34

Well, the canonical answer is that the balun converts the dipole (BAlanced) to coax (UNbalanced). But what does that mean? For transmission lines (twin-lead or coax) to not radiate, each conductor must carry equal and opposite currents. It's these equal and opposite currents canceling each other that results in zero net field away from the transmission line....


16

A dipole is a particular machine for creating EM fields. The idea is to set up a voltage between the two halves of the dipole in such a way that an EM field is created and efficiently radiated away. Remember, voltage is a difference between two things. When we consider just an dipole, with no feedline or anything else around it, it's very simple to see that ...


12

I'm going to approach this a little differently starting from roughly the same place. Here I am going to use a resonant $\lambda$/2 20m dipole driven by 100 W as the model. Let's compute the current at the feed point of a dipole at resonance, this is found with the input power (100 watts) and the feed point impedance; which for our dipole is assumed to be ...


11

Because of the skin effect, which causes most of the electric current to be concentrated around the outer surface of the wire at high frequencies, larger gauge wire is needed for RF than for an equivalent DC current. As a general rule of thumb, 16 gauge is sufficient up to 100 watts, but 12 would be ideal. Any system exceeding 100 watts really needs to have ...


10

Yes, a random wire can be a practical antenna. Anything conductive can be loaded up. Somethings work better than others. But if you want to play around, there's no reason the antenna has to be an "antenna". There are, of course, some drawbacks: You must have a tuner. You might not get a match on every band you'd like to work. For efficiency, you need a ...


9

Another answer mentions the paper by K9YC, Jim Brown. This is the best reference on baluns in amateur radio. See: http://audiosystemsgroup.com/RFI-Ham.pdf Chapter 6 is about baluns and antennas. He says, "The primary function of most baluns, at least in our ham stations, is to minimize the interaction of our antennas with the transmission lines that connect ...


9

The ARRL NTS (National Traffic System) is the method you would use to send messages to anyone anywhere in North America and in concert with other traffic systems to many parts of the world. NTS has many message passing scheduled times on multiple bands. In the night time hours, 80 meters is so popular that sometimes message trafficking networks are most of ...


9

When establishing emergency communications in a disaster, the natural choice of band is one that will allow you to communicate out of the disaster zone. Given the scenario you describe, a massive earthquake affecting the West Coast of North America from Northern California to British Columbia, that probably means HF. HF privileges with a US Technician ...


9

You have an SMA connector – use that! You can buy ready-made coax cables with SMA connectors on both ends. As mentioned, what you want is a coax cable. The electromagnetic wave travels within the cable, so, no, if not damaged and properly attached to the radio and to an actual antenna, it won't double as antenna. Very much like your TV cable doesn't emit ...


9

Why does this have an influence on the standing wave? Although there is no electrical connection between the folded sections at DC, that analysis neglects effects that are relevant at RF. Imagine a voltage step initiated at the feedpoint. It's important to consider not just the voltage at some point on the wire, but the fields around the wire. Let's assume ...


9

The cheapest antenna you can set up is a speaker wire dipole. A spool of speaker wire long enough to split the conductors and make a center fed half wave dipole ought to cost around ten dollars US (or less). You can get useful radiation with supports made from cheap stud lumber from the home improvement store (8-10 dollars per support to get 5 meters off ...


8

Here is an answer for the European hams among us. Printable copies are available from my web site. Wire myths There happens to be a lot of fuss out there about antenna wire. Most amateur radio shops sell "special" antenna wire at unreasonably high price, whilst most of the claims made about these wires are untrue. The situation reminds me a bit of the many ...


8

In short, no. In long, it's really complicated. The wider your wire, the wider the bandwidth, due to the increase in available paths. Wide multi-strand wire does better against skin effect (more conductive area). But, the "more exposed area" doesn't work here. You are picking up the E-field with this kind of antenna, so it's the voltages out on the tips ...


8

Assuming that both antennas are 50 Ω resistive, they will combine in parallel for a 25 Ω load impedance when transmitting. This will cause the transmitter to see a 2:1 SWR. This is a 0.333 voltage reflection coefficient so ~11% of the transmitter power will be returned to the transmitter from the tee junction. The remaining 89% of the power will be split ...


8

You should not make any coil in the middle of the antenna as that will greatly change its RF characteristics. Instead, bundle up the wire at the ends in some fashion: One practical solution is to fold the wire back on itself and fasten the free end onto the main line; then you have a loop you can also use for supporting the antenna, though you might want to ...


