Questions about RF propagation including measurements, beacons, modes (ionospheric, tropospheric, ground wave), etc.
1
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1answer
86 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
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2answers
68 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
27 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
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3answers
181 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
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1answer
95 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
80 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
29 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 ...
1
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3answers
961 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.
3
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1answer
96 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
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2answers
110 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
125 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 ...
6
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6answers
262 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?
4
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2answers
156 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
108 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
217 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
293 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 (...
14
votes
4answers
3k 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 ...
4
votes
1answer
226 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 ...
5
votes
1answer
238 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
213 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 ...
5
votes
2answers
280 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
210 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
100 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 ...
2
votes
1answer
132 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
133 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 ...
7
votes
1answer
1k 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
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0answers
40 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 ...
4
votes
3answers
147 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
4k views
Where year 2018 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?
3
votes
1answer
58 views
What causes the audio distortion when working aurora?
I recently watched a video of someone making an auroral voice contact, and the received audio had a distinctively raspy and disembodied sound to it. Some CW was audible in the background and it had ...
3
votes
2answers
204 views
What is “Meter” referencing in “60-Meter Band”?
I know that there are various bands referenced in meters (or cm). My question refers to what exactly the word "meter" is referring to when identifying the 5MHz band? I know that the 60-meter band is ...
5
votes
4answers
3k views
What is propagation like when there are no sunspots?
Am considering getting my license again after raising kids, and wondering if there is any point in HF operation besides local chats — that is, what is propagation like when there are no sunspots?
5
votes
2answers
289 views
Incoming angle of radio signal reflected off of ionosphere
I am about 870 miles and 16 degrees due west of WWVB at Ft. Collins, CO. WWVB transmits at a frequency of 60 KHz. At this distance I should be getting the signal reflected from the ionosphere. If I ...
2
votes
1answer
135 views
How do I simulate a receiving antenna in EZNEC simulation tool?
I have a situation where I need to find receiving antenna impedance when it’s $\lambda/2$ distance from the transmitting antenna. Both are dipole antennas. Is it possible with EZNEC?
4
votes
1answer
189 views
How far the near-field reactive region extends from the transmitting antenna?
I am doing research on near-field harvesting. In my situation the transmitting antenna is a dipole antenna operating at 2.45 GHz and its length is 14 cm long. I am trying to find how far near-field ...
3
votes
2answers
220 views
Acceptable link margin for voice communication in uhf band
I want to understand the theory behind how link margin or fade margin is decided? If I have to have a point to point UHF voice communication link from ground to aircraft, for example, with a ...
2
votes
2answers
149 views
Can RF work while it's in motion?
I have a project idea. It uses a pair of RF transmitter and receiver. The application is a little complicated since it involves motion, typically the speed of a vehicle going on local or even better ...
5
votes
1answer
184 views
Does a low amount of atmospheric noise reliably indicate a lack of propagation?
We know that the primary source of interference at HF is atmospheric noise. Thus, all else being equal, the strength of heard noise is a fair indicator of RX system performance (such as in adjusting ...
3
votes
3answers
944 views
Why did I lose my FM radio signal?
My lady and I were driving on the interstate recently when we noticed an unusual phenomenon. We were listening to the radio (an FM signal), and only over a couple of bridges did we entirely lose our ...
6
votes
2answers
434 views
Can there be (long range) propagation of HF from satellites?
HF transmissions from the ground can be reflected by the ionosphere leading to very long distance propagation. Satellites in low Earth orbit (160 km to 2,000 km) fly within the ionosphere (60 km to ...
6
votes
4answers
887 views
Why can't VHF / UHF be used with ionosphere reflection?
HF radio can be reflected by the ionosphere, giving very long range communications.
Why can't VHF / UHF used with ionosphere reflection?
Is it due to the attenuation of the atmosphere over that ...
3
votes
0answers
71 views
Calculating effective SSN (sunspot number)?
I am doing research on how SSN-like parameters affect HF radio signals. As I can see, effective SSN is a parameter that is derived from SSN or using other parameters. Does anyone know how to calculate ...
3
votes
4answers
2k views
What does multi-path sound like on FM?
I know I have probably experienced multi-path propagation on FM modes when I was working a repeater in the grand canyon and in the mountains. How can I identify when I am getting multi-path, and what ...
2
votes
1answer
469 views
What determines the optimum frequency range for the transmission of signals?
What determines the optimum frequency range for the transmission of signals in a system that's transmitting electromagnetic signals between an antenna on the surface of the earth and an orbiting ...
0
votes
1answer
250 views
What are the signal loss mechanisms between a ground station antenna and a satellite receiver?
What are ALL the potential signal loss mechanisms between the output of the earth station antenna and the input of the satellite receiver. With a bit of explanation for each if possible please.
1
vote
0answers
50 views
Interpreting the Friis transmission equation [duplicate]
In the Friis transmission equation, can you please explain the significance of the factor
$$\left(\frac{\lambda}{4\pi R}\right)$$
and what it helps us achieve? Specifically in terms of path loss.
2
votes
3answers
338 views
Should I use ham or cb radio? [closed]
I've been scouring the internet for the answer and my question is never directly answered, usually there is a bunch of technical jargon. It is not that I am unwilling to learn, because I want to, but ...
13
votes
2answers
2k views
Is free space path loss dependent on frequency?
Free space path loss is calculated as:
$$ \left( 4 \pi df \over c \right)^2 $$
The presence of $f$ in this equation means that losses increase with increasing frequency, so there's an inherent ...
4
votes
1answer
677 views
Why does the ionosphere reflect some frequencies and not others?
Why is it that some frequencies transmitted at some known direction are reflected back to earth, yet others transmitted at the same direction, power and polarity pass through into space with no ...
3
votes
2answers
151 views
Setting up an HF Schedule
I want to make a contact with a ham who is far away (>10,000km). How would I intelligently plan a scheduled contact to maximize possible success?
Assumptions:
Both stations have optimized their ...
