23
votes
Accepted
How does an SWR meter really work?
Dispelling the Myth
To begin with, the typical HF SWR meter does not have the ability to separately sample the forward and reverse power, voltage, or current. Any description of the device or its ...
- 18.4k
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 ...
- 7,686
9
votes
Accepted
Do I need a separate SWR meter if the transceiver has one built-in?
You'll be fine to start without an additional SWR meter.
An SWR meter doesn't provide any protection. With or without an SWR meter, you'd want to start on a new antenna on low power, then increase ...
- 51.1k
8
votes
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Do you need to analyse the SWR of your radio repeatedly? Or periodically? If so, Why?
If nothing about the physical situation changes, then the SWR will not change. But something might change in the long run, perhaps:
Damage to the feed line (water intrusion, sun damage to insulation, ...
- 23.9k
7
votes
RF Bridge Problem - K6BEZ Antenna Analyzer
(See updated information further down)
I found an article to address the problems all in one place in QST, September 2019. The author addresses the same problems in the question, and explains his ...
- 385
6
votes
Accepted
Can I touch the ground of a PWR/SWR meter?
There's no problem with what you're proposing, usually.
Most of your other equipment probably has exposed metal connected to “ground”. If it's not causing trouble, this won't either.
But if you have ...
- 23.9k
5
votes
Accepted
SWR Measured at the Transmitter versus SWR at the Antenna
Given the matched loss of the feedline and the SWR at the transmitter, we can calculate the SWR at the antenna in three simple steps.
First convert the SWR at the transmitter to the corresponding ...
- 18.4k
5
votes
Accepted
What's the difference between a Return Loss Bridge and a Circulator?
For an ideal circulator, all the power entering one port exits the next port in the rotation and no other. So all the power in port 1 exits port 2, all into port 2 exits port 3, and all into port 3 ...
- 51.1k
5
votes
Accepted
Can a CB SWR meter be used for HF amateur bands?
Many hams have re-purposed CB SWR meters but there are so many variations that some caution and testing is warranted.
Many CB meters were not designed to handle the higher power levels of amateur ...
- 18.4k
5
votes
Accepted
Powering transceiver and SWR/power meter from same supply?
This should not be a problem at all. It is commonly done this way. Hopefully the switching supply has been designed for ham radio use. If not, you may find some "birdies" on your receiver which are ...
- 18.4k
5
votes
Accepted
Does the impedance along a transmission line change when there are standing waves?
VSWR is related to the magnitude of the reflection coefficient $\Gamma$:
$$ \text{VSWR} = {1+|\Gamma| \over 1-|\Gamma|} $$
The reflection coefficient can be calculated from the load impedance $Z_L$ ...
- 51.1k
5
votes
Why is my diplexer such a spectacular failure?
You have soldered a 68nH inductor instead of 100nH!
Maybe the layout and the wiring also play a key role.
Here's a vintage commercial one.
It's quite compact. The size, inclusive of the coaxial ...
- 737
5
votes
Why is my diplexer such a spectacular failure?
Like you, I modeled your diplexer in LTSpice, but I don't find the results to be acceptable. At 147-MHz, the input impedance is 87$\Omega$; at 443-MHz, it's 24$\Omega$. Also, the crossover frequency ...
- 7,798
4
votes
Accepted
Am I calibrating my SWR meter, SWR-001, correctly?
The calibration procedure is only used for determining the SWR - the forward and reflected power reading are not impacted. If you change power levels or frequency, you need to perform the calibration ...
- 18.4k
4
votes
Lightbulb as an SWR detector?
Mainstream hams first started to appreciate SWR in the 1940's. In that era some of the first SWR meters started to come on the market. But their accuracy and frequency range was quite limited. Toward ...
- 18.4k
4
votes
Lightbulb as an SWR detector?
I don't know much about this, but for what it's worth I do have a rather distant memory of doing this long ago, before transistor RF power amps became affordable and before I had a way to measure SWR ...
- 311
4
votes
Accepted
Why some hams test their baluns with an SWR meter?
A balun has two functions:
present a high impedance to common-mode currents
present a low impedance to differential-mode currents
A balun that does just the first but not the second is easy: an open ...
- 51.1k
4
votes
Accepted
Do External Signals Affect Antenna S11/SWR Measurement?
Yes, in my experience antenna measurements on a VNA are affected by external transmissions. They look like "noise" on the graph.
Usually you can exclude them by eye - they're narrow and sharp while ...
- 9,804
4
votes
Accepted
ZS6BKW deaf on all bands except 40
I have a homemade ZS6BKW antenna so I might be able to provide some insight, even though I've only used it for a few weeks now. I get good reception on 40m and 20m with it (when conditions are ...
- 156
4
votes
Do VNA (nano) suffer the same effect of coax length to swr, as swr meters do?
The NanoVNA, and any VNA, when calibrated with open, short and load standards, can correctly measure through an arbitrary two port network, like a lossy, imperfect cable.
Any combination of ...
- 9,804
3
votes
Why some hams test their baluns with an SWR meter?
A 1:1 choke-balun has a design impedance, usually 50 ohms. It also has an electrical length, e.g. mine is 60 degrees long on 28 MHz (4 feet of RG58 on two FT240-52 cores). If I load it with a 50 ohm ...
- 1,646
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 ...
3
votes
Accepted
To which part of the band should I tune my Hi-Q wire antenna if my transceiver has an automatic antenna tuner?
You should trim it so that the SWR is the same at each edge of your band segment of interest.
If you tune it for the lowest SWR in the middle, you likely will find that the the above condition does ...
- 7,686
3
votes
Why SWR significantly changes with adding 10-30 meters of coax in presence of RFI choke?
The repeating hi-Z measurements seen when SWR is measured with the 30m line suggest that it is defective. One needs to know the velocity factor and loss of the cable to determine the location of the ...
- 7,798
3
votes
Accepted
Looking for criticisms on my VNA-like SWR meter I am designing
I think the problem you will run into is that people will want this to be plug and play. They may not have a directional coupler, or know or feel like to calibrate it and all that other stuff. Even if ...
- 444
3
votes
Accepted
SWR jumps to maximum of gauge
An antenna that's
Pretty short (0.08 wavelength),
Not tuned,
Mag-mounted to an inadequate counterpoise,
Indoors with who-knows-how-much metal in its near field,
could certainly have a 5:1 or worse ...
- 11.1k
2
votes
How should this SWR meter's directional coupler work?
C4/C5 form a capacitive voltage divider, L2 provides a DC return path for the meter current which needs to get back to the center tap to close that loop, and I suspect R2 lowers the Q of the ...
- 241
2
votes
How should this SWR meter's directional coupler work?
Simply put, if the current and voltage are in phase, the SWR should be relatively low. They will be in phase for a non-reactive load, i.e., a purely resistive load: a 50 ohm resistance with no ...
- 21
2
votes
How should this SWR meter's directional coupler work?
Incomplete answer — I still haven't figured this one out, but here's some leads/ideas I have so far.
I found a circuit with some similarities on Wikipedia called a single transformer hybrid coil:
It ...
- 7,104
2
votes
Is it possible to determine if I'm adjusting gamma match in correct direction with an SWR meter and if yes, how?
Well, I'm a little out of my depth, but this does seem to have all the usual parts of a gamma match: the matching section hanging off the main loop is a balanced transmission line, and the part ...
- 51.1k
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