Amateur Radio Stack Exchange
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1500 questions
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How is a 1:1 current balun different from a choke?

I have a 10m dipole and am going to feed it with 50 ohm unbalanced feed line (coax). My understanding is the feed point of this style antenna is about 50-75 ohms, and since it is a balanced antenna I'm thinking I need some type of balun. I'm…
Java42
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Is there an optimum transmission line length for maximum power transfer?

Consider a typical source -> transmission line -> load (i.e. TX->transmission line->antenna) arrangement and assume that the load is not matched to the transmission line characteristic impedance. It's always possible to select a length of…
Chu
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Connect two receiving antennas to the same radio

I have built a 1090 MHz ADS-B antenna roughly following some video instructions. It appears to work reasonably. However, because of how it is placed, it captures signals for more or less a half of the sky. So I would like to build another and put it…
Giovanni Mascellani
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Has a vehicle magnetic antenna mount ever caused a road accident?

Some people believe that mag mount magnets lose their effectiveness over time, eventually causing a dangerous situation as the antenna could rip loose from the vehicle and become a projectile or distraction at an unfortunate time -- e.g. on a…
Paul
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How does the baofeng radio eliminate squelch tail?

All tests are performed in Carrier Squelch mode on all radios without any sub-audible tone or digital squelch involved. Scenario 1: The Baofeng handheld radio Keys up. Another Baofeng is listening. When the transmitting Baofeng un-keys, the…
Skyler 440
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Building a portable event repeater

How does one go about building a portable repeater for use at events? Preferably at low cost, and with a minimum of bulky parts (so it's travel friendly). Obviously you'd need a pair of radios to handle RX and TX, taking into account that the TX…
Trevor Johns
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How to design a rubber ducky antenna

I am attempting to design an antenna for a 162.4 MHz omni receive only application and am confident it is going to be difficult if not impossible. I have very tight specs on space(6" diameter by 3" deep cylinder) so the first antenna I came across…
Josh Cox
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Why is the speed of light rounded to 286 Mm in calculations involving frequencies below 30MHz?

I understand that in order to make the maths simpler, frequency ($f$) is expressed in megahertz (MHz) and the velocity of propagation in free space ($c$) for frequencies above 30 MHz is expressed as and rounded to 300 megameters/second (Mm/s). The…
Dan
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Can I have multiple inverted-vee antenna fed by a single coax?

A friend who recently received his call is planning to setup an inverted-vee for 40/20m bands. Our take is the signal will take the path of least impedance into the correct length antenna wire. Something like the image attached; it depicts two wires…
VU2NHW
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Which qualities/features does an SDR radio device need to be usable for Amateur Radio?

I know what things to note when selecting an analog amateur radio, but SDR devices have completely different specs, e.g. sample rate and resolution. What do I need to know about the device to make sure it is suitable for working Amateur Radio…
jkj
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Phasing harness for antenna array

I understand that certain antenna designs (particularly phased arrays) require feeding each radiating element with a certain number of degrees of phase separation in order to achieve a desired radiation pattern or beamwidth. I found this 2-meter…
Craig
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Why is dynamic range relevant for an SDR?

Sometimes I see dynamic range mentioned as a figure of merit for an SDR. For example, I know that the bits per sample used by the analog to digital converter can affect the dynamic range. Why do I care about dynamic range? What happens when I don't…
Phil Frost - W8II
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Getting Started with Digital Modes on VHF on Linux

I am interested in learning about digital modes using 2m and Linux. I have a couple of older 2m rigs (HTX-212 and an old Yaesu) with no additional hardware, like a TNC. What current resources exist for hardware setup and software configuration for…
Rob Gibson
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Remote SDR on the internet other than WebSDR?

Besides WebSDR, what remote Software-Defined-Radio stations (for shortwave or amateur bands) might be available for open public access over the internet? What protocols do these SDR stations use to stream data over the internet? Do any of these…
hotpaw2
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Why are commercial SDRs so limited in operating frequency?

I spent a bit of time researching SDRs, mostly looking into the possibility of building an all-FPGA-based TRX. There are a lot of commercial ready solutions; some are cheap, some not, but they all tend to be operating from 50/70 MHz frequency…
Ulterior
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