occur to other stations from its proposed facilities, the Commission has not adopted rules regarding engineering protection requirements for 'hybrid' analog/DTV stations to other DTV stations seeking to use Channel 6. At present, there are published D/U ratios for DTV-into-DTV and Analog-into-DTV co-channel operation which were developed from years of testing, but there are no D/U ratios for “hybrid”-into-DTV operation. We also note that on its face, VTG’s proposal is likely to increase the interference potential to co-channel DTV operations because VTG’s proposal would increase the total power of its channel 6 operations by 33 percent. Accordingly, this type of operation proposed by VTG may reduce the number of DTV stations that might operate on Channel 6 and/or reduce the populations served by those DTV stations."
It will be interesting to see how Venture Technologies responds to this. Will they submit a revised proposal, perhaps with lower power, and studies showing no new interference?
Maser Technology Breakthrough Announced
Before lasers, there were masers (maser is an acronym for Microwave Amplification by Simulated Emission of Radiation). The early devices were large and inefficient, producing only a few nanowatts of power. An article by Geoff Brumfiel on Nature.com describes a major advance in this technology.
Microwave laser fulfills 60 years of promise – Physicists build first practical maser
. The story behind the technology is as interesting as the technology itself. Mark Oxborrow, a physicist at the UK National Physical Laboratory in Teddington created the maser using a spare pentacene crystal he cooked with p-terphenyl to create a pink crystal a few centimeters long. A laser was then used to excite the pentacene molecules to a metastable state.
Microwave energy passing through the crystal causes the molecules to relax, releasing a cascade of microwaves of the same wavelength. Oxborrow said that he found the laser he used in the experiment on eBay.
According to Oxborrow the experiment succeeded on the first try.