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1500 questions
21
votes
3 answers
Why do I need to tune an antenna?
I've heard that when an antenna is set up, it needs to be tuned to reduce reflective power back into the radio. Is this always necessary, and if so how would I go about tuning it?
berry120
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21
votes
6 answers
What's the difference between saying “CQ” or “QRZ” in a contest?
I'm listening to (or let's say I'm trying to participate in) a contest (or perhaps Field Day), using SSB.
I noticed that a station would, after completing a contact, sometimes say “CQ” and sometimes say “QRZ”. In either case, other stations then…
Kevin Reid AG6YO
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21
votes
2 answers
How do I make a RF propagation map for a repeater?
Let's say I have a repeater. Knowing all of the information about antenna height and gain in each direction, as well as power, how can I create a map similar to this map I saw of a repeater in Illinois?
Free options are always better!
Skyler 440
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21
votes
1 answer
Why do people say, "get a nickel," on repeaters?
Sometimes, I'll hear someone say "wait a moment, I'm getting a nickel," and then drop the carrier only to resume talking. Why?
webmarc
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21
votes
5 answers
Good wire for wire antenna?
What properties should I look for in a good wire for building a wire antenna? Could anyone recommend something specific for me?
Timtech
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20
votes
10 answers
What antenna on a BaoFeng UV-5R Pro will give me better reception?
I am happy with my BaoFeng UV-5R Pro but the local UHV VHF repeater and simplex reception is terrible, even for contacts less than 50 kilometers. I assume that it's because the rubber-ducky antenna on it is terrible. What can I replace it with that…
Warren VA7WPX
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20
votes
4 answers
What is the peak voltage at the tips of a dipole antenna?
What is the peak voltage present at the very end tips of half-wave dipole antenna in free space, and how might this peak voltage relate to transmitter type, transmitter power, RF frequency vs. antenna half-wave frequency mismatch, feed line, SWR,…
hotpaw2
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20
votes
2 answers
How to detect common-mode currents or “RF in the shack”?
Let's say we already know that if your antenna is not suitably constructed or connected then you can get current on the shield of your coaxial feed line which will flow through the shielding/grounding of your equipment, becoming “RF in the shack”,…
Kevin Reid AG6YO
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20
votes
6 answers
SDR: Quadrature demodulation vs direct RF sampling
I see that many SDRs use a quadrature demodulator and sample I and Q signals.
But is it possible to downconvert the RF signal instead, sample it with only one ADC, and get the same capabilities of digital postprocessing?
So if we want to observe…
BarsMonster - R2AYN
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19
votes
3 answers
What makes cellphone transmissions so energy cheap?
The modern cellphone can carry on a full duplex conversation for a time period measured in hours on a battery half the size of my handheld transceiver. My transceiver can barely receive for that length of time on its pack, nevermind transmit, and…
Adam Davis
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19
votes
1 answer
How does moving a feedpoint off-center in a dipole affect the resonant frequency and resistive load?
Specifically, I understand that OCF dipoles change the SWR, but does it do this via reactance or resistance, or both?
Bill - K5WL
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19
votes
5 answers
Why do folded dipoles have greater bandwidth than ordinary resonant dipoles?
This is something I've read in passing, but never encountered an explanation of why. For example, Wikipedia says:
Another common place one can see dipoles is as antennas for the FM band; these are folded dipoles. The tips of the antenna are folded…
Phil Frost - W8II
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19
votes
3 answers
How does a mag mount antenna achieve a ground plane?
I've been thinking for some time about magnet mount mobile antennas and wondering how they establish their ground plane. Consider that many mag mount antennas have some kind of protective coating on the magnet. Consider also that most cars have a…
Peter KB1AVL
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19
votes
3 answers
SDR sampling bandwidth - do the bits per sample matter?
I'm looking at data converter chips for a homebrew SDR design, and I see that I can choose not just the sampling frequency, but also the bits per sample.
Obviously the sampling frequency has to be several times the target frequency, but what effect…
Adam Davis
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19
votes
2 answers
Ham radio above 275 GHz
I see on the allocation chart all modes and frequencies are allowed above 275 gigahertz. Has anybody experimented with this? Are there interesting things you can do on these extremely high frequencies?
The bandwidth must be amazing here; maybe…
Skyler 440
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