Hot answers tagged

31

"Getting a nickel" is a reference to how metered pay phones work (worked?). You'd put in some coins, make your call, and when the time you'd payed for expired, the phone operator would demand another nickel to buy more time and keep the call going. Repeaters on automatic control typically have a "time-out" function that acts as a ...


19

Every time I purchase a cheap HT such as the Baofeng you mention I also spend another $10 or so on an antenna, as the stock antenna is noticeably worse than even an inexpensive antenna like the Nagoya NA-771. There are still better antennas than this, but there are always tradeoffs. The stock antenna is one third to half the length of the NA-771, which is ...


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: ...


15

A homemade "rat-tail" ground plane costs 35 cents each to make. A crimp on eyelet to fit your antenna's connector, a string of speaker wire about 19-20 inches long and a little heat shrink tubing to dress it up and done. Soldering the the wire to the connector instead of crimping it will be a better option. Go here for some details about the "Rat-Tail" ...


15

I have a scanner capable of HF receive, multiple HF receivers, and several HF SDR transceivers capable of receiving on more than one amateur band slice simultaneously. Lots of contest stations run more than one receiver at a time to "pounce" on whoever pops up on any of several bands. When using a radio with a scanner, or a station with multiple ...


14

There have been a number of good answers already, though I think there are a few additional points worth sharing. Answers would also be more relevant if we knew what situation(s) you were coming up short range wise. For portable use (out in the field): The stock Baofeng rubber duck antenna has been shown to be a poor performer. All of the stock rubber ...


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 ...


13

They don't always do that, but the reason for it is simply separating the transmitted RF from the received RF. A ground-based repeater uses a fairly large duplexer to make sure that its transmissions don't feed back into its receiver; with a satellite, size and weight are at a premium, and having two widely separated frequencies requires much less hardware ...


13

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 ...


13

Short answer: Math says max link rate is 2Mb/s if you knew the perfect channel coding. Which is still an unsolved puzzle. Long answer: You're calculating a link rate. That is fine, and can be answered using Shannon's Channel Capacity, which gives us the upper limit for bits per second that we can get across a given channel: $$ C= b\cdot \log_2\left(1+ \...


11

Most modern VHF/UHF FM mobile rigs designed for Amateur Radio use have a "data" connector on the back. Currently manufactured dual-band examples include Yaesu FT-7900, Kenwood TM-V71, Icom IC-208H - they all have the same 6-pin mini-DIN "data" connector using the same main pinout. The 6-pin data connector is originally designed for attaching packet radio ...


11

Requirements: Less than $100 Commercially available Better reception than stock antenna Excellent portability Recommendations: Nagoya NA-771 Nagoya NA-701 Tram 1185 (Vehicle) Nagoya NA-771 Cost: $11 on Amazon.com as of March 2014 Length: 396mm Weight: 37g Nagoya NA-701 Cost: $10 on Amazon.com as of March 2014 Length: 211mm Weight: 40g Tram 1185 Cost:...


11

Electromagnetic hypersensitivity does not exist. There is no confusion. It has been rigorously refuted by science. One watt is orders of magnitude below safe exposure limits, and indeed probably less than exposure you are likely to get from cell phones, commercial broadcast stations, WiFi, and unintentional radiation from all kinds of electronics.


11

It may have served a purpose in the past, with less filtering in transmitters and receivers, no digital frequency displays &c, e.g. to avoid mistaking a harmonic on a higher band for the transmitted signal.


10

One would usually call CQ DX, but on 2 m FM that would sound a bit odd. Also FM will be heard by many people close by, who will find CQ DX quite funny. You could simply call and explain what you're trying to achieve, some hams would find that interesting and reply. If you find anyone on a calling channel, you could talk about the weather for a bit and then ...


9

This is an ill-posed question, since "best" could mean so many things. If VHF is so plainly best, why does anyone bother with UHF at all? If you mean what option has a lower path loss, then sure VHF is the better option. But then HF would be even better. And why not go with ELF? As the frequency decreases, so do free space path losses. Well, an ELF antenna ...


9

Apart from historical reasons it's also a filler. When calling CQ on SSB you probably want to stretch out your transmission a bit because that's what you need to get heard. In theory you could just say your Callsign and "CQ", as it is enough information. If people would hear each call immediately it would suffice. In practise expanding the length ...


8

Sure, most radios have the ability to patch in audio. If it isn't through the front microphone connector, it's through an accessory connector, which is available on every commercial radio I'm aware of - although perhaps only on a few amateur mobiles. But why would you want to? SSTV and PSK31 cannot be reasonably transmitted over FM. FM transmits a carrier ...


8

The ionosphere typically neither reflects nor absorbs waves with VHF or higher frequencies, but passes them through to space. There are no reflections back to the ground, so there is no useful propagation between stations on the ground. Tropospheric ducting is a different propagation mode which does carry VHF signals well, and is actually sought and used ...


8

My trick is instead of cutting, rather extend the whip first, and see if the SWR gets better or worse. Extend it 1/2" with a bit of wire wrapped around it and sticking out. If the SWR gets better, then you made it too short in the first place. If it gets worse, you can start trimming. Remember you should only measure SWR when you are away from the antenna - ...


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

I will need a UHF/VHF diplexer on either end to suitably merge/split the signals from each antenna Yes, this is correct. A tangent: If you wanted to save some money by using mass-market parts, you could use 75 Ω power dividers (coax splitters) instead of diplexers. This has 3 dB loss because the signals are not directed exclusively to the intended ...


8

… Why don’t these unencrypted FM emergency services seem to use any call signs … ? They aren't required to and don't find it useful in their procedures. Also, they don't have call signs in the sense amateurs do — they may have names for different groups in a transmission ("Car #3" or whatever) which are call signs in the sense that they play the same role ...


7

Summary: Theoretical maximum in the neighborhood of 10s of megabits per second. Less than that in practice, perhaps a lot less depending on budget. Let's start with the Friis transmission equation: $$ P_{r(\mathrm{dB})} = P_{t(\mathrm{dB})} + G_{t(\mathrm{dB})} + G_{r(\mathrm{dB})} + 147.6 - 20 \log_{10} (rf) $$ Insert the values you've given for ...


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

"Tone", displayed as "T" on the main screen, selects tone encoder + carrier squelch (your HT will send a tone, selected by the TONE Freq menu, and receive any strong-enough signal, regardless of whether it has a tone.) The transmitted tone is necessary to "open up" most repeaters so that you can talk on them. "CTCSS", displayed as "CT" on the main screen, ...


6

If you don't need mobility, purchase an inexpensive directional 4 element Yagi antenna for 2m and operate it in vertical polarization, that is with the prongs of the yagi pointing up and down. You can sometimes find these small Yagi antennas used for ~$20-30. But note this will only help you for 2m, and should not be used on 70cm. For 70cm you can get a ...


6

2m isn't a good band if you want to do anything digital. Digital modes just aren't very popular on 2m. I think the only digital activity you are likely to find is: D-STAR APRS D-STAR uses GMSK, but the data for voice transmitted on that channel relies on a proprietary codec called AMBE. Any software that can encode or decode it is almost surely illegal, ...


6

I am not a lawyer, and this is not legal advice. I'm also not particularly familiar with MURS, and generalizing from other information. According to Wikipedia, MURS (as many other US unlicensed radio services do) requires the use of type accepted equipment. (Terminology note: radio services are CB, FRS, GMRS, MURS, amateur, commercial, etc.) This means ...


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