Listening to the Tech Guy podcast, I heard an interesting technical detail that changed my opinion about Aereo.
An expert friend of Leo’s suggested that it’s not physically possible for a single dime sized antenna (like Aereo was using) to properly receive* a signal in the frequencies used for television broadcasting, unless it’s very close to the broadcasting antenna.
Is this true? I seem to recall that CB and other antenna’s need to be at least a certain fraction (think 1/8th was the lowest) of the wavelength they’re trying to receive, so it makes sense that it’d be true for TV signals, at least for ones in the VHF band.
*technically the issue is that it’s too small to properly resonate with the appropriate frequencies
They did locate the antennas close to the transmitters. They are also electrically tuned to the selected channel, and so only need to capture a small frequency band.
you can add electronic components at the antenna that make it act as if it were physically a different length. there are limitations to what can be done.
a receive antenna with a very strong signal is accommodating.
I thought that as long as you had a conducting path that was comparable in length to the wavelength being received, that it didn’t matter how tightly coiled or folded the conducting path is. That that’s why modern chips are vulnerable to ElectroMagnetic Pulse- that individual circuits may be only nanometers wide but meters in overall length.
you can make long coiled of folded paths though it’s not the same as straight path. adjustments can be made to various degrees. compromises and adjustments and often something can work.
Antenna theory is horrid. EE students will complain it is one of the worst subjects. I’m not an EE, but there are a few points that can be made.
Antenna design is a mix of issues, and one is that you can’t divide the antenna from the feedline in any trivial way. All antennas have a characteristic impedance at any given frequency, and in order to get power in or out of it you need to match that frequency with the feed. Simple antennas (like half wave, or other fractional wavelength designs) are chosen partly because that results in a useful characteristic impedance. So that the antenna matches the feedline’s impedance.
A very tiny loop - or even just the end of a piece of coax does work as an antenna - just one with a stupid impedance, and thus one that it is very hard to get power in or out of. This doesn’t mean that you can’t make one work. If you built the receiver’s front end amplifier right onto the antenna, and appropriately set up the apparent impedance it would work. However that is only half the story.
The other one is that you still only get power out of the air proportional to the cross sectional area of the antenna. This is related to, but not identical to, the physical extent of the antenna. No matter what you do, a dime sized antenna will only grab dime sized amounts of power. But if you are close enough to the transmitter this may be enough.
I would be very interested to see a picture of Aereo’s antenna systems. Apparently they have a single antenna per DVR box, and thus one per customer. (This being their attempt to claim they are within the law - each entire leased DVR being a separate system - and thus within the private DVR rules.) What I would be interested to see is whether the arrays of little antennas are set up in a manner that creates a tuned array - ie one where the antennas are mutually coupled to one another - and maybe the whole thing is acting as a whole greater than the sum - with better directivity, and possibly less extreme impedance - and thus the antennas are not really acting in isolation, and it is really a single big antenna.
OTOH, the case went against them anyway, and looks really like an application of the duck rule. Which makes sense no matter what the technical niceties.
Francis Vaughan makes some good points. One thing that a lot of experts question about Aereo’s system is where does one antenna end and the other antennas begin? Maybe they are merely labeling a certain section of a large grid as being a given customer’s antenna but the whole grid together is needed to obtain a signal. Putting a bunch a leads all over the grid doesn’t mean each part is independent. Even if there isn’t a direct connection between parts of the grid, inductance can play a role as well as indirect connections via the leads.
It looks to me as though I am renting an antenna connection from them for $8.00 a month.
I take it there are only broadcast channels available. I’d hate to do without CNN, Sci Fi and Animal Planet.
The coin sized receiver can contain a coil which acts as an amplifier … The coil works a bit like an antenna but does not need to be the “wavelength size”. Anyway no antenna is needed… the receiver circuit measures the electrical field at the place…directly from its input… if that its from the air, from the cable from an antenna, then that is it.
The semiconductor is very good if it can pick up signal as low as -80dBm. Older circuits (eg vacuum tubes) were worse due to the capacitance of the circuits.
The semiconductor pickup cannot work if there is too much local noise… eg an analog TV with a CRT had the problem that the CRT operation was making noise that blocked the reception of signal… So thats why antenna is considered mandatory back then … Look at your GPS or phone ? no antenna these days… the coils work well for the frequencies in use…
Your roof top TV antenna is measured in dBi gain… such as 15 or 20 …
The Arecibo Observatory, Puerto Rico, which is huge, has a gain of 70 dBi , it multiplies the signal to be around 10 million times larger than than what a receiver with no antenna would receive … just as long as its not also amplifying noise.
They also provided a remote DVR service, so you could “record” and watch OTA broadcasts later. Of course, to be legit that had to make a separate recording of American Idol for each customer who wanted it.
