Amateur Radio Stack Exchange
Amateur Radio Stack Exchange

Questions tagged [measurement]

60 questions
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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 whatever the feedpoint impedance was, the added…
Phil Frost - W8II
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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 with my HF radio. However, my test equipment at…
W5VO
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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 provide specific or useful information?
Adam Davis
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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.
Chris Pavey
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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 old phrasing. What's unclear to me is how they…
RoboKaren
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Ferrite rod or core 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 turns (same wire, just wind or unwind it) and…
Luca
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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 would then also be ground, and I may accidentally…
user885
7
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2 answers

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

Note: more measurements added after graphs below I recently acquired a RigExpert antenna analyzer and I am trying to learn how to use it to test cables. I took two cables to start with to try and understand what it shows and what the graphs mean. …
progrmr
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What exactly was a decremeter and how did they work?

In A Century of WWV, I found this mention of an unusual sounding instrument that may have once been commonplace: Calibration work was mainly focused on decremeters, instruments designed for measuring the decay, or decrement, of a pulsed radio…
natevw - AF7TB
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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 following. I can wind a 1:1 transformer using this…
Aleksander Alekseev - R2AUK
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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 supposed to happen. So now I need to figure out what…
natevw - AF7TB
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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 overkill", "design X could lead to spurious…
natevw - AF7TB
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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 snipping radials because I really don't know if the…
David Hoelzer
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Can an oscilloscope be used as an RF voltmeter?

I just recently acquired a slightly functional Icom IC-735 HF radio, and am trying to resurrect it. The service manual outlines procedures that specify the use of an RF Voltmeter, which I do not own. I do have a Tektronix 2236 dual channel 100MHz…
user14945
5
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1 answer

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 calibration, I would expect to have a return loss of 0dB…
Dieter Vansteenwegen ON4DD
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