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16
votes
1answer
7k views

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 ...
15
votes
4answers
84k views

Using my Baofeng UV-5R to talk to walkie talkies

I have a few walkie talkies at home and sometimes I connect my UV-5R to them to talk to them and act as another walkie talkie. At one time, I built a little simplex repeater out of it. Should I not be ...
15
votes
4answers
3k views

Are there federal laws (US) protecting antenna installation?

Are there any federal laws or FCC guidelines that allow ham radio operators to install antennas? I live in an apartment building in a large city that bans outdoor antennas. I recall reading that the ...
15
votes
3answers
8k views

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 ...
15
votes
3answers
2k views

Why does SSB have the hollow voice sound?

When I listen to SSB, it has the very familiar tunnel-voice sound. What properties make it sound like this? With a Carrier and an extra sideband as AM, I don't hear the tunnel-effect at all. Is there ...
15
votes
4answers
12k views

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 ...
15
votes
2answers
8k views

What does a noise blanker really do, and what are the side effects?

Most HF rigs have a noise blanker (NB) feature. It does reduce some types of noise (car ignition noise and such). How does it really work? I've read it has negative side-effects with strong signals, ...
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 ...
14
votes
4answers
2k views

OK to use any repeater?

There are a number of repeaters in my area, each belonging to a particular amateur radio club. These guys are all friendly and willing to chat but I was wondering if it was bad form to make use of a ...
14
votes
11answers
5k views

Is Morse code a digital, binary mode?

At first glance Morse code looks like a digital mode - there are dits and dahs, two values which contain the information of the transmission. Alternatively, at any point in time there either is a ...
14
votes
3answers
4k views

What does Ham mean?

Amateur radio operators are always referred to as Hams, it's basically the most common term for the hobby, at least around here. Where does the term come from? I heard that it's an acronym for ...
14
votes
4answers
6k views

If I receive an SOS signal, what is the proper response?

My 5-year old son loves sending out an SOS signal using a toy Morse code generator (wired, don't worry about false alarms for real authorities). He has learned to send the SOS signal and was asking ...
14
votes
2answers
4k 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 ...
14
votes
6answers
1k views

Where can one find recordings of Morse code, generated by humans and not machines?

I need some recordings of CW / Morse code for use in a project. Most of what I find is either nonsense (it just exists for the 'sound of CW', but doesn't contain a message) or is generated by a ...
14
votes
4answers
2k views

How can RF exposure hurt you?

In studying for the exam, one question came up about RF Exposure. G0A 07 What effect does transmitter duty cycle have when evaluating RF exposure? My ...
14
votes
3answers
579 views

Why do concurrent FM signals not mix together?

Generally when I hear two conflicting signals they do not mix together, but rather one dominates then the other. This phenomenon can be observed on FM broadcast station when driving out of range from ...
14
votes
4answers
2k views

Does a FCC amateur license cost money?

If I wanted a FCC Amateur license, is this going to cost me anything? That includes tests, application fees, filing fees, and anything else but hardware.
14
votes
2answers
15k views

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 ...
14
votes
3answers
2k views

What is a linear RF amplifier?

Most of the RF amplifiers advertised, and most of the questions about amplifiers, are "linear" amplifiers. What is a linear amplifier, and what other common amplifier type(s) exist that requires ...
14
votes
1answer
3k views

Is it a good idea to build your own radio transceiver today? [closed]

With all the advances in the field of electronics, microcontrollers, etc., is it a good option today to build my own amateur radio transceiver (or transmitter/receiver)? Why might one choose to build ...
14
votes
2answers
2k views

If I install a G5RV in my attic how could I be certain there are not harmful levels of RF in the shack, or my kids bedroom?

I assume that anyone who has a G5RV or G5RV junior in their attic has done so with ceramic spacers, and has zigzag or dog-leg installations, or otherwise has contorted the antenna to fit up there. My ...
14
votes
12answers
12k views

How can I safely transmit without an antenna tuner or SWR meter?

Just what the title says. An Antenna Tuner, henceforth AT, is almost a de facto piece of equipment in a shack; working the bands without one is tantamount to leaping off the diving board into a ...
14
votes
4answers
1k views

What should I consider when choosing a coaxial cable?

Given a middling-power rig (up to 100 W) requiring a 50 Ω antenna, a few options for the coaxial cable with a 50 Ω impedance are RG-174 RG-58A/U RG-8 RG-213 Apart from cost, what factors are ...
14
votes
2answers
924 views

Why is the solar-flux index measured at 10.7 cm?

Why is the solar-flux index measured at 10.7 cm? What makes that such a special frequency?
14
votes
1answer
6k views

How do I change my registered address with the FCC?

I just moved, and I want to change my registered address with my call-sign. Is there a form or something somewhere that I can fill out? Do I have to mail it, or can I turn it in to the FCC or ...
14
votes
4answers
4k views

What does the addition of a shield to a small loop accomplish?

A small shielded loop is an antenna with a loop of wire, smaller than 1/10th of a wavelength in diameter, also surrounded by a shield. Often, they are constructed from coax. There is a gap in the ...
14
votes
2answers
2k views

What defines music, per amateur radio regulations?

