Not generally useful to show this by default, because nowadays most pages are dynamically generated and although it's technically easy to implement, the last modified header is typically not set to $now.
Well, if Browsers would show it more prominently, there were more motivation to think about it for developers.
But Browsers are bad HTTP clients. Think about bad user experience with file uploads (no built in progress report!?), HTTP auth (not showing status, no logout etc.)
In Chrome you can F12 and go to "Network" tab and then refresh the page. Choose the first file in the list (that's the HTML itself) and you will find "Response Headers" in the "Headers" panel, which includes Last-Modified. It's a bit deep, which makes sense as it's rarely useful.
The variation in local noise between different locations is huge. As an apartment dweller and radio amateur, this is something I am fighting every day and in a densely populated environment, the noise floor changes all the time, depending on which neighbor operates which electrical device at the time...
The amateur radio community is very aware of the problems and several initiatives have been launched to quantify the effects. One of them is the DARC's ENAMS, which is described in detail here:
Have you tried a QRM Eliminator? I haven't tried one myself yet, but I hear good things about them. Also, some really simple things can be really noisy. Cheap LED bulbs for example can be super noisy. I had one above my desk that was terrible.
I think that's a phasing device. You attach an auxiliary antenna specially to pick up the noise. The signal from that is phase shifted and mixed into the signal from the main antenna. The phase shift circuitry has knobs to vary the phase and amplitude. You adjust them so that the noise cancels out.
That can be effective but it's really only useful for cancelling out one noise source. I once used a similar device when there was something bad happening on a power pole down the street. It's no use if you have general noise from multiple directions.
A buddy of mine uses one and it is effective. Most of your noise will come from buck converters and other cheap power supplies in the near field. Cell phone chargers, 120ac to 12vdc PSU, computer PSU, and fluorescent lighting ballasts are big culprits. Plasma TVs will generate more noise as they age. Pole-mounted cable repeater PSU go bad and start heating up, generating a shitload of noise. Any arcing on cracked insulators will generate RFI and can be easily located by driving around with a clear AM channel on your car stereo. Report these as they must also be repaired. Cheap solar panel inverters are also noise generators. A process of isolating house circuits helps identify the offending devices if they are in the home. In most cases, it is unlawful for devices to generate spurious emissions. In the case of solar panel inverters, they must fix/replace them if you complain. Another thing to check is cable tv leakage, which is less of a problem today, but can still cause interference. Unterminated cable coax can radiate lots of noise in the 144mhz band, and also on other channels. Great article about RFI hunting and elimination: https://www.arrl.org/files/file/RFI/Thompson%20Noise.pdf
Setting a dangerous precedent, especially doing this by default (no opt-in) needed.
But then again, if the people who carelessly include 3rd party dependencies (i.e. playing with fire) are those who use CF... they probably won't object to it :-)
Typical FMCW radars transmit very short ramps (microseconds) at a very long (relatively) intervals (several ten milliseconds), i.e. a duty cycle of less than 0.1%.
In order to create interference between two radars, the ramps have to overlap pretty exactly, within a few nanoseconds of each other. This is very unlikely to happen.
Modern radars employ technologies to detect and/or avoid such collisions.
Overall it is not really an issue, even with many radars in crowded spaces.
This is true for some earlier lofi radars, but as driver assistance and self-driving have developed, so have the requirements and capabilities of the radar systems. Newer systems generally have shorter PRIs for higher doppler bandwidth, and much higher duty cycles for more energy on target - the FCC limits power, so you've got to get energy from the time axis. Both of these things make the interference problem harder.
In practice, the difference between pulsed radar and continuous wave radar is a continuum rather than a dichotomy. Historically, FMCW (frequency modulated continuous wave) had a high duty cycle (though not 100%, the ramp generators need finite time to reset (though you can alternate between up and downramps and get closer)). For some applications, though, requirements force you to short ramps and long PRIs, thus low duty cycles, but the name (FMCW) sticks.
I am running a few websites which have a simple feedback forms which POST to a simple PHP script that sends me an email.
By filtering for a few keywords, you can get of 99% of the form spam.
Deliverability has never been an issue for me since (of course) I run my own mail server.
But I doubt it's a serious issue when you take the little time it takes to set up DKIM etc.
I wouldn't make it more complicated than it has to be :-)
I agree, I even went the other way and removed the email notification and just kept an embedded SQLite database. I figured that's more reliable than hoping the emails always end up in my inbox.
This SDR won't be able to compete with expensive high performance receivers that have a lot of pre-selection, but there are many examples of low cost SDRs that do a surprisingly good job on the HF bands (without too much pre-selection).
I suppose the performance in the HF range will be similar to KiWiSDR, AirSpy, or the RedPitaya. If you want to know how well they work, there are many KiWiSDRs online to listen to :-)
The interesting part is certainly that it delivers 50 MHz bandwidth up to 6 GHz, which exceeds e.g. what the ADALM Pluto can do.
Certainly an interesting product at an attractive price tag. I consider getting one!
KiCad. It's very stable and offers features that some of the professional programs lack. Extensive part library built-in, and easy to extend. Under active development.
If you find "wave hunting" this interesting but don't have a SDR / receiver of your own, there are plenty of (free to use) WebSDRs to get started: http://websdr.org/
Not generally useful to show this by default, because nowadays most pages are dynamically generated and although it's technically easy to implement, the last modified header is typically not set to $now.