(You're not having deja vu; I've changed the date so this post appears at the top of the page.)

Hello, all!

For the first time, I will be in Las Vegas this year for NAB. I will be there with Luken Communications, who is exhibiting there for the first time this year, so my visit won't be the only first. =) I suspect I will be away from the booth much of the time, between meeting with vendors and trying to find people who I already know will be there.

Are there any users of RabbitEars who will be in Las Vegas for it? Can't promise anything regarding my availability outside of the show floor, but I would love to meet many people, both those who use RabbitEars and those who send me the data and updates that make RabbitEars possible.

I am very much looking forward to this show!

EDIT: One important note, for those who may not know me too well, the name "Trip Ericson" is a pseudonym. Confusingly, Luken Communications has hired a new Director of Sales, who will be at NAB, whose real name actually is Tripp. My real first name is Mark, and as such if you come to the booth looking for me, that is who to ask for, not "Trip." I hope to have a RabbitEars button or tag to pin to my shirt in time for NAB which should make me easier to identify.

I know this really isn't relevant to RabbitEars overall, but it's tangentially related in that it's about spectrum policy. I am sick to death of reading stories about LightSquared that do not address the technical issues. I want to republish a post I made on ArsTechnica yesterday to explain the physics of the situation to any who may not know, which seems to be just about everyone who reads these stories because they tend to be so poorly written. Here's a link to the original comment.

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The interference problem is due to the laws of physics, which is, in fact, why spectrum next to the GPS band is set aside specifically for satellite usage.

There is no such thing as a perfect filter. You can achieve certain amounts of roll-off over certain amounts of spectrum, but never reach zero outside the pass-band. You have to make trade-offs between the width and sharpness of the filter and the amount of signal the filter ultimately passes through.

Since GPS does not use a high-gain parabolic dish antenna like a satellite TV service would, the receiver needs to be able to gather as much signal as possible. A filter that doesn't have as sharp of a roll-off allows more signal to be passed through in the pass-band to the receiver circuitry, and so the FCC purposely put only other satellite transmissions in the adjacent bands. This means that since adjacent signals are going to be roughly the same strength (0 dB difference), the filter does not have to be as sharp, allowing as much signal as possible through.

Now, LightSquared wants to put a signal on the adjacent band that is about 130 dB stronger than what the FCC allows. And remember, that's not a linear scale, that means that the LightSquared signal would be 10^13 times more powerful than GPS. Not only are the filters in GPS completely unsuited for that, I don't think you can make a filter that will work for that in the size profile of a typical GPS.

My experience with filters comes from the TV broadcast industry. In US digital TV broadcast, before a signal goes from a transmitter out to an antenna, it passes through a "mask filter." For a full-service TV broadcaster, the filter is required to have a 47 dB drop by 500 kHz from the edge of the channel, and a 110 dB drop by 6 MHz from the edge of the channel. The filter can be anywhere from the size of a microwave oven to the size of a hot water heater or a refrigerator, is very sensitive to changes in temperature and humidity, costs thousands of dollars, weighs tens or hundreds of pounds depending on size, and I don't even know what the insertion loss is on it. And that filter might or might not be sufficient to deal with just the interference from LightSquared's proposal, let alone the fact that you now need a parabolic dish to collect enough signal to get something usable to the receiver chip on the output of the filter. Now, of course, this TV filter is designed to handle huge amounts of power compared to the amount of power a received LightSquared signal will be, since this is coming right off the output of the transmitter, but it's to give you an idea of just what an expensive, professional filter is capable of.

So, how does one design a filter with 130 dB off roll-off over 15 MHz (LightSquared ends around 1559 MHz, GPS is at 1575 MHz) without making the filter large and heavy and/or having so much insertion loss that you now require every GPS device to have a motorized parabolic dish? More importantly, how is this inability to overcome the laws of physics the fault of the GPS industry, who built to the specifications the FCC provided them and which were, themselves, based on the laws of physics?

This is somewhat off-subject, but I'm so thoroughly amused.

My preferred AM/FM radio is my Sony XDR-S3HD. I currently have it hooked to my outdoor TV antenna, which is technically too small for proper FM use. But it definitely works for me, bringing me quite a number of FM stations.

What has me laughing is the fact that if I tune to 96.1, I hear a local translator that sounds pretty clear for about 5 seconds before the IBOC of WKLS-FM Atlanta kicks in. The WKLS IBOC feed is the only reliable Atlanta IBOC feed, with the others fading in and out, but I have yet to hear the analog of WKLS.

On a semi-related note, the big Chattanooga FMs from Signal Mountain, like WDEF, WDOD, and WSKZ, are all getting eaten by multipath, thus confirming my issues with the TV side of things to be caused by multipath.

RabbitEars.Info is a member of the Coalition for Free TV and Broadband. This coalition aims to protect the TV broadcast spectrum from being taken by the FCC for auction to wireless companies. Irwin Podhajser is chairman of the organization and has written this essay which I am reposting here unedited. (I really should at least fix the "smart quotes" but I'm extremely tired.)