Sometimes when I access IRLP nodes, they have a very short melody telling you that you are connected; or when my local repeater's net begins, it does the famous doorbell 8-note sequence. What is the ...
14
votes
2answers
4k views

50 Ohm coaxial cable vs 450 Ohm or 600 Ohm ladder or window line?

What are the relative advantages and disadvantages of using 50 Ohm coaxial cable as opposed to 450 Ohm or 600 Ohm ladder or window line?
14
votes
4answers
505 views

Are amateur radio call signs unique among all radio call signs?

Idle curiosity: Are the call signs of amateur radio operators distinct from call signs in all other radio services, such that there can be no ambiguity even if the relevant license and band(s) of ...
13
votes
6answers
3k views

Why are vacuum tubes still used in amateur radios?

I wonder, even in this modern generation why the outdated vacuum tubes are used. In other electronic circuits they have been replaced by more efficient (and small) transistors years ago. Why they are ...
13
votes
3answers
1k views

WWV, WWVH, and WWVL may be shut down. Are there any alternatives?

The US government is proposing to shut down the NIST standard time and frequency stations WWV, WWVH, and WWVB in Colorado and Hawaii. If that actually happens, are there any free or inexpensive ...
13
votes
8answers
1k views

Why are Wullenweber CDAAs obsolete?

Wullenweber circularly-disposed antenna arrays (CDAAs) are large HF direction-finding antennas, sometimes colloquially referred to as "elephant cages", that were popular in the Cold War. They allowed ...
13
votes
4answers
1k views

When may a ham operate beyond the privileges of their licence class?

As far as I know, all radio amateurs are assigned privileges on Power Output Mode of operation Operating bands as a function of the class of licence they hold. These privileges differ from one ...
13
votes
3answers
33k views

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?
13
votes
5answers
5k views

How to operate IEEE 802.11 WiFi AP within the amateur radio service?

How can I properly use my ham radio license to operate an IEEE 802.11 WiFi access point within the US amateur radio service, rather than the US "part 15" regulations for unlicensed transmissions?
13
votes
3answers
242 views

Testing blind license applicants

My friend is blind and would like to take the amateur radio license exam. I understand that the question and the four possible answers can be read to them, and that is fine. The one question that we ...
13
votes
4answers
2k views

Handheld Dipoles

A problem with handheld devices is poor grounding. I read from someone else's question that dipoles don't need a ground. Why don't they make little handhelds with two antennas instead of one, or a ...
13
votes
4answers
805 views

Why do today's transceivers use LC filters rather than crystal filters?

Going through a number of schematics for today's receivers (Elecraft KX3, for example) I note that most use LC circuits for filtering. The wikipedia article for Crystal Filters suggests, however, ...
13
votes
4answers
3k views

How does a folded dipole work?

A folded dipole is like an ordinary dipole, but with the ends extended and folded back, until they meet. Although it looks like a loop, I'm told it behaves similarly to a dipole. How does this thing ...
13
votes
3answers
2k views

Is a vertical noisier than a dipole, and if so, why?

I've had people tell me, anecdotally, that a vertical is noisier than a dipole. Is this true, and if so, why? If it is true: Is this additional noise, such that SNR is degraded, or is the vertical ...
13
votes
1answer
4k views

What is the purpose of a balun and a unun in a feed line?

I have never understood how a balun or a unun works and under which situation I need to use either of them in an antenna feed line.
13
votes
2answers
6k views

When is RF grounding necessary, and when is it not?

I've seen many installations, particularly at field day and also in second-floor installations, where RF grounding is ignored entirely. What are the drawbacks to this and when is it absolutely ...
13
votes
4answers
2k views

Why does ice on a wire dipole affect the SWR?

We just had snow and ice overnight and my wire dipole was coated in ice. Why does the ice covering negatively affect the SWR of the antenna?
13
votes
2answers
1k views

How do I receive ATV with GNU Radio?

How do I receive Amateur television (ATV) — e.g., NTSC in the U.S. — with GNU Radio so I can play the A/V in, e.g., the VLC video player? Are there any example GNU Radio block diagrams to accomplish ...
12
votes
6answers
20k views

Calculating Antenna Length on the FCC Exam vs. in Reality

I have seen the following formulas for calculating half and quarter wavelength antennas: Formula for $\frac{1}{2}$-wavelength antenna (in free space): \begin{equation} \mathrm{Length~(feet)} = \frac{...
12
votes
2answers
2k views

How does selecting the opposite sideband when receiving CW on HF reduce interference?

I am studying for my FCC General Class license, and question/answer G4A02 reads as follows: Q: What is one advantage of selecting the opposite or "reverse" ...
12
votes
7answers
874 views

Can I transmit anything inside a Faraday cage?

Can I perform any transmission regardless of my license as long as I'm inside an RF sealed enclosure, such that no RF will be detectable from my transmissions off my property? I imagine the answer is ...
12
votes
3answers
2k views

How can I tell if a call sign is valid?

Many different countries have different callsign formats. The US call signs typically fit into a very well defined category, but there are exceptions even there. I'm looking for a way to tell if a ...
12
votes
3answers
5k views

How do I prevent radio signals from tripping a GFCI?

My wife woke up several nights by a metallic "thunk". It happened to be while I was talking on 10 meters and turned out to be the ground fault circuit interrupter (GFCI) on her hair dryer cord. ...
12
votes
3answers
436 views

What are the relative bandwidths of the amateur bands?

While I was operating on 40 m for Field Day, I noticed a higher SWR than when I first set my antenna tuner for the band. This happened, of course, because I was in a different part of the band, but I ...

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