Re: Making a Q-meter / References etc
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Rodger Bean
¿ªÔÆÌåÓýHi Dave, Thank you for the feedback, an amended version is attached. ?
Done. (Working in the TV broadcast industry, most of the transmitters that I worked on were 100W up to 30KW). ?
Done.
Done.
For dBu, use 600¦¸ and ignore Watts, dBm, dBmV & dbuV.
Just a personal preference. Re SI, having lived through: fps, cgs, MKS and SI. It¡¯s all just numbers, although at least in emu & esu (electrostatic units & electromagnetic units) there was no ¦Ð in a constant. And anyway, SI is just a collection of precisely defined, arbitrary units, relating to the an ordinary planet, orbiting around an ordinary star, in remote part of a galaxy that we call The Milky Way. They have as much in common with the rest of the universe as the distance from the thumb to the nose of whoever is the current reigning monarch. (lol). 7) If on the voltage gain section, I put an input of 1 V, and an output of -2 V, the calculator shows an error. Not so easy to fix, I could square V1 & V2 then square root them to remove the negative sign, but I don¡¯t believe that it is necessary.? And any changes that gave a negative dB would imply a loss where none exists. There may be a function that only takes the modulus of a number entry. But I think it would be easier to remember that you are using an inverting amplifier. * It's easy to configure an op-amp to have a negative gain (inverting amplifier). * A VNA will often measure a reflected voltage that is 180 degrees out of phase with respect to the input. ? Rodger Bean ? ? From: [email protected] <[email protected]> On Behalf Of Dr. David Kirkby, Kirkby Microwave Ltd
Sent: Tuesday, 30 August 2022 07:35 To: [email protected] Subject: Re: [Test Equipment Design & Construction] Making a Q-meter / References etc ? That's useful. Can I suggest a few improvements? ? 1) The input power of watt is rounded to the nearest integer - it would be useful if it allowed a few decimal places, as entering powers in nW or similar is not unusual. But if I enter 1.4 W, it gets rounded to 1 in the input display, but the outputs are more sensible. 2) You might consider whether it's worthwhile adding dbW. I know it's not used a lot, but our amateur licenses in the UK are specified in dBW now, not watt. 3) You say dBm is referenced to 1 mW, and dBuV is referenced to 1 uV, but for dBmV, you spell out the millivolt, rather than just put 1 mV. 4) You mention dBu, but don't allow anyone to perform any calculations with it. 5) There's a spelling error - impemdence 6) According to the BIPM, the body that defines the SI standards, virtually all SI units and derived units should be spelled in lower case, and without the s - so watt, ampere, volt, not Watts, Volts, Amps etc. I think the only exception to this is degrees Celsius. (I have attached a copy of the SI document). 7) If on the voltage gain section, I put an input of 1 V, and an output of -2 V, the calculator shows an error. * It's easy to configure an op-amp to have a negative gain (inverting amplifier). * A VNA will often measure a reflected voltage that is 180 degrees out of phase with respect to the input. ? I personally would take the absolute magnitudes of the voltages and use that to calculate the gain, so as to not show an error when the input and output are of a different sign. 8) According to the BIPM, there should be a space between a number and a unit - ie 2 uV not 2uV. 9) You are inconsistent in your use of P1 and P 1, and likewise V2 and V 2. Personally I would remove the spaces, as spaces imply multiplication. Or perhaps consider the use of subscripts. 10) I think the last part is potentially wrong, if the DUT does not accept all the input power. If the device reflects a lot of power on the left hand side, then the input power can be high, the output power low, but the dissipation is also low. When calculating antenna gains, the values are in terms of power accepted by the antenna, not the input power to the antenna. ? I can think of two things you could usefully add. 1) The ability to calculate output voltages given an input voltage and a gain. 2) Noise temperature to noise figure and noise factor conversions. ? It looks like a useful calculator, but there are some random suggestions of mine. ? Dave ? Dr David Kirkby Ph.D ? ? On Mon, 29 Aug 2022 at 20:45, Rodger Bean <rodgerbean@...> wrote:
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