While that chip can tune the large frequency range, but what i the dynamic range and IP3 values for that chips ? The requirement for DVB-T reception is one thing but the requirement for a good quality general coverage receiver is an other matter.
Power electronics is needed only in truly variable sped windmills.
An asynchronous motor (induction motors) run about 1 to 5 % below synchronous speed.
When used as generator, you need to run the generator a few percent above synchronous speed. How much more, depends on the loading.
Some big windmills (in MW class) use async generators.
The problem with these generators that it can't alone start a black net.
The dynamic range is limited more by the 8-bit ADC than by the tuner chip. It sure is a low-end device but it usually performs better than low-end superhet designs of such wide bandwidth.
This function of the stick is not actually used for DVB-T but the same stick can also receive DAB and FM broadcast using its native software.
A wide selection of software exists that runs on this stick and does anything from NBFM, SSB, AM using many different "graphic SDR" programs to GPS and ADS-B and other specific transmissions.
Crappy receivers aren't interesting. I can build that out of stuff I have in my drawer plus a few coax cables.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I updated my 8 day spreadsheet and graph to show a 96 point moving average (24 hrs * 4 measurements/hr). You might be correct that the long average frequencies is off a little. Looking at Mar 02, 2018, it's down to 49.980Hz. At exactly
50 Hz, a line frequency counting clock would produce: 24 hr/day * 60 min/hr * 60 sec/min * 50 pulses/sec = 4.320*10^6 pulses/day At the average frequency of 49.980Hz, that would be: = 4.318*10^6 pulses/day therefore losing 2000 pulses per day. At 50 pulses/sec, that's a loss of 40 seconds per day, which is rather high. Of course, they could just increase the average daily frequency the next day by whatever is required to supply the missing 2000 pulses, which results in zero error over a 2 day period. Looking at my graph, that seems to be what is happening, but over a 3 day period (Mar 3 to 6).More: "Accuracy and stability of the 50 Hz mains frequency" "60 Hz AC Mains Frequency Accuracy Measurement"
Good luck on your project.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
this is a good formula to know... I presume SNR in the above formula is unit less? (and not dB)?
thanks
Mark
Yes--1e6 SNR means 0.7 1 microradian RMS.
The same formula works for fractional amplitude error, . You can derive them from the formula for the sums of sines and cosines and then take the RMS value. (It's only a few lines of algebra.)
The reason for the sqrt(1/2) is that half the noise power is in the I phase, which affects only the amplitude, and half is in the Q phase, which affects only the phase.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
The AC behaviour of ADCs can be pretty subtle, as is demonstrated by the near-universal failure of everybody's first try at a digital lock-in. ;)
The other thing is that communications is a surprisingly demanding application. Back in 1982-83 I did most of the time-and-frequency control electronics for the world's first civilian DBS system. The toughest was synthesizing the 112-117 MHz signal that was multiplied X120 to make the microwave carrier. The FM noise spec was 5 Hz RMS in the 5-100 Hz bandwidth around the 14 GHz carrier, so my spec was 42 dB tighter than that. Initially I had no idea how hard that was, but I eventually managed it.
That's not too hard to do--Parzen's book on XOs has a lot of good wisdom on that. The key iirc is to make the feedback network (the two caps in a Colpitts for example) look capacitive only at the overtone you want, and have gain too low for a low-Q LC resonance to oscillate. (It's been a long time since I designed an overtone crystal oscillator.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
It's worse than that. If there were slip, huge currents would flow between generators. In fact some generators are used for power factor correction but they're synchronous, too (but out of phase).
You could build a usable receiver with that chip with that kind of frequency range, by inserting octave filters in front of it. This would reduce spurious mixing products with LO harmonics. With octave filters, you can also attenuate the lower octaves so that the band noise is only slightly above the receiver own noise in each octave. The band noise increases significantly when going into lower frequencies, so if the same sensitivity is used on all bands, the band noise will swamp many of the least significant bits.
With proper analog front end filtering all this kind of demodulation can then be done in digital domain. Unfortunately, these octave filters do not fit into a USB stick.
When used for a specific purpose you normally put a bandfilter for that specific band in front of it. The fact that it has such a wide tuning range does not mean you have to let all that RF into it. Of course it is what will happen when you just use the stick and its small whip antenna, but you would normally dedicate such a stick to receiving an amateur band or similar and for that it works surprisingly well.
E.g. we can use it to receive the 144-146 MHz amateur band on a broadcast transmission tower where several FM radio programmes are transmitted at a couple of kilowatts RF output, the receive antenna being a couple of meters away from a layer of dipoles from the stacked dipole transmission antenna.
Of course in such environments you need a good bandfilter in front of it.
The more high-end SDR devices of course have the switchable filters and they work better when used in a typical environment (not on those towers, there those filters bring nothing). The DVB-T stick is only shown as an example how your $10 spent on such a thing brings you more performance than $10 spent on a superhet radio. At higher price points like $200 it will still be a similar situation, of course when you spend $2000 the difference will become less and less.
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