Questions tagged [measurement]

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4
votes
0answers
46 views

How to measuring ferrite core efficiency vs frequency

There is an unknown ferrite toroid. I would like to figure out whether it can be used in an audio transformer, or maybe in a 1:4 transformer on given HF frequency. The experiment I came up with is ...
2
votes
1answer
53 views

Measurements in far field for radar cross section

I have to measure the S parameter for a rectangular sample with an antenna that works from 2 to 18 GHz. I need to measure a large band from 5 to 15 GHz and I have a problem with the known F.F. (Far ...
1
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0answers
59 views

Parasitic inductance of relay contacts

I need to switch a bank of filters operating on bands from about 2MHz to 30MHz. The parasitic series inductance of the relay contact system will have an effect on the performance of my system. ...
5
votes
3answers
277 views

Determining Impedance With An Antenna Analyzer

I need some help interpreting some information from my antenna analyzer (RigExpert AA-35). I want to use the information to impedance match my AM receiving antenna system to AM radios. No ...
1
vote
1answer
101 views

Cabling question between two devices

Here is my schema. I would like to connect a device using SMA connector with RG 174 to an attenuator of 30 dB with SMA connector. On the other side the attenuator is connected to a SMA-UHF converter ...
1
vote
1answer
52 views

Measuring S21 against TX-RX distance (a.k.a path loss modelling) with a network analyzer didn't give expected results

Task: Path loss modelling Target frequency: 433 MHz; Laboratory environment: in a basement where there were other equipment and metal shelves. A few acoustic absorbers were placed around the setup. ...
5
votes
2answers
320 views

dBm signal minus dB

I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm? I've tried Googling that without any luck.
1
vote
1answer
61 views

How to measure the power emitted from an HF antenna in near-field WPT?

I'd like to estimate the power density from a 13.56 MHz power source in a near-field WPT (wireless power transfer) scenario. Using a spectrum analyzer with a receiving antenna will give the E-field ...
5
votes
1answer
52 views

What is the best approach for measuring return loss of a home-made 3cm horn?

Let's assume I have built a SMA-to-waveguide transition that flares out into a horn antenna. There's no flange between transition and horn, it's made of a single metal sheet. The antenna has tuning ...
2
votes
1answer
52 views

Wire dipole antenna proving ground / test bench

i am considering building two movable (concrete base with wheels) non metallic poles with hooks every ten centimeters or so, in order to test wire dipoles of various sizes at various heights with an ...
0
votes
2answers
129 views

Peak envelope power should be 2:1 or 4:1 on meter?

I've always been reading my AM modulated signal on a Bird wattmeter and trying to set the carrier to 1/4 of the peak envelope power (PEP). Recently, I was told by a CBer that you only can see it that ...
3
votes
2answers
130 views

Antenna design - Ground plane in simulation and in practice

For monopole antennas, the ground plane acts as another arm of an equivalent dipole antenna. I'm wondering how we can expect the behavior of that antenna in practice, because the ground plane is ...
4
votes
1answer
67 views

Why is the insertion loss of my coax cable higher than expected?

I am testing a long cable run (about 90m). This cable has been used outside and inside, for temporary setups. I've set up my VNA with the correct values (velocity factor,...) and the distance to ...
8
votes
2answers
203 views

How were 1920s hams able to measure megahertz frequency?

I was reading 200 Meters and Down but one thing that was unclear to me was that hams in the 1920s were operating on the 200 meter frequency, which is around 1.5 Mhz .... or 1500 kilocycles to use the ...
0
votes
1answer
720 views

Input and output impedance of antenna/circuit: theory and measurement methods?

As illustrated in my previous post, I got stuck with the matching circuit between an receiving antenna and my circuit, including a rectifier and sensory circuits. I got confused with input and output ...
2
votes
1answer
62 views

How should I measure RFI on the headset cable from a hand-talkie?

I'd like to build an audio interface cable from my smartphone to my Yaesu FT-60 which incorporates VOX (since the Yaesu doesn't have VOX functionality) for APRS apps on the phone. I'm having problems ...
2
votes
2answers
123 views

Measuring dBs with software defined radio

If the "floor" of the graph in my SDR is at -110dB, and when I key up, it goes to -70dB, and the wattage is 5W....is there a direct correlation between dBs and wattage?
3
votes
1answer
252 views

Seeming conflict in the definitions of dynamic range

As I understand it, dynamic range is the difference in dB between the strongest and weakest signal discernible by your receiver. So, the larger the dynamic range, the better, which seems intuitive. ...
5
votes
2answers
295 views

Ferrite rod permeability determination

Is there a simple empiric way of determining the permeability (mhu) of a ferrite object (be it a ring, rod or any form)? I've been thinking this for a rod: if I wind coils with different number of ...
3
votes
1answer
567 views

How to probe a dipole antenna?

I want to start experimenting and tinkering with antennas, starting with ½ wave dipoles. I will be measuring the AC voltages on both the transmitter and the reciever antennas simultaneously. And by ...
3
votes
2answers
386 views

Is it possible to measure antenna trap with MFJ225 without help of PC?

