Hot answers tagged

17

Mostly, they used RF Ammeters in series with the antenna. The first ones were hot-wire ammeters which were completely mechanical devices. One end of a thin nichrome wire (or other wire of sufficiently high resistance) inside the meter was coupled directly to the pointer shaft (often wrapped around it); the other end was anchored to the meter case. As the ...


14

One way to tell is by its effects. Do you hear a garbled version of yourself in nearby speakers when you transmit SSB? Do GFCI outlets pop even though no one is being electrocuted? Does handling the transmission line give you RF burns when transmitting, or change what you hear when receiving? If you had these problems and now you don't, you must have been ...


12

I'm still a beginner in this area, so take this answer with a gran of salt. I've had a chance to see a ham test repeaters few days ago, so I'll describe what he did: First and the most obvious, make sure that the transmit and receive frequencies are correctly set on the radio. Go to frequency of interest and listen for a while. If there is a conversation ...


12

GPS-based frequency standards @larsks answer rightly pointed at devices that use GPS to generate the 1-second pulsing. That's the correct way to go. Curiously, these modules only address the once-per-second accuracy issue, not the frequency standard issue, which GPS is indeed commonly used to solve: You'll find a lot of modules on the market that will ...


12

In No WWVB? No problem!, KB6NU points at two projects that show you how to build your own low-powered WWVB-replacement to keep your clocks in sync: μWWVB: A Tiny WWVB Station. This project uses an attiny44 microcontroller and a USGlobalSat EM-506 GPS module to simulate WWVB. One Component Radio Clock Time Transmitter: This project uses an attiny45 ...


7

You've nailed this! So, I'm sometimes involved in these kinds of investigations. It all gets easier when you have control over the transmitter – when some spurs disappear as soon as you turn it off, but others remain, you've ruled out the transmitter as the source of these. Then, digital receivers typically, as you notice, have different sources of spurs. As ...


7

WWV and WWVH broadcast time and frequency reference information continuously, using AM on 2.5, 5, 10, 15 and 20 MHz, so you should be able to pick up all of them using your receiver, given an adequate antenna. At my location (San Francisco Bay Area) with lousy equipment, these signals are only slightly stronger than shortwave broadcast stations, but more ...


7

My name is Alex, I'm the head of technical support at RigExpert. This is actually an interesting question. Our engineers could not give an exact answer why the schedule in the second case behaves strangely. I can offer to perform another experiment - to measure the parameters of the RG-8/U coax cable using the analyzer and the AntScope and AntScope2 software....


6

The other part of me thinks that the DC blocking capacitor will be a low impedance at RF so that the RF is actually "pushing against" GND or VCC but I don't know which one. This appears to be a kink in your understanding. RF doesn't "push against" one or the other. Let's be more specific about what we mean by "pushing against": ...


5

Another way to detect current on the outside of coax is to run your hand up and down the coax wile an analyzer is connected , if you see a fluctuation on the meter then current is following on the outside. On vhf I built sleeve chokes to remove it with great results. KC5ULU


5

It turns out that these cables were made by TE Connectivity. Some time back, they sold that business to Commscope. After talking to Commscope, it looks like those cables no longer are made. :( Their recommendation is to use FSJ1-50, even though RG-214 has a lower transfer impedance at this frequency, because the shield coverage is better. So I will have to ...


4

Part 15 sets limits on unlicensed RF emissions. The limits vary by frequency, the type of device, the nature of the emissions, and so on. It's a pretty huge document and you need a lawyer and an EMC engineer to approach it. However, you can get the intent of it from this blurb that is printed on just about every piece of consumer electronics sold in the US: ...


4

You're on the right track with the first items in your list. Assuming that you have a wattmeter and a dummy load that both match the impedance of the coax, it's a simple matter to measure the loss. Measure the power with the wattmeter at the source, and then measure it again at the load. The difference between the two wattmeter readings is your loss. $$N_{...


4

It's not necessary to turn it off while it is not connected. Zero dBm is a power level of only 1 milliwatt, and no device will be damaged by that power level. If it were, the manual would have said so.


