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HF propagation over long distances is by skywave propagation, the reflection and refraction of radio waves between Earth's surface and the ionosphere. The ionosphere is a consequence of radiation from the sun ionizing Earth's atmosphere, so it changes significantly with time of day and sunspot activity.
Although time of day is just one of many variables, ...
19
Receive antennas are the easiest thing ever. You just need two things:
something that conducts electricity
another thing that conducts electricity
Attach one to the center contact on a BNC connector. Connect another to the shield. Boom, done. If you can't find two things, then one can be the Earth.
Alternately, you can use two ends of one thing that ...
19
CW signals are not “transmitted on the upper sideband”, nor the lower one. A CW signal is approximately at a single frequency (with only the additional bandwidth required to allow the key-up and key-down transitions).
However, the standard method of receiving a CW signal is identical in structure to a single-sideband receiver. The local oscillator (LO) of ...
18
You are going to have a very difficult time achieving the first 4 with any band on a low budget. But in general, I'll say a few words to get you started.
You probably want to be able to use digital modes. Your best bet to get consistently across the country will be via digital modes, as they can add something like 20-30 dB effectively to your signal. Olivia ...
18
Amateur Radio operators use this rule of thumb for historical technical reasons. SM0AOM on the QRZ forums writes:
The changing of ISB sideband positions at 10 MHz actually has an engineering background.
In the earliest ISB exciters, it was found appropriate to change the final mixer scheme from subtraction to
addition mixing at around 10 MHz due to ...
17
First, I'd be sure it's actually the antenna picking up the noise, and not something else. If you don't have a balun on that dipole, probably your feedline is picking up all the noise in your house.
Any other wires attached to your receiver can also make good noise antennas, especially the power cord, which is attached to your home's wiring, and coupled to ...
15
Some types of noise are very short bursts of energy. Car ignition noise is one example. Power-line noise caused by switching triacs in light dimmers is another. For example, see the top image here:
(source: A Line-Synchronous Noise Blanker by KA7OEI)
This image also illustrates the effect of band-pass filtering on these pulses. The middle image shows the ...
15
In general, the shorter wavelength HF bands are better during the day, and the longer wavelength ones at night. Although that depends a bit on what you want to do, and like all things propagation, it's subject to change. Let me try and give a rough mode of operations. Also take a look at the chart from eham.
6m- Randomly opened, in random directions. I ...
15
I have a scanner capable of HF receive, multiple HF receivers, and several HF SDR transceivers capable of receiving on more than one amateur band slice simultaneously. Lots of contest stations run more than one receiver at a time to "pounce" on whoever pops up on any of several bands.
When using a radio with a scanner, or a station with multiple ...
14
You may be surprised to hear this, but the antenna you describe isn't actually a vertical, but a dipole. One half of the dipole is the IMax-2000, and the other half is your feedline.
You can not simply not have radials and still have an antenna. An antenna works by making EM fields between two things. A dipole has two halves. A vertical works because the ...
13
A pure tone is an unmodulated signal — it carries no data. Almost nobody intentionally transmits a pure tone — it would be wasteful. The exceptions are the time-and-frequency reference signals like WWV, but they have modulated time information in addition to the carrier which serves as a frequency reference signal.
What you are receiving is almost certainly ...
13
It looks like a fibre or telephone cable strung between buildings.
It sets a good precedent for setting up your antenna though - if you can get access to the other rooftop at night, and a catapault or fishing rod. Make it fairly official-looking, with some large bolts and a labels with bar codes and lots of numbers.
12
It doesn't sound like you're doing anything wrong. Most likely, you are simply only hearing strong stations; broadcasters put much more power into their transmissions than amateurs are legally allowed to, so you can hear them over a much wider range.
Advice on the practice of listening:
For finding signals, first of all, always use SSB. Even if it's the ...
12
HF propagation is not only limited by manmade interference but also by natural phenomena like sunstorms.
Anyway, I'd account that to social and technological reasons:
HF activity suffers very much from the old men's club's image phenomenon (a term that I just invented!): How attractive is it to join a communication group that consists of old men?
Old men ...
11
So you want to broadcast your location using backpack-portable equipment from deep in a narrow valley hundreds of miles from civilization. I'll assume that you would also like the ability to get a message out when necessary. These are very demanding requirements. I don't think that there is any inexpensive, 100% reliable way to do what you seem to want, ...
