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1500 questions
8
votes
3 answers
Vertical antenna on HF?
What are some of the advantages and disadvantages of using a vertical antenna on high frequency? Are there any better antenna types that I should use?
Timtech
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8
votes
1 answer
What does CQ NM mean in FT8?
I saw someone on 20m FT8 this morning calling "CQ NM". What does NM mean in this context? They followed the NM with their call and grid as usual.
vegadoom
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8
votes
2 answers
dBm signal minus dB
I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm?
I've tried Googling that without any luck.
Chris Pavey
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8
votes
3 answers
Can I use a helical ground plane radial in the same way that a loading coil works?
I'm working out the science behind mounting an antenna on a vehicle, and I came across the concept of ground planes. This answer says that longer is better but don't worry about it too much, but this article focuses on 1/4 wave ground planes, as do…
YetAnotherRandomUser
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8
votes
2 answers
How to derive antenna gain from radiation pattern
I need to calculate the antenna gain in both dimensions: azimuth and elevation.
The datasheet of the antennas I am using has two different radiation patterns, one for the elevation and one for the azimuth.
Given the two angles I can derive 2…
gabriel-shatana
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8
votes
2 answers
What is inside a 50 ohm termination?
I see RF applications requiring 50 ohm termination to avoid any open port reflections. Curious what is actually inside a 50 ohm termination connector. Is it simply a 50 ohm resistor? But then it is rated for certain frequency range, so makes me…
eecs
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8
votes
4 answers
How can the voltage at the center of a resonant half wave dipole be zero if the input impedance is 75 ohms?
If the input impedance of a resonant half wave dipole at the feed point is 75 + j0 ohms, then if an AC sine wave voltage V is applied to the feed point, how can the voltage at the center be zero ? Ohms law always applies correct ? So for the rms…
Andrew
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8
votes
3 answers
It it really useful to terminate unused 75Ω outputs on a coax splitter?
When discussing improvements to my home HDTV Antenna/distribution system a colleague brought up the need to terminate all coax, even unused splitter ports.
My understanding of the way terminator works is that they prevent wave reflection, which can…
Thomas Guyot-Sionnest
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8
votes
3 answers
What exactly is a "balanced modulator"?
While studying for his U.S. General class license, my son wondered about the "balanced modulator" referred to by a few questions in the FCC pool.
Quoting KB6NU's General Class study guide to give a sense of the two questions:
Filters are also used…
natevw - AF7TB
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8
votes
2 answers
Is this a broadcasting antenna?
We bought an old house and found an antenna inside the attic of the house. I don't know much about antennas or radio but searching in Google I found a similarly shaped one and it describes it as a broadcasting one. Is that what this antenna is? If…
Wilreyca
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8
votes
2 answers
What's an appropriate core material for a loopstick antenna?
A loopstick antenna, if you don't know, is a coil of many turns around a high permeability core. They are frequently encountered in AM receivers and look like this:
This particular example is actually two antennas on one core.
What type of material…
Phil Frost - W8II
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8
votes
1 answer
What is the logic behind RG cable codes
What is the logic behind the names of different RG cables? The Wikipedia's Coaxial cable page has a list of different coaxial cable standards but I cannot find the internal logic of the naming. I would assume that coding pretty much anything would…
OH2FXN
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8
votes
1 answer
How do I maintain my frequency during a contest?
Suppose I am operating a busy HF contest, and I have found an open frequency to call CQ. I make a number of contacts, and then suddenly another station starts to call CQ right on top of me. The other station is either matching my frequency or within…
W5VO
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8
votes
1 answer
Is there a practical way for hams to participate in cellular-related technology advances?
My understanding is that there used to be more timely overlap between commercial and amateur radio technology — e.g. helping study ionospheric propagation, relatively early adoption of SSB technology, up through re-purposing business equipment for…
natevw - AF7TB
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8
votes
2 answers
How were 1920s hams able to measure megahertz frequency?
I was reading 200 Meters and Down but one thing that was unclear to me was that hams in the 1920s were operating on the 200 meter frequency, which is around 1.5 Mhz .... or 1500 kilocycles to use the old phrasing.
What's unclear to me is how they…
RoboKaren
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