7

You can make the wire as thin as you want. There are two non-obvious things to point out: Firstly, as you make it thinner, resistive losses go up. You could make a worst-case calculation of the resistive losses by assuming the current is at a maximum everywhere in the antenna. If you put 20W into a 50Ω antenna, the current will be: $$ \begin{align} I^2 R &...


7

It's really hard to say, because it depends on so many things. Analyzing the antenna in free space simplifies some things, but we'd still have to consider the exact geometry of the antenna (How thick are the wires? Are they bent at all?) and the material from which they are made (any resistance will decrease the Q factor of the antenna, reducing the peak ...


7

If I connect two antennas to one radio using a t connector will it work? That depends on your t-connector. If your tee really is just a branch in the inner conductor and connected outer conducters, than the other two answers are correct: your input impedance will be different than your output impedance. If, however, the tee is meant to be used in a ...


7

Would the portable ~$40 Tecsun get damaged somehow by a 100-foot antenna because it's designed to work with shorter, portable antennas?  Unless you are within a kilometer or two of a very high power transmitter, there is no chance of your antenna collecting enough power damage your receiver. You are more likely to cause damage to your receiver from static ...


6

String trimmer line is engineered for high tensile strength, resisting breakage, but it isn't meant for 1) long term outdoor exposure and 2) long, stable lengths. Number 2 means it will stretch over time. Not a lot, but at the lengths needed to support antennas will needed to be tightened repeatedly over the first day or two, whenever the temperature warms ...


6

Send an HF-E-Mail addressed to your familymembers using a system like WinLink 2000 (http://www.winlink.org). It uses Radio Message Servers (RMS), which provide a bridge between the Central Message Servers (CMS) connected to the Internet and radio clients. Radio modes available for WinLink: HF Soundcard modes (requires audio cable between your HF SSB ...


6

First, I believe the 160/6 might refer to the antenna's coverage of the 160 meter band through the 6 meter band, with all other ham bands between included. Only important if you plan to transmit. If you're only interested in short wave listening, it simplifies the antenna requirement. My suggestion is to string up whatever length of wire you have. More ...


6

For receiving it should work up to a certain level. However, the impedance will be completely different from that of a single antenna. So the SWR will be too high for transmitting and reception will normally be less efficient than with a single antenna. The best way to use two different antennas is to use a coax switch.


6

It might be a good idea to start by trying to make a block diagram of what you have inside of each of those controllers... Namely, the drone controller is most likely some sort of a system on a chip, which on its own chip, in addition to having a microcontroller also has the radio interface built in. Those are two separate things, but in one package. ...


6

A wire will pick up a GHz signal, as well as a ton of other RF signals, all mixed together. Some sort of filtering is required to separate out your desired radio signals. An Arduino has none of filtering required. Sampling a 2.4 GHz signal requires a sample rate above 5 billion samples per second. The A/D on an Arduino samples at a rate of about 9000 ...


5

First of all, acid-core solder is never used for electronics any more, that just isn't what it's for. I think it's still used for plumbing or other soldering where there aren't sensitive components involved. Second, aluminum solder isn't a thing. The best I can find is that there's some solder specifically for soldering aluminum to other stuff, but you ...


5

Depending on the RF frequency and wire diameter, skin effect may dominate the effective resistance at that frequency. If so, since copper has a lower resistance, any resistive losses of a copper skin might be lower. Silver or gold plating would be even better, but a little too expensive except in exotic applications. However, pure copper also has a lower ...


5

The "rule of thumb" for keeping the skin effect at bay is to use conductors that have a diameter greater the twice 3-5 skin depths. Twice the depth because if you can envision the wire having RF current develop a tapered current density from the surface inwards to the center, you go half way in and half way out, 2x. So for 1-skin depth in copper of 1.37 mils ...


5

Be sure that the wire that you use is acceptable legally as well as physically. In any place were the National Electric Code (NEC), that is used in much of the United States, is enforced as law the minimum size of wire that can be used for an amateur radio transmitting antenna is number fourteen American Wire Gauge (14AWG). For people in other parts of the ...


5

First problem is how to connect the transmitter antenna to the signal generator. I will use a 50 ohm coax cable of small length. Since the waveform and directivity is not critical, could I get away without adding a balun? Or would there be a risk of damaging the signal generator with signal reflections (it has 50 ohms and +10 dBm (0.01 Watts) output) ? A ...


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