11
It may have served a purpose in the past, with less filtering in transmitters and receivers, no digital frequency displays &c, e.g. to avoid mistaking a harmonic on a higher band for the transmitted signal.
10
Yes, a random wire can be a practical antenna. Anything conductive can be loaded up. Somethings work better than others. But if you want to play around, there's no reason the antenna has to be an "antenna".
There are, of course, some drawbacks:
You must have a tuner.
You might not get a match on every band you'd like to work.
For efficiency, you need a ...
10
Satellites can and do use HF for communications.
The first example would of course be Sputnik, which transmitted at 20 and 40 MHz.
Amateurs use HF to communicate with satellites. According to Amsat,
mode A: This mode requires a 2 meter SSB/CW transmitter and a 10 meter SSB/CW receiver...
Mode K; This mode requires a 15 meter SSB/CW transmitter and a 10 ...
10
The usual figure used in this context is, apparently, fractional bandwidth, defined as the bandwidth divided by the center frequency, and therefore having a range of 0 to 2.
$$
\text{fractional bandwidth}
\,=\, \frac{f_{\text{max}} - f_{\text{min}}}{f_{\text{center}}}
\,=\, 2\frac{f_{\text{max}} - f_{\text{min}}}{f_{\text{max}} + f_{\text{min}}}
$$
Given ...
10
The antenna itself won't be significantly affected by the water.
However, waterproofing the coax connection is essential. If this is not done, water will creep inside the coax by capillary action and ruin the coax.
There are several products that can be used, for some examples see 3M's application guide. However all have three elements:
An underlying ...
10
Intersymbol Interference (ISI) — or analog equivalents, like ghosting — are relevant only when the difference in time of arrival between the primary and reflected signal are significant compared to the symbol duration.
For example, PSK 31 has a symbol rate of 31.25 baud, meaning each symbol is 32 ms long. If the difference in arrival time is significantly ...
10
To send a message of around three bytes over such a long distance, would this require an antenna that uses alot of power?
No. There's a huge variety of tradeoffs here, but as a quick calibration, WSPR sends 50 bit messages (so, a bit more than twice what you're asking) all around the world using power levels usually ranging from several milliwatts to ten ...
9
The first thing to realize is that you can't make anyone move. So you can contact him and tell him (politely) the frequency was in use and he's interfering with you. At that point he may apologize and QSY. Yes, that does work, I have seen it happen. Or he'll tell you to pound sand or just plain ignore you.
If that happens, there is really nothing to be ...
9
The results depend on the two bands you choose. Frequency ratios of 2:1 are a good choice because the longer dipole, which is a full wavelength at the higher frequency band, will show high impedance on that band, while the shorter dipole, which is only a quarter wavelength at the lower frequency band, will show a high (capacitive) impedance on that band.
...
9
Your question seems as much about psychology as much as technical concerns. We mainly favor the technical questions, but I'll take a stab at the psychological aspects also. All of you, please feel free to disagree with my conclusions!
Coaxial cable is fairly inexpensive for many, compared to our time, even for LMR400. (Your mileage may vary.) For many, ...
9
Apart from historical reasons it's also a filler. When calling CQ on SSB you probably want to stretch out your transmission a bit because that's what you need to get heard. In theory you could just say your Callsign and "CQ", as it is enough information. If people would hear each call immediately it would suffice. In practise expanding the length ...
8
One strategy is to camp a frequency starting before the contest. No, those QSOs don't count for the contest, but it lets you get into the rhythm of things and shake down any issues with your setup before the clock starts running. Lots of contesters do this and you might pick up some DX while running like that.
In multi-band contests, one strategy is to ...
8
The maps are related, but as this excellent posting describes:
The 'critical frequency' is the highest frequency that gets reflected
when it is aimed straight up at the ionosphere.
However:
…as the angle decreases from vertical the reflected frequency increases.
And so therefore:
MUF or MOF is a path dependent value. It depends not only on the ...
8
Why aren't there monolithic HF ICs.
There are, in the shape of actual (broadcast) AM receiver ICs, which can most likely with minimal effort be also used to transmit.
However, are there technical reasons we don't see monolithic HF ICs?
Your market considerations are something I'd very much agree with. Why build a monolithic IC for something that is ...
8
The concrete is relatively transparent to radio waves of such large wavelengths (it attenuates, it doesn't reflect). However, steel bars within concrete typically convert that concrete to a solid reflector from the perspective of a wave with such a large wavelength.
Basically, that effect scales: Just as your microwave oven's front door has a metal plate ...
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