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17 votes
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How did hams manage to tune their antennas before VSWR meters?

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 ...
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13 votes

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

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-...
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13 votes

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

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 ...
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  • 519
7 votes

Cause of harmonic spurs?

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, ...
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7 votes

What does an antenna analyzer tell me about these coaxial cables?

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 ...
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6 votes

How to detect common-mode currents or “RF in the shack”?

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 ...
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6 votes
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Is this "floating" output single-ended or differential and against GND or VCC?

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 ...
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6 votes

VNA basics, antenna coax cable

If you want to understand what your radio "sees", which is probably the case, then you want to measure the entire system including the cabling to the antenna rather than just the antenna ...
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  • 186
6 votes
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VNA basics, antenna coax cable

You want to use the VNA against the final system configuration... or at least as much as practical. Why? The antenna's environment and transmission line will impact its characteristics. It's pretty ...
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  • 2,843
5 votes

Supershield or Superscreen coax: Does it exist? What is its common name?

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 ...
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5 votes
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What safety procedures should be followed when developing and testing a high power amp?

Get yourself a dummy load. If your gut is telling you your doing something stupid you're doing something stupid. Keep the power supply switch near by. Always assume it's live. If you have doubts about ...
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4 votes
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Testing for 'Bad' Coax

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

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 ...
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4 votes
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Can I have a signal generator on while it's not connected?

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 ...
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  • 7,485
4 votes

What does an antenna analyzer tell me about these coaxial cables?

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 ...
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4 votes

Can an oscilloscope be used as an RF voltmeter?

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 ...
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  • 3,323
4 votes

Why is my experiment to produce 3rd order harmonics by saturating a receiver not working

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 ...
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4 votes

What is a "feed-through load" and how does it work?

I think the correct way to understand this is basically as "a dummy load which makes it easy to measure the voltage across itself". Likely as simple as: simulate this circuit – ...
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4 votes
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How do businesses develop and test amateur radio products in the US if you cannot be paid for amateur radio use?

Two parts to this answer: First, most testing would be done against dummy loads, looking at the results on spectrum analyzers. Such tests should not propagate. Secondly, there's a fine line here. As ...
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  • 4,178
4 votes

What safety procedures should be followed when developing and testing a high power amp?

If you do have to stick a scope probe or adjustment tool into it, take off all your rings, watches, bracelets, necklaces, etc., before reaching into anything (or around any uncovered circuitry) that ...
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  • 12.4k
3 votes
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How can I determine the possible damages of transmission with detached antenna in portable ham radios?

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 ...
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  • 8,922
3 votes

How can I get a license to build broadcast transmitters?

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 ...
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  • 8,922
3 votes

How can I get a license to build broadcast transmitters?

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, ...
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  • 4,281
3 votes

Testing for 'Bad' Coax

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 ...
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3 votes

How did hams manage to tune their antennas before VSWR meters?

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 ...
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3 votes
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Testing Radios Back-to-Back without Going Over-the-Air

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 ...
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3 votes

Building a low-power simple RF frequency (433MHz or 900MHz (but not both)) detector effective at 5m with a 10mW signal

Well, your GPIO will need a defined voltage level and a couple of µA of drive strength, so completely "passive" is probably not really possible. Now, you'll need the following: Antenna ...
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3 votes

Building a low-power simple RF frequency (433MHz or 900MHz (but not both)) detector effective at 5m with a 10mW signal

I'm going to disagree with Marcus and say that you can probably get this to work, for some relaxed definition of "work". The detector you've drawn has poor selectivity, meaning it will ...
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3 votes

Can an oscilloscope be used as an RF voltmeter?

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 ...
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  • 12.4k
3 votes

universal 433 MHz test lamp (receiver)

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 ...
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