I have MFJ225 antenna analyzer. I measure coax trap filters by connecting this analyzer to PC and using IG_miniVNA application. That works fine. But, sometimes I need to make such measurements in ...
1
vote
1answer
459 views

Why Coaxial Collinear Antenna Gives Strange Graph of Frequency Sweep vs SWR?

Antenna Analyzer gives a understandable results for a Quad Antenna (photos 1, 2 & 3), but gives strange results for Coaxial Collinear Antenna (photo 4) Photo 1 of 4: Test setup for Quad Antenna ...
2
votes
1answer
60 views

crt TV emissions

I have my Hack RF plugged in my TV antenna to have a cheap setup and I have observed on the spectrum analyser a signal (Bandwidth: ~400Khz) that is emitted by my old analog TV from 80ies. These are my ...
5
votes
1answer
115 views

Measurement/calibration error after OSL calibration on VNA

Purchased a HP 8711A some time ago to learn how to make better measurements. I've tried doing an OSL calibration with a 75ohms Agilent cal kit. When reconnecting the short after succesful ...
2
votes
1answer
104 views

Portable radio antenna measurement

Just purchased a HP 8711A and have "upgraded" the bootrom to enable vector measurements. I am now trying to learn more about how to make better measurements and understand what's going on. One of the ...
2
votes
1answer
588 views

Measuring energy density of 2.4 GHz and 5.0 GHz signals

I'm a math and computer science student, starting to mess around with using amplifiers and antennas to build long-range wifi hardware in my spare time. Calculating the expected power density of a ...
5
votes
3answers
3k views

How should this SWR meter's directional coupler work?

I'm wrapping up a "home build" of the MFJ-941EK antenna tuner kit and having trouble getting the wattmeter calibrated. I can't use C4 to get the reflected power reading calibrated down to 0 as is ...
5
votes
4answers
472 views

Recommended way to analyze spectrum output of a high-power amplifier?

I have a small collection of "software defined RF lab" equipment, notably a HackRF and a VNWA3. I am almost done building a 35W HF amplifier and once I've done some other testing, would like to look ...
1
vote
2answers
221 views

Rudementary Impedance measurements for VLF antenna system

I am looking for ideas to improve my Impedance measurements I perform on my VLF antenna system. Due to circumstances my VLF experiments are usually "on location / in a field" so I do not have the ...
3
votes
2answers
2k views

How to measure a balun for effectiveness?

It seems there are almost as many "balun" designs as there are web pages about "baluns". There's lots of accusations pointed in all directions ("design Z isn't a balun OR a choke", "design Y is ...
1
vote
1answer
119 views

If i measure a rf source as 20 dBm in spectrum analyser inline with 20db attenuator, what is the actual power generated by rf sorce

Measurement 20dbm + 20 db attenuator, what is the actual power of rf source
3
votes
2answers
3k views

Tuning/trimming a ground plane antenna

I've built a ground plane antenna with a 19.5" vertical and 4 20" radials. Currently, at 147.135 MHz my SWR is 3:1, clearly not ideal (and even bad for the transmitter!). I'm reluctant to start ...
6
votes
1answer
925 views

Can I touch the ground of a PWR/SWR meter?

I'm planning to build a 5W PWR/SWR meter very similar to this design by G3YMC, but with two meters: I'd like to put it in this metal box, and use the box as ground. However, the bottom of the box ...
10
votes
4answers
891 views

How does an antenna transform impedances along its length?

If I insert some impedance (like a loading coil, or a trap) at the base of a monopole antenna, the effect on the feedpoint impedance is easy to predict: the impedance is in series with the antenna, so ...
2
votes
1answer
8k views

Measuring RF voltages with a multimeter

Is it possible to measure RF voltages with a multimeter? I have a multimeter which can measure AC voltages up to 600V RMS, but I'm not sure because I don't know if it assumes the signal to be 50Hz, or ...
1
vote
1answer
90 views

Is it possible to measure the capacitance of a gamma rod? Gamma match

I was wondering if it is possible to measure the capacitance of a gamma rod using an L/C meter. I tried to measure one by clipping one of the alligator clips on the outer aluminum tube and the other ...
9
votes
2answers
4k views

How can I calibrate a SWR meter?

I would like to build my own HF (1.8 - 30 MHz) SWR meter, however I'm not sure how I can calibrate the meter without an accurate power source. I'm targeting a power capacity of 150 W so I can use it ...
2
votes
2answers
162 views

Measuring antenna characteristics without physical access?

There is a loop antenna that was thrown around an attic interior several decades ago, of long forgotten dimensions. I found the feed line. Is there a way to measure what (U.S. amateur) bands on ...
8
votes
2answers
865 views

What is the point of a SWR/power meter where the needles cross over each other?

There are SWR/power meters with two separate gauges, and others that have them mounted so the gauge needles cross over each other. Aside from looking cool, does the cross-over point of the two meters ...