Questions tagged [propagation]
Questions about RF propagation including measurements, beacons, modes (ionospheric, tropospheric, ground wave), etc.
113
questions
3
votes
2answers
79 views
What is really happening during RF ionospheric refraction?
We all know that the ionosphere — when charged — refracts RF energy, but why? In other words, what is actually occurring at a molecular level to cause radio waves to bend back to earth because of ...
9
votes
5answers
140 views
Practical limits to maintaining coherence in an HF channel
Lately I've been thinking about weak signal communication on HF. Very weak, like weaker than even WSPR could achieve.
It would be nice if one could simply take any existing modulation and slow it ...
0
votes
1answer
99 views
Vertical Antennas
I have just changed from a ground mounted Vertical antenna , to a MFJ-1796 Vertical antenna, due to not having big enough ground to bury as many verticals
as recommended. So far what I have found is ...
2
votes
1answer
34 views
Propagation Analysis with WSPR / RBN
I would like to analyze data from the Weak Signal Propagation Reporter (WSPR) and/or the Reverse Beacon Network to understand the propagation mode(s) of the recent welcome spate of CW and SSB contacts ...
2
votes
2answers
767 views
What is this burst transmission sequence across the entire band?
Fairly regularly on the 40m band I hear a quick blip of a tone, and when I look at the waterfall I see these brief transmissions all across the band that look like little dots. What is causing that?
5
votes
2answers
58 views
Propagation effects of noctilucent clouds
I know auroras are a propagation mode, but I was wondering with the recent outburst of noctilucent clouds (as reported on www.space.com) brings with it any interesting propagation modes, either on HF ...
2
votes
2answers
142 views
Restricted line-of-sight communication
Why do line of sight communication links have a restricted range for a given tower height? Is it only because of the Earth's Curvature?
5
votes
5answers
446 views
Loop antenna layout and radiation?
I've got, for the near term, limited resources to put up an HF antenna at my home. One of the options I can manage without excessive cost is a loop, which would enclose the house. I need to transmit ...
3
votes
3answers
136 views
Given the classical top down view, what does a bottom up view of RF waves look like?
Quote from Wikipedia, Photons: "Nevertheless, all semiclassical theories were refuted definitively in the 1970s and 1980s by photon-correlation experiments. Hence, Einstein's hypothesis that ...
3
votes
3answers
101 views
Line of sight from geographic/map data?
I have line of sight issues with repeaters I want/need to use (it's a repeater network my club uses). One of the options that might be available to me is to install a "passive repeater" in a location ...
2
votes
2answers
97 views
Is there a trick for reaching a repeater “through” terrain?
I live in a draw, well below local average ground level. There are two repeaters I want to be able to use (because they're in the network my club uses). One is in the 440 band, thirty miles away but ...
3
votes
1answer
175 views
How can I be sure I'm actually hitting the repeater?
I'm just starting to use 2m and 70cm bands, which normally use repeaters to extend range beyond a mile or two (limited mostly by line of sight, as I understand it).
When I'm at home, however, I'm not ...
4
votes
1answer
80 views
High-resolution GIS datasets of groundwave conductivity of the United States, besides the FCC?
The FCC publishes a map of estimated groundwave conductivity of the United States, but the resolution is quite low:
Are there any GIS datasets that include groundwave conductivity at a higher ...
3
votes
1answer
895 views
Where does the year 2019 fall in the sunspot cycle for HF propagation?
I am reposting this question about the year 2016 here. This is 2019.
Are we now at the good or bad portion of the 11 years cycle?
What effect are we seeing now?
How large (strong/deep) is the effect ...
7
votes
4answers
232 views
Better explanation for beyond-line-of-sight VHF signal reach than “lower curvature to radio waves”
I am currently studying for the Technician Exam and have come across an answer to a question I think is ridiculous. The question is:
Why do VHF/UHF signals usually travel somewhat farther than ...
5
votes
4answers
867 views
How far do radio waves travel?
I have read that radio waves just keep traveling but the signal gets weaker because of how the wave spreads. OK, I get this, but what confuses me is that satellites emit signals from space that our ...
5
votes
1answer
349 views
Why are the lower HF frequencies not working during winter day time?