4

I get that reflections show up as peaks on the IR graph, is that it? Yes, that's essentially it. Note that the reflections can be negative or positive: for example if you try it with a short at the end rather than an open you should get a negative spike in the impulse response. Falstad makes (I think) a pretty intuitive way to demonstrate the concept: ...


4

One of the functions of an oscilloscope is actually to measure RF volts, just make sure to use the x 10 function to minimize loading on the circuit you are measuring, and keep in mind that some high impedance circuits will still be affected even if you use the x 10 function.


4

Receivers have passive band-pass filters at their input. Except possibly ferrite cores (which are unlikely to be used for a filter above HF), the components used to construct these filters are very linear. For a receiver tuned to 471MHz, the output of your signal generators at 157MHz is surely well within the filter stop-band. Although the filter's stop-band ...


3

If you use a dummy load on the transmitter, it is likely that there will be enough power and enough leakage from either the load or the transmitter itself to be easily received. This is quite likely for the power levels and shielding quality in amateur equipment (homebrew or commercial). If you had a non-leaky or very low-power transmitter (e.g. the various ...


3

I have been a ham for 58 years. I used an incandescent light bulb for transmit and a fluorescent tube for antenna tuning. Later, I could afford a field strength meter. I have also used Lecher wires for UHF. Technical details? Go with the glow.


3

Don't forget about CHU (and here is the official site) which is the Canadian equivalent to WWV. It's at lower power and it's not as well-located geographically (it's located near Ottawa), but it's receivable in most of the eastern US and increasingly less well as you head west. Here in VE5-land (Saskatchewan) I certainly receive it sometimes, but I also ...


3

Either of those choices are good, as long as you identify your transmission. Many repeaters transmit a courtesy tone after repeating their input in order to signal end of transmission. For those repeaters, you can TX your call sign and then listen for the courtesy tone on the repeater output. This will let you know if you're hitting the repeater, but not ...


3

Depending on what you're testing, The safest bet is through a SWR meter into a 50 OHM dummy load, or an attenuator into a spectrum analyzer.


3

Depends on your receiver sensitivity and antenna location. I've seen some many-decades-old portable shortwave radios pick up at least one WWV frequency using their simple built-in half-meter to meter long metal whip antenna.


3

A cursory physical inspection and an SWR sweep are usually sufficient. Blatant physical damage, like internal shorts or breaks in continuity, will be found by the SWR sweep. So in your physical inspection you're looking for things which might not impact the SWR, like outer insulation that's cut or damaged which may eventually lead to water ingress. You ...


3

As implied in other comments and answers, this sounds like it would be legal to do (we’re all assuming you’re in the USA, given the fcc tag), since all you are doing is building equipment. However, if you want to sell the equipment once you have built it, that is going to be more difficult. I would ask you the question - why broadcast equipment ...


3

No license is required to build broadcast transmitters in the United States. To get approval to sell your transmitters in the US, you would most likely need FCC authorization. The process to get that authorization is covered by 47 CFR part 2, and is summarized on this FCC web page. I'll summarize further: Determine FCC Rules that Apply. Determine if ...


3

If your nephew damaged the Baofeng GT-3TP Mark III, the damage is likely to the transmitting circuits of the radio, and not to the receive side. I don't have that model of Baofeng, but I do have a different model, which is notorious for having difficult-to-adjust squelch. On several channels I can't get the squelch to stop the radio from playing static. ...


3

Maybe. If measuring a circuit output that expects a load impedance, such as a 50 Ohm coax or antenna, then to measure the RF voltage at that point with an oscilloscope, you should terminate that circuit output with the expected impedance (a dummy load), and measure the voltage waveform across that impedance load with a much higher impedance probe (x10 or ...


3

It is not generally feasible to detect "anything". The problem is there's always something, even if it is just noise. To know if something is signal or just noise you need to know something about the signal, but when you want to detect "anything" this means you must enumerate every kind of signal that could exist, which is of course not ...


2

Another great way to listen for signals, especially stronger ones, other than WWV and WWVH, is to find some active AM broadcast stations within the 1.8 to 30MHz range. Head over to this site http://www.short-wave.info/, and use the top most form, selecting any station, and preferred language, make sure NOW is checked, and hit GO! YOu can pretty much tune ...


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