20

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 circuitry that suggests this capability is flawed. We can show this empirically with two different experiments. Experiment 1 Connect a 100 ohm resistor directly ...


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 ...


10

I've not personally built antennas from scratch, but I appreciate my antenna analyzer just for being a good instrument — making the invisible aspects of my antenna system visible. Compared to using a SWR meter for the purpose, an antenna analyzer: Displays more information. A SWR meter still gives you enough information, in the sense that you can try ...


10

At power levels that low, you probably don't need an SWR meter permanently installed. You will find it useful to have an SWR meter or antenna analyzer available when building the antenna, though, to ensure it is properly operating on your chosen frequencies. Perhaps you can borrow one from a friend, mentor, or local radio club to use while building your kit?


10

A cross-meter is capable of showing you three measurements simultaneously: Output Power Reflected Power SWR From this image by Axel Schwenke on Wikipedia, you can see that the needle on the left indicates forward power, and the needle on the right indicates reflected power. The observed intersection of the two needles can be used to indicate the SWR of the ...


8

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 power only after measuring the SWR. Don't worry too much. If transmitting at much less than maximum power you won't damage anything even with the worst possible ...


7

(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 fixes for a similar bridge-circuit-based Arduino analyzer originally published in QST, November 2017. I realize I am a newcomer and many have already figured out ...


6

A properly calibrated cross-needle power meter such as e.g. the MFJ-842 actually tells you something more than just the forward and reflected power, which as you point out can just as easily be indicated by two separate instruments. The intersection of the needles gives you a pretty good indication of the actual standing wave ratio or SWR because the SWR is ...


5

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 magnitude of the reflection coefficient (Gamma), or MRC for short within the context of this answer. The MRC is the magnitude of the complex ratio of the reflected ...


5

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 exits port 1. This is expressed by the scattering matrix: $$ S={\begin{pmatrix}0&0&1\\1&0&0\\0&1&0\end{pmatrix}} $$ Or a 4 port ...


5

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 the problem known as “RF in the shack” — your transmitter's RF coming back to you on the outer shield of your feedline — then the metal will be RF-hot, but you ...


5

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 transceivers. A 100 watt transmitter could cause component failures within the meter. While the most likely result is simply the failure of the meter, I wouldn't ...


5

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 $Z_L$ and the characteristic impedance $Z_0$: $$ \Gamma = {Z_L - Z_0 \over Z_L + Z_0} $$ The reflection coefficient, like the load impedance, a complex number with ...


5

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 sockets, is 4" x 2" x 1". Here's the schematic. Tin plating is observed inside the enclosure. There is no PCB and the wiring is point-to-point. Connections to ...


5

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 is about 350-MHz, which seems too high. Tonne Software offers Diplexer Designer to address your requirement. Creating a low-pass / high-pass design with a ...


4

An antenna analyzer is not necessary. Sure, it's handy. A VNA is even handier. For this equipment you're looking at something like $50 USD for a NanoVNA, up to many thousands of dollars for a lab grade VNA. If you just want to know if you need to trim a bit off a wire dipole or not, and simply get on the air without toasting your transmitter, none of these ...


4

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 the end of the 1940's military surplus coaxial cable was hitting the ham market. Up to that point, ladder line was typically used for most ham antenna ...


4

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 or harmonic content of the transmitter output. The transmitter was a very basic VFO, buffer and a 6V6 RF final, maybe 3 or 4W RF output max. The antenna was ...


4

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 remnants of the switching frequency of the supply getting into your receiver and potentially interfering with desired signals or simply causing annoying tones (...


4

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 again to read the SWR. The calibrate procedure is to set the needle to the CAL position on the meter, not to the 100 watt reading as you described. Then flip ...


4

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 the antenna response is smooth. To make them smaller it helps to: increase the output power of the VNA reduce the measurement bandwidth turn on averaging. VNAs ...


4

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 favorable), and have not spent much time on the other bands. No tuner except for the built-in one on the IC-7300. With it in a less-than-ideal inverted V formation, ...


3

There are many ways you could calibrate. For measuring SWR, try this: Attach a 50Ω dummy load to your transmitter. The SWR should be 1:1. Then, attach two 50Ω dummy loads in parallel, giving you an effectively 25Ω load. The SWR should be 2. It seems you also want to measure power, and not just SWR. If you have some attenuators available, you can put them ...


3

I couldn't live without my two antenna analyzers -- I may even get a VNA (vector network analyzer) although that is not necessary for simple antenna analysis. I own both the MFJ 259B and the Autek Research RX Vector Analyst VA1. Although both do roughly the same thing, they have a few different features and I will touch on a few of those. Besides digital ...


3

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 circuit fits the bill. Testing with an SWR meter doesn't test the first, but it does test the second. That does mean the balun is doing at least half its job. ...


3

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 dummy load on 28 MHz, it will read ~50 ohms on the input because the SWR is 1:1. However, if I test it with a 600 ohm dummy load, it will read 5.8-j26 ohms on ...


3

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 defect. These should be determined from measurement, as actual lines can deviate significantly from published specifications and values can change as a result of ...


3

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 they do it, they may wonder if they did it right and if the reading will be accurate or not. I think you will need to handle this part in your design and ...


3

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 SWR, which is enough to "peg the needle" on most meters I've seen.


2

I've been a ham since 1963 and have built all my own antennas. Yagi beams—wire beams—loops—verts, etc. Back in those days all you had was a SWR bridge and maybe a grid dip meter. The most important thing, I think, is a booklet or some kind of articles on antenna design. They will give you accurate lengths and feed line info that should get you up and ...


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