Currently my location is Nepal. We use the ICOM f-7000 radios without the antenna tuner. We use the frequencies round about 5-9 MHz, for communication over distances between 150 and 400 km.
During ...
1
vote
1answer
76 views
Why does signal power drop every night?
I have been monitoring power of a P25 control channel (at about 850MHz). For awhile, 24 hours a day. I graphed the power over a couple of weeks and it is almost sinusoidal, decreasing significantly ...
5
votes
1answer
587 views
Do short waves pass through or reflect off concrete buildings?
I live in Moscow, Russia and use DIY indoor magnetic loop antennas to listen amateur radio. Recently I received quite strong signals from Italy (20m, IV3UTV) and Slovenia (40m, S51CK), both operators ...
1
vote
1answer
93 views
Is there any way in which elevation *does* affect medium frequency (AM radio) transmissions?
This is a followup to this question of mine. From reading the wiki article, I get that:
Radio waves at MF wavelengths propagate via ground waves and reflection from the ionosphere ( called skywaves)...
3
votes
2answers
294 views
Using approximate signal strength at a distance to estimate reception strength of a radio station
I have some historical data on radio stations, but unfortunately, the dataset only has these variables:
the power of the transmitter, in watts
the coordinates of the radio tower
Unfortunately, I don'...
1
vote
1answer
104 views
How is RF Power at Receive Antenna Output Terminals Calculated?
Is the Friis equation sufficient to make this calculation? Must other considerations also be evaluated?
1
vote
2answers
115 views
True near field distance for a short monopole antenna?
Antenna properties:
Height x Diameter = 3.3 inches x 1.4 inches
Test Frequency: 900 MHz
(Wavelength = 33 cm or 13 inches)
I see some conflicting formulas to calculate the near field distance for ...
1
vote
0answers
28 views
To decide coherent time and fade duration from measured received signal spectrum and relate them to channel modeling
This question was asked in Electrical Engineering 2 days ago but hasn't received very informative responses.
https://electronics.stackexchange.com/questions/387255/decide-coherent-time-and-fade-...
0
votes
3answers
199 views
Should Hams Using Skywaves Be Concerned About Their Groundwave Radiation?
Comments posted on various websites relating to amateur radio posit that the groundwave is unimportant for skywave paths. Is this concept correct?
4
votes
1answer
138 views
Two way ham radio to communicate between two stations
Apologies if this not the right place for this question.
I'm into electronics and now endeavouring into radios and communications.
Unfortunately I'm not sure what terms to use to find what I'm ...
0
votes
1answer
92 views
Does the E-field propagate faster that the H-field?
I need some proof that the electric (E-field) and the magnetic component (H-field) of a lightning stroke both propagate at the speed of light, and that there is not a significant delay between them.
...
1
vote
1answer
42 views
Is it correct to apply the log-distance path loss model for an in-body radio propagation?
The application is an implanted sensor and I am asked to characterize the transmission channel. I did measurements with bio-equivalent liquid and got a plot of the path loss over distance. The ...
3
votes
4answers
8k views
When will propagation on HF improve?
Will the propagation on the High Frequency bands come back up soon?? I am referring to the 3 to 30 MHz range.
7
votes
2answers
202 views
Communications : Ground wave propagation
I was studying ground wave propagation, my book writes the lines about it without explaining it. I really do not know any explanation for these queries coming in my mind. I've Googled it, and you will ...
1
vote
2answers
152 views
Can a Loop Antenna send and receive 10,000 miles away
Can we expect a Loop Antenna such as a Chameleon F-Loop Antenna transmit and receive from the USA's midwest to Australia on HF using an average 100 watt SSB transmitter and an average receiver?
If so,...
5
votes
2answers
215 views
How can Ground Penetrating Radar work?
I was reading about GPR devices recently.
Considering the operation frequency of these devices, how they can go that deep (up to 50 feet)? Normally you would only expect a Hz to KHz range signal to ...
7
votes
6answers
837 views
Can I talk 2 Meter VHF across the United States
Can I talk on 2 meters from the east coast to the west coast without using repeaters?
5
votes
2answers
245 views
How is it possible for an HF signal to go around the world when part of it must be in sunlight?
