17
votes
Accepted
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 ...
- 8,174
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-...
- 17.4k
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 ...
- 628
8
votes
Accepted
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 ...
- 6,960
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 ...
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, ...
- 17.4k
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 ...
6
votes
Accepted
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.
...
- 8,174
6
votes
Accepted
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 ...
- 52.5k
6
votes
Is there a proper way to connect multiple radios via coaxial cable so they can be tested without going over the air?
My company built a system like this, to allow real radios to be used in a flight simulator. It had fixed and digital variable attenuators, so it could simulate exactly the effect on communication of (...
- 12.2k
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 ...
- 347
5
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 ...
- 3,739
5
votes
Accepted
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 ...
4
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 ...
4
votes
Accepted
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 ...
4
votes
Accepted
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 ...
- 8,174
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 ...
- 52.5k
4
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 ...
- 52.5k
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 ...
- 52.5k
4
votes
Using a Return Loss Bridge and Nano VNA to measure amplifier characteristics
The quoted poster in the linked thread is suggesting to use an external reflection bridge but it is confusing why. The NanoVNA has a built-in directional coupler on Ch0 with maximum 0dbm output (and ...
- 41
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 – ...
- 7,469
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 ...
- 13.6k
4
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 ...
- 166
4
votes
Accepted
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 ...
- 4,658
4
votes
Is there a proper way to connect multiple radios via coaxial cable so they can be tested without going over the air?
A run of coaxial cable, with an attenuator, is a perfectly good way to simulate an “over the air” connection. It is done all the time in labs.
(However, note that it does not automatically mean your ...
- 25k
3
votes
Accepted
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 ...
- 9,320
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 ...
- 9,320
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, ...
- 4,669
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 ...
- 13.6k
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 ...
- 52.5k
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