Johnythree

11 ms·

91.
by Johnythree 4y ago
You miss the point: Tesla chose not to fit AM radios because it would have made suppressing the electrical interference so much harder. Hopefully this will change as the FCC starts looking closer at the E.M. interference from Teslas.
92.
by Johnythree 4y ago
The various little radios based on the new Silicon Labs chips (Si4735 and similar) have an amazingly low current draw.
93.
by Johnythree 4y ago
The issue about AM being low quality is a bit misleading... In Europe the audio bandwidth of AM is almost the same as FM, especially with the BBC stations. And likewise in Australia, the gov ABC stations still transmit high quality audio on
94.
by Johnythree 4y ago
No. The maths show that AM can be received at much lower signal-to-noise ratios. And FM is intolerant of multipath reception which happens a on SW.
95.
by Johnythree 4y ago
The FM receiver that you linked to is actually an AM receiver, but it is using "slope Detection" to recover the audio. And FM is absolutely not "better" than AM. It does give a clearer signal on strong signals, but is de
96.
by Johnythree 4y ago
Most of the components are readily available on ebay today. It would be easy to build an exact duplicate and fire it up on one of the HF Amateur bands. In fact a number of groups specialise in recreating "Spy Radios" and getting t
97.
by Johnythree 4y ago
That is exactly what I am doing. The catch is that 4G data is horribly expensive in my area, download two youtube videos and you've blown a months Starlink fees.
98.
by Johnythree 4y ago
Except they were able to get phone lines into most of these "remote" places in the past.
99.
by Johnythree 4y ago
The problem with QPSK in particular is a loss of phase lock in marginal conditions, or with interference. It would require higher complexity, with no improvement for marginal signals. One possible improvement would be "Synchronous AM&q
100.
by Johnythree 4y ago
A PLL is one of the worst for phase noise. It will have a divider chain which will produce jitter and harmonics of the ref osc, and must absolutely rely on careful tuning of the AFC loop to null out these spurs. And as the filter will be di
101.
by Johnythree 4y ago
Aircraft use AM on VHF because it is still the most efficient mode. Unlike FM it doesn't suffer from the "Capture Effect" so you can tell if a weaker signal is trying to get through on a busy channel. And unlike FM it doesn&#
102.
by Johnythree 4y ago
Except that both can be true. A few millwats can reach across town, or across the world. The original claim was that "weak signals don't go very far", or some such.
103.
by Johnythree 4y ago
Yep, this was surprisingly common. When the picture tube in old B/W TVs lost emission, the EHT voltage increased to the point that it was constantly arcing and flashing over. But because the arcing was synchronised to the TV signal, it
104.
by Johnythree 4y ago
Nevertheless, the threat is to public safety communications. And not all Public safety use TDMA (or whatever). Aircraft communications is probably the most vulnerable, but so are HF/VHF marine operations, military and a host of others.
105.
by Johnythree 4y ago
Except this discussion is about possible interference across town, or even more locally. No need for "certain atmospheric conditions". The point was that very low power signals can go a long, long way.
106.
by Johnythree 4y ago
They also do it with very simple transmitters using perhaps just one transistor. All it takes is a few mill-watts and a reasonably efficient antenna.
107.
by Johnythree 4y ago
Any square-wave signal (eg PWM) will have spurs going up to UHF and possibly higher.
108.
by Johnythree 4y ago
I'm talking about the broad band of spectral components (both close in and further out) which are generated by the synthesizer. These are a separate issue to any sidebands generated by the modulation process. see https://en.
109.
by Johnythree 4y ago
It has nothing to do with Motoroa, TDMA, or 5G. If the wanted signal is very weak (eg from a distant aircraft using VHF AM), and there is an interfering signal on the same channel, the emergency communications will be distrupted.
110.
by Johnythree 4y ago
> "using some filters on the output" While it's relatively easy to remove harmonics, it is pretty much impossible to remove the broad comb of spurious signals either side of the carrier. Which why transmitters are not desi
111.
by Johnythree 4y ago
Until an angry Radio Inspector arrives on your doorstep having spent all day driving around your town with a spectrum analyzer to track you down. When you get to attend court, the judge will award the standard fines (and possible jail time)
112.
by Johnythree 4y ago
In my small town, local TV reception was being completely wiped out by interference. When the Radio Inspector came to check, he found a rechargeable torch sitting in it's charger bracket, which generated horrendous interference wheneve
113.
by Johnythree 4y ago
> when the broadcast doesn’t even make it through my walls. But you don't know. If it's radiating a few milliwatts (or even microwatts), that's sufficient signal to be hear across town in a sensitive receiver. The really s
114.
by Johnythree 4y ago
It's not so much "harmonics of the FM band", but the wide band of spurs either side of the transmission. The problem is that the unfiltered output of this device contains a wide range of spurs and harmonics which will radiate
115.
by Johnythree 4y ago
Radio Amateurs routinely communicate around the world with just a few milli-watts. And even a few micro-watts is sufficient to communicate across town. Many years ago the record was "1000 miles per milliwatt" using CW.
116.
by Johnythree 4y ago
If you are blocking an essential services channel (eg Aircraft, Police, Ambulance, military), the authorities can get a triangulation (within meters) on you in just a few minutes.
117.
by Johnythree 4y ago
A 20cm antenna will be a 1/4 wave at 375 MHZ (and a half wave at 188Mhz, etc), and thus will be a very efficient radiator at many different frequencies. Even a tiny signal can be enough to block the operation of a nearby police repeate
118.
by Johnythree 4y ago
I live in rural Australia and have never seen a QR code in a restaurant.
119.
by Johnythree 4y ago
Sadly, the .RA files are missing from that site. However you can download the broken file, (eg "lpl.ra") open it with a text editor, and extract the URL (eg http://home.att.net/~philys.la/lpl.ra ) And put that
120.
by Johnythree 4y ago
> I have been loving this site for old radio/electronics magazines: And many hundreds of books.

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