Consider the baseband FM diagram below.
Do not confuse the abscissa with RF spectrum–this is baseband spectrum that is FM modulated before being transmitted on air.
Unfortunately even some technically-oriented websites get this basic and critical fact wrong.
Plain monaural broadcast FM as used prior to 1955/1961, and used wisely by some talk stations today instead of stereo to improve geographic coverage area by reduction of multipath interference, is frequency modulated audio from 50 Hz - 15 kHz.
FM multiplexing was employed in the early FM experiments by Armstrong, back to Nov. 1934 to send additional audio channels, faxes, etc. and
SCA became generally legal for broadcasters in 1955.
The April 1961 selection of the GE / Zenith FM stereo system chose a 19 kHz stereo pilot.
19 kHz is high enough above legacy monaural receivers low-pass filter response to not bother listeners.
88-108 MHz receiver, perhaps direct conversion RTL-SDR, assuming 960 ks/s
bandpass filter say ± 180 kHz before FM demodulation, to block adjacent stations while not making too much distortion. Remember the infinite sidebands of FM–don’t just clip to ± 75 kHz, it will sound badly distorted. OK to decimate down to 480 ks/s.
plain FM demodulation (differentiator) – do not use de-emphasis at this point.
frequency translate and low-pass filter SCA carrier e.g. -67 kHz shift, then low-pass filter 10 kHz or so.
FM demodulate this signal with 150 µs de-emphasis and decimate to sound card rate e.g. 48 ks/s
A normal baseband audio signal is emitted, if one was broadcast at this SCA frequency.
When connecting to multiple Windows PCs using
SSH port forwarding,
you might get error:
The host key for localhost has changed
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
Consider the security implications of option:
/cert-ignore
option in the freerdp command to bypass this error message.
Since the SSH server and RDP are both on the same Windows PC, the man-in-the-middle check may be somewhat less likely to be needed.
pathlib
is an object-oriented, Python standard library way to handle paths and filenames vs. “dumb” strings.
pathlib.Path() replaces most cumbersome code from os.path and glob.glob.
pathlib is standard library and supported throughout Python natively,
as well as in SciPy, Numpy, et al.
Eliminate messy os.path.join():
filename = pathlib.Path('mydir/a/b') / 'myfile'
Benchmark: pathlib is very efficient, for example with Python 3.6.2 and Ipython 6.1.0:
%timeit Path('~')
2.46 µs ±24.5 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit Path('~').expanduser()
7.35 µs ±7.13 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
Matlab
array size limit
attempts to stop the user from creating individual arrays that dig into swap memory.
Using swap memory is normally undesirable for data computations because the swap memory can be several orders of magnitude slower than RAM.
However, Matlab doesn’t check the total size of all arrays in the workspace, so the user must be mindful of
memory management
as in any programming language or data processing task.
The matlab-stdlib
ram_free
function tells the physical free RAM in bytes across operating systems for Matlab or GNU Octave.
If we assume the legacy incandescent lighting was 15 Watts each, that would be 32.9 kW of lighting on one carousel!
I think the incandescent lighting consumed more than 7 watts/light because that’s what old night lights consumed.
In any case, about 20 - 30 kW seems a reasonable estimate.
LED replacement for the carousel lighting would use about 10% of incandescent power, so nowadays that’s still 2-3 kW – more than an electric oven!
If we assume a 10 horsepower motor, that would be roughly 60 amps at 230 Vac single phase, for about 14 kW motor power.
So, an LED-retrofitted carousel might draw about 2 kW sitting still, and 16 kW while spinning.
If we assume 3 hours/day of lighted operation, and 6 hours/day spinning and $0.10/kW electric rate, then the electricity cost to run the carousel is estimated at.
(3 * 2 + 6 * 14) * 0.1 = $9.00 / day with LED lighting
(3 * 20 + 6 * 14) * 0.1 = $14.40 / day with incandescent lighting
However, one must consider the considerable labor cost of relamping the carousel.
Relamping labor is one of the considerable cost savings for commercial LED light upgrades.
Consider the cost of relamping on an incandescent Ferris wheel!
Two-way radio: Canobie Lake Park uses VHF (150 MHz) Motorola CP series portables.
GMRS repeaters on 462.550 and 462.575 (not park-related) were audible.
Because of the rural location and spread out nature of the park, simplex (direct) FRS/GMRS radios work well.
Canobie Lake Park’s maintenance of equipment made before the World Wars is impressive.
Several pieces were made by W.F. Mangels Co., of Coney Island, NY.
Running complicated Windows applications on Linux using WINE requires separate WINEPREFIX.
Each WINEPREFIX has unique Windows configuration, without disturbing the setup of other Windows programs on Linux.
This example is for Irfanview, a highly-useful image Windows viewer/editor that runs well on Linux.
Make the new wineprefix. You would make any special configuration in the GUI that pops up.
WINEPREFIX=~/.wine_irfanview winecfg
Install the winetricks prerequisites for your program. Here, Irfanview requires mfc42.
FlightAware has a
fork of dump1090
that uploads to the FlightAware network so you can contribute to the global flight database.
This can also run on Raspberry Pi or other Linux computer.
They have an optional inexpensive receiver with improved filtering and performance for ADS-B performance.
Before the emergency hits, get a $20 10,000 mAh or larger rechargeable USB power bank.
It’s possible to get 2-3 phone recharges from this bank for each recharge of the bank.
9V battery cell phone charge from 2014 has been disproved independently by the
Daily Mail.
A 9V battery has less than 100 mAh available at the 500-1000 mA charge rate demanded by modern smartphones.
This means the 9V battery current output quickly drops to near zero, while the phone still sees the input voltage, kicking the phone CPU into full power mode.
When a smartphone sees a 5V input on its charge connector, it thinks it’s on a source of adequate power, and starts checking email, syncing photos, putting the CPU into full power mode, etc.
Phones generally do NOT check if the charging source is actually adequate to have a net positive charge.
This means the phone battery will discharge faster by having a 9V battery connected via a cigarette lighter adapter.
Softlinks are useful on any operating system to replace long, complicated directory paths with a simpler one.
Options for accessing remote softlinked paths over SSHFS is best done with the sshfs -follow_symlinks option.
Example:
Server: joe@1.2.3.4 with external HDD /media/BigHDD
Microsoft removed 2gb152.exe (1MB) that was formerly at microsoft.com/en-us/download/details.aspx?id=12972.
CNet has msstdfmt.dll inside file 2gb152.exe at:
