Doug Lung /
02.03.2011 12:00AM
NAB FASTROAD Announces VHF Mobile DTV Antenna Progress

The National Association of Broadcasters in a news release Improvements in Embedded Antennas for Broadcast Reception in Handheld Devices Unveiled described some recent work on more compact antennas for TV and FM reception.

The release provides little technical information on the devices or their performance, but said "New, embedded antenna designs, such as those developed under these FASTROAD projects, offer a much more attractive antenna solution to handheld device manufacturers than the headset cords or fragile, telescoping 'monopoles' currently in use. NAB and the antenna development partners encourage the use of these new designs by cellular handset and other portable device manufacturers for new radio and ATSC Mobile DTV receiver products."

You have to view the reports from Ethertronics and "The Technology Partnership" (TTP) linked to in the news release to get an idea of how these FASTROAD devices perform. The following is a short summary of the two reports:

The Ethertronics devices use a PC board with a zigzag trace and electronically tuned matching sections for low-band VHF, FM, high-band VHF and UHF. The Ethertronics – Embedded FM/TV Antenna System report offers some hope the technology will allow VHF reception with embedded antennas that's close to that available with whip antennas. FM band and high VHF peak "gain" varies from -12 to -7 dB. UHF "gain" varies from just under 0 dB to about 12 dB at 650 MHz.

No charts were provided for the demonstration board antenna at low-VHF frequencies. Given the small size of the antenna, these numbers must include the amplifier portion of the active antenna. Test results comparing whip antennas with the FASTROAD designs in a handheld ATSC Mobile DTV were encouraging, but I'm not sure the less than 2 dB advantage over a 10.5-inch external whip at low-band VHF frequencies above 76 MHz and a 4.5 dB disadvantage over the short whip at TV Ch. 2 will make low-band VHF DTV reception viable on mobile and portable devices. Even at UHF, the Ethertronics FASTROAD active antenna performs worse than a 10.5-inch external whip at frequencies below about 660 MHz (-4 dB at 470 MHz), although the compact size of the test antenna may justify the loss of sensitivity.

TTP took a different approach.

Noting the majority of TV tuners have separate VHF/UHF inputs and do not include an FM tuner, TTP designed two antennas, both requiring tuning with a varactor, for the VHF and UHF bands. The VHF antenna is a ferrite core active antenna, similar to the ferrite loaded designs you may have seen in the old Skytel pagers that used FM radio stations to provide nationwide coverage. The UHF antenna is made of stamped sheet metal.

The photos in the TTP report include the warning "photos depict antenna form factor but details are proprietary". Low VHF "gain" ranges from just under -31 dB to -25.5 dB. High VHF "gain" ranges from -20 dB to -17.2 dB. UHF gain varies from -1 dB around 600 MHz to less than -17 dB at 660 MHz. TTP did not compare its antennas to short whip antennas. Note that these VHF gains appear to be before the LNA.

These antennas offer the promise of better form factors--eliminating that pesky pull out (LG) or screw on (Samsung Moment test units) whip antenna--but they don't appear to provide enough of a performance boost, if any, to make low VHF viable for handheld and portable devices, even if the problem with noise from other electric/electronic devices is ignored. There isn't much hope at high-VHF either, at least with the Ethertronics antenna, which performed worse than a simulated 6- inch whip almost all high VHF frequencies.

Anyone who has played with portable TV sets (mobile or conventional ATSC) knows a 6-inch antenna doesn't work all that well on high VHF channels. TTP's ferrite loaded antenna for high-VHF may be a better performer. One thing that isn't captured in the gain numbers is narrow operating bandwidth of these antennas. They need to be electronically tuned and this may help reduce interference and intermodulation noise from strong out-of-band signals, such as those from non-adjacent channel white space devices. It would be interesting to see tests showing how the TTP antennas with LNA compare with the whip antennas currently used in ATSC Mobile DTV devices.

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Posted by: Brian Smith
Fri, 02-04-2011 - 1:23PM Report Comment
To quote Scotty, "I can't change the laws of physics!". It's all about aperture, capture area. Beyond a certain minimum aperture for a given wavelength, all those fancy fractal designs do no more good than a coathanger wire...and amplifying a noisy signal only makes more noise, kills the SNR. You don't learn these physical limitations by analyzing computer models, but by grabbing a coathanger wire and bending it up.

Wednesday 9:02AM
Analysts: TV Regs 'Not as Dire as We Thought'
We feel the negatives are known and are a lot more comfortable recommending the space.

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