I believe most of us know about the ionosphere, and skywave propagation, but I'm kind of tripping up on the D-layer. If the ionospheric D-layer absorbs HF signals (40 meters, for example) during the ...
3
votes
2answers
138 views
Can you create a radio beam with a Faraday cage?
Imagine we have an isotropic antenna at the origin emitting a steady sine wave at frequency $f$. Encompassing the antenna is a sphere of radius $r$ made of a fine copper mesh (with holes $\ll\frac\...
3
votes
3answers
442 views
Why is VHF better than UHF in this situation?
One of the sample questions for the British foundation level test is:
An amateur has the choice of VHF or UHF for a particular contact of some 25km. Which statement below best describes his choice?
...
1
vote
2answers
529 views
Difference between Phase Velocity and Velocity of propagation in a transmission line
I'm confused by the difference between the phase velocity and transmission line propagation velocity
From https://en.wikipedia.org/wiki/Speed_of_electricity, in a good conductor, phase velocity (...
15
votes
7answers
8k views
What is the cause of this unusually long period of terrible HF band conditions?
I've been a ham for over 40 years, but never has there been such a prolonged period of such poor propagation. This has been especially the case over the past six months or so, and they continue to ...
5
votes
1answer
398 views
Does geology affect radio signals?
following on from an earlier question about Iron Ore affecting radio waves... are there any other geological properties that can affect radio waves?
Are certain frequencies more susceptible to ...
4
votes
1answer
436 views
Troposcatter: really all that bad?
The previous question,
Packet Radio at 100 miles
and specifically, Phil's answer raised an interesting question:
In a 50–100 km distance situation where Line-Of-Sight beams aren't an option for ...
1
vote
5answers
288 views
How to learn about the physics behind propagation?
What are good sources for information about the propagation of RF that details the equations behind the curtain?
I've been able to find some simple stuff on wikipedia but nothing fancy that I'm sure ...
9
votes
4answers
701 views
How does VHF/UHF propagate beyond the expected (radio) horizon?
I am not asking about the fairly well-known effect of the earth "appearing less curved to radio waves" that are otherwise still essentially line-of-sight, but a deeper arcanum:
In the ARRL Antenna ...
2
votes
2answers
233 views
(HF) How to maximize probability of successful transmit given constrained packet duration? [closed]
I need a HF link that will be (mostly hah) operational 24/365. Edit: at least at local daytime.
The link is supposed to transmit a controlling signal (just one bit) in one direction for quite a ...
0
votes
1answer
116 views
How to compute/simulate signal propagation latency?
I need to transmit small amounts of data (~5kb/s) in the fastest way possible over the distance around 2500 km.
What is the the best way to carry out such transmission?
How could I estimate or ...
3
votes
1answer
174 views
What is the best way to get propagation VHF map for FM repeater?
Is there a way to get a professional propagation map for my VHF 50 watt repeater?
4
votes
1answer
152 views
No stations on MW band at daytime
I have a portable radio which serves for FM / MW / SW bands. At nights I can listen to 4-6 international channels from different countries on MW. However, I am unable to tune them at daytime. Is it ...
8
votes
1answer
2k views
What's the difference between “maximum usable” and “critical” frequencies?
In discussing HF ionospheric propagation, you hear about both "critical" and "maximum usable" frequencies. For example:
Above the critical frequency, the ionosphere is unable to refract the signal ...
1
vote
0answers
46 views
Can two directional antennas be connected without an amplifier to improve reception? [duplicate]
Can two identical yagi antennas be linked together to improve a cell phone signal?
The idea is to put one antenna on the rooftop and the other in the house, and connect the two with feedline but no ...
5
votes
3answers
154 views
If EM waves require no medium, why can't I get service at all times?
I have taken two years of high school physics and am very interested in RF communication. I know that electromagnetic waves do not necessitate a medium in order to propagate. Thus, shouldn't I be able ...
6
votes
2answers
7k views
Where year 2016 falls in the sun spot cycle for HF propagation?
Are we now at the good or bad portion of the 11 years cycle? What effect are we seeing now? How large (strong/deep) is the effect during the peak and bottom of cycle? What will change in coming years?
