Hot answers tagged

22

There's always a ground. Whether it's what you intend it to be or not is another issue... A mag-mount antenna is grounded through capacitive coupling between that magnet and the metal it's stuck to. At VHF/UHF frequencies, this effect is adequate for good results which explains the popularity of these mounts. Some folks advocate adding a wire instead of ...


15

While for an authoritative answer to this I believe you'd have to ask the manufacturers directly (unless we happen to have someone here on the site who works for one of them), there is a pretty big plausible reason why so few multiband radios include 220 MHz capability. The band is allocated to amateur radio mostly in the United States and Canada. (Source: ...


13

220MHz has a long and storied history which leads to the lack of available equipment, and thus low adoption rates in the Amateur Radio community. The short version is that two things contributed to its lack of usage: Few commercial bands are near enough that existing equipment can be simply modified to serve this band. There are numerous commercial bands ...


11

In the absence of common-mode currents, then the optimum feedline length is 0, because a longer feedline only increases your feedline losses. These losses are due to the resistance of the wire, dielectric losses, etc. and are specified in dB per unit length in the coax datasheet. At VHF and up, these losses can be significant even at car lengths, especially ...


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 ...


8

Magnet mounts can come off, and they do fall occasionally. I can't quote any statistics, but it has happened to me twice in the past - tall HF antenna combined with too small magnet mount and high speed. Luckily the cable held the thing on the roof. Short VHF/UHF sticks (think 1/4 wave for 2 meters) would never fall with the same mount - the wind load is ...


8

The antenna itself won't be significantly affected by the water. However, waterproofing the coax connection is essential. If this is not done, water will creep inside the coax by capillary action and ruin the coax. There are several products that can be used, for some examples see 3M's application guide. However all have three elements: An underlying ...


7

Insofar as there is an agreed-upon definition of the term “mobile” (and “portable”, which is closely related/confusable and so I'm covering it here), this is how I have most frequently seen the terms used when people are being precise about it: Portable: A station set up in a temporary location. If you've parked a radio on a picnic table and strung a wire ...


7

There are two reasons for the advice to run direct to the battery: Minimize the area enclosed by the power connections. This reduces both interference picked up by the wiring, and inductance (which is undesirable in power supply connections). Minimize resistance. A radio can be a fairly heavy load as car accessories go, so you want to avoid any voltage drop ...


7

Part 90 certification is required for radios used in the USA in the land mobile services - often called commercial radio. No such certification is required for the amateur radio service. The closest we come to certification is Part 15 for our receivers and Part 97 for our linear amplifiers - but only if in either case they are commercially produced and sold ...


6

Batteries can be approximated as an ideal voltage source in series with a resistor. So it's perfectly normal for a battery's terminal voltage to drop when the current it is delivering increases. To determine whether that's actually a problem, you only need to consider two things: Is the new voltage too low to power your transceiver? Are you exceeding the ...


6

It's hard to make guesses about this sort of thing because there are too many different factors. The mag mount antenna certainly is better than your FT60 antenna, and the 75 watts is certainly better than the 5 watts - but how much is subject to a number of factors. To get a good guess you can use that doubling the range requires four times the power (which ...


6

If you search for "automatic power off car ham" you'll find a number of solutions which don't require additional wiring. When the engine is running the voltage supply is higher than when the engine is off, so these work by sensing when the voltage is high enough, and turning the radio on.


6

While many transceivers and scanners can be powered by a cigarette lighter adapter, you typically want to run at most one transceiver in this way, and should make absolutely certain that you know where that lighter is getting powered from. Most car fuseboxes are relatively easy to access, and most owners manuals will tell you what fuse is associated with ...


6

A horizontal VHF dipole above a (presumably metallic) car roof is not a good idea. Because the car roof is relatively large relative to wavelength, and is a good conductor, you will get a lot of RF current in it through capacitive and inductive coupling. This isn't a bad thing in itself, but because the geometry of your car isn't designed as an antenna, the ...


6

According to ARRL: Identification for US amateurs is the US call separated by a stroke and the appropriate Canadian prefix identifier (e.g. N1KB/VE3) In every case I can think of, one is required to identify the location from which they are transmitting, if it is not in their call sign, or at least a different country. And usually they want more than ...


6

I own some of Buddipole products. Buddipole is really a system rather than a product per say. It's based around being able to create an effective antenna that is both portable and has flexibility for configuration. The real heart of the system is the VersaTee and the fact that all the parts for all the products use the same size threaded connector. All ...


6

The only thing you need to do is make sure you can receive mail at the mailing address on your license, because that is part of the obligation of holding a license. It doesn't have to be your ‘residence’ or your true address in any sense; you can put down the address of a friend who'll read it for you and notify you of anything important, and that'll satisfy ...


6

The relevant regulation is §97.23: Each license grant must show the grantee's correct name and mailing address. The mailing address must be in an area where the amateur service is regulated by the FCC and where the grantee can receive mail delivery by the United States Postal Service. Revocation of the station license or suspension of the operator license ...


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

This image of the bottom side of the bracket was taken with a flatbed scanner. The depicted dimensions were taken separately using a caliper, not by measuring on the image. The white inner area is the paper over an as-yet-unused adhesive pad; the material of the bracket is black-painted metal. Unprocessed image


6

Water has a drastically different relative permittivity $\varepsilon$ than air (water: ca 88, air: pretty much 1); it is, however, pretty non-conductive, just like air (being distilled and all). In a good approximation, uniform mixtures of substances with grain sizes significantly below wave length can be represented by a metamaterial with electrical ...


6

A low SWR bandwidth is a consequence of shortening the antenna for mobile use. SWR bandwidth is related to the antenna system's Q factor, the ratio of energy stored to energy dissipated per cycle. A higher Q means less SWR bandwidth. Decreasing Q will increase SWR bandwidth. That can be done by decreasing the energy stored, or increasing the energy ...


5

Voltage drop is caused by internal resistance Using batteries you will always experience a voltage drop when drawing significant currents, due to the internal resistance of the battery. This can be thought of as a resistor that is always in series with the battery, and consumes energy depending on the current drawn from the battery. It’s the main reason ...


5

Some radios, such as the Yaesu FT-857D, have a feature in the menu that allows you to set the unit to automatically power off after a user-chosen period of time. Search the documentation of your radio for such an option.


5

Any reputable mag mount antenna will be a huge gain compared to the rubber ducky. I routinely can hit mid-level repeaters from about 15 miles away with my mag mount setup and 5W. If I'm extremely careful, I can hit the same repeaters from 5 miles away with the rubber ducky antenna, in order to pull that off, I have to hold the HT perfectly straight. One ...


5

If your car uses petrol (gasoline) rather than diesel, then the ignition system can potentially generate a lot of noise because of the high-voltage system used to generate the sparks that ignite the fuel. Electric motors such as those used in the windscreen washer pump and/or wipers (or electric windows, etc.), can also generate noise. This would mean that ...


5

The effect of motion is to cause Doppler shift in the received signal. This changes both the carrier frequency and the symbol rate. However, because the speed of propagation of the wave — an electromagnetic wave — is the speed of light, this effect is very small for terrestrial conditions. A link between a fixed station and a vehicle moving at, let's say, ...


5

All kinds of digital microwave technologies can do this, including WiFi. It takes a good antenna location high from the ground, and good antenna gain / transmit power. Commercial wireless ISPs do it regularly. With a good antenna and cooperative terrain (no hills in the way), it could be done with consumer 802.11 equipment. Mind the link budget, and the ...


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