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The Taylorator – All Your Frequencies Are Belong to Us

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Re: The Taylorator – All Your Frequencies Are Belong to Us

#61

Post by badc0ffee »

The CRT enthusiasts on Reddit would love something like this, but for analog TV channels.

Something that people ask occasionally is how to use their vintage TV's tuner to receive digital TV. But they don't want to tune it to channel 3 and then change the channel with a digital TV box; they actually want to change the channel with the old tuner. The current advice seems to be to spend $hundreds to get an analog CATV head-end, and a separate digital tuner for each channel, but I've never heard of anyone actually following through and doing that.

Re: The Taylorator – All Your Frequencies Are Belong to Us

#62

Post by PaulHoule »

myself248 wrote: post #54
buescher wrote: post #47

Earlier quoted context omitted.

If by "ridiculously tricky" you mean "requires specialized equipment and domain knowledge". Like say, skiing. With a cheapish Rigol spectrum analyzer and homebrew receive antennas and DIY wooden/pvc tripods you could probably do 3m open-air measurements to within 3dB of what you would measure in an anechoic chamber at a test laboratory if you were very careful. I can 100% assure you that is possible with a commercial…

You can absolutely hook an antenna to a spec-an, but how do you calibrate the result? I can get a power measurement of mV or dBm at the instrument input, but that's not how the regs are written. They're written as field strength in free space (microvolts per meter), which as I understand it, either requires a calibrated field probe, or a calibrated antenna. I'm sure there's a way to perform such calibrations from fir…

I have to admit that having a ham radio license that would be easy to take away is one reason why I wouldn't mess with anything questionable radio-wise.

I wonder though if you could trust the published specs of a commercial FM transmitter to calibrate a power meter on it from a distance of a mile or so...

Re: The Taylorator – All Your Frequencies Are Belong to Us

#63

Post by PaulHoule »

alibarber wrote: post #49
trod1234 wrote: post #23

Earlier quoted context omitted.

The main problem with this line of reasoning is that it neglects important parts defined elsewhere making it seem like this is legal when its not. IANAL, but I do hang out with a lot of hammies. You can't help but absorb a lot of technical stuff with them around. Like for example, https://www.fcc.gov/enforcement/areas/jammers It need not saturate the bands, you technically are in violation the moment a non-licensed e…

I hold a ham radio licence in a couple of countries, although what's happening here is far outside of the remit of ham operations. I'm pretty certain this is not legal in my locale, but I don't think the author of the article is making this out to be legal - and I don't think they should get in trouble for any of this publishing [assuming you're adressing them, not the commenter]. Perhaps the equivalent of a script k…

... reminds me of the times I've taken my HT to Southern Cal and heard things on the radio (in the ham band and elsewhere) that I haven't heard any place else, like the ham who would hold court on the repeater with background music.

Re: The Taylorator – All Your Frequencies Are Belong to Us

#66

Post by xanderlewis »

mrandish wrote: post #16
threeio wrote: post #9

Ham radio has gotten me into more devious activities than I'd like to admit... but that's half the fun of experimentation :) Well done :)

From phone phreaking 40 years ago to FPV RC, I've found it to be a good indicator you're focusing on interesting emerging technologies when fellow early adopters in your new hobby say "Technically, this isn't even illegal... yet."

Not even illegal. It’s the new not even wrong!

Re: The Taylorator – All Your Frequencies Are Belong to Us

#67

Post by JKCalhoun »

RobotToaster wrote: post #24
myself248 wrote: post #5

With some filtering on the output to knock down harmonics and aliasing noise, and as long as the power output is low enough, this could actually be legal in the US. IANAL, etc, but this is my understanding: It's actually ridiculously tricky to measure transmitter power output in the terms that the FCC regs are written in, but the rule of thumb is that, given the receiver sensitivity of a typical radio, if you lose th…

> if you lose the signal when you're more than 200 feet from the transmitter, you're probably in the clear. With the FCC maybe, but someone far worse will be interested, the RIAA. It's copyright infringement by illegal broadcast.

Small, low-power FM transmitters have been around even prior to Mr. Microphone. Hooking to your Hi-Fi so you can get your music on the radio in the garage is as old as Jarts.

Re: The Taylorator – All Your Frequencies Are Belong to Us

#68

Post by JKCalhoun »

thijson wrote: post #6

I remember going to the drive-in movie theater in the 80's. You had to tune your car radio to a specific frequency to hear the movie audio. If this device had existed back then, you wouldn't have needed to tune your car radio at all. I doubt the neighbors would have liked that though. As an aside, I remember being jealous of the neighbors because they got to watch all these movies for essentially free. The irony is t…

The fancy Christmas lights on houses that sync with music do the same — instructing passersby's to tune to such and such in their cars as they drive past.

Re: The Taylorator – All Your Frequencies Are Belong to Us

#69

Post by cbruns »

formerly_proven wrote: post #8

> I'm not convinced that I'm operating anywhere close to peak efficiency. There may be some huge DSP-specific shortcut that I'm overlooking - I'm certainly no expert. But the current code works well enough. Something along the lines of taking the FM at baseband, transform to frequency domain, copy result n times and shift the coefficients to the right indices, much wider ifft to RF should work, right?

The most efficient way is a filter bank technique. Key words to Google would be "reconstruction", "dechannelizer", "synthesis".

A power of two number (N) of equally spaced frequency channels can be efficiently combined using a short fir filter on each channel followed by an fft where one sample from each channel is input to the fft per frame. Then you get N samples of your output. There is a bit more nuance but the author's bandwidth and number of channels are trivial to handle with this method.

Since each channel is already assumed to be spaced in frequency, you are essentially already in the frequency domain and only so only one fft stage is required.

Re: The Taylorator – All Your Frequencies Are Belong to Us

#70

Post by amluto »

The algorithm is an amusing nerd snipe. I’m not a DSP expert, but…

The idea of transmitting lots of low-bit-rate signals on different evenly spaced subcarriers is quite popular. OFDM is an example of exactly this, and the computation scales just fine. The same trick ought to work: compute in frequency space. You know what frequency-space signal you want to send on each subcarrier, so assemble the output in frequency space and iFFT it. I bet it can be done genuinely OFDM-style using transform lengths calculated to get the subcarrier spacing right with some additional care to get the boundary conditions right (conventional OFDM has a guard interval and doesn’t even try to transmit a continuous signal).

If all the songs are the same, there’s a much nicer solution. If the complex amplitude of the modulated song is A(t) (that’s just I + i⋅Q), then two copies are:

A(t) + A(t) ⋅ e^(2πit⋅200kHz)

Lots of copies makes:

A(t) ⋅ [1 + e^(2πit⋅200kHz) + … + e^(2πitn⋅200kHz)]

where n is the number of copies. The thing on the right is a geometric series and can be summed algebraically. So all that’s left is to upsample A, and it doesn’t need to be done especially precisely.

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