Re: NanoVNA Under The Covers
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Yes of course, but all RLBs will give an absolute value of k plus the actual return loss of the DUT. For 50 ohm source and detectors this constant is theoretically 12.09dB but in reality changes with loads and frequency. Part of the calibration process is to eliminate this constant. In practice it also eats into the dynamic range of the generator and detector. So to measure a max of X dB will require borh generator and detector to have X +12dB, assuming the bridge was calibrated with a load that is better than or equal to XdB max in the first place.Sent from my Samsung Galaxy smartphone.
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-------- Original message --------From: "Stuart Landau via Groups.Io" <stuartl73@...> Date: 05/08/2019 23:24 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers An opencircuit on a transmission line has infinite impedance. A short circuit has zeroimpedance. An opencircuit,short circuit, or pure reactance terminating a transmission line are incapableof absorbing power fromaforward, or incident, wave. Thus, all incident current and voltage arereflected back toward the source.When this condition occurs,the return loss is said to be 0 dB.?The source:? ttps://www.scte.org/TechnicalColumns/05-10-01%20return%20loss.pdf?If you are measuring the return loss of a device with some attenuation in the path, such as coaxial cable losses, the return loss will be twice the cable loss because the RF travels twice through the attenuation. The first is the incidence wave, the second the reflected wave. The more attenuation in the path, the better the load looks; but it isn't telling you the truth with regard to the device under test.Stuart K6YAZ?Los Angeles, USA-----Original Message-----From: tuckvk3cca <tuckvk3cca@...>To: nanovna-users <[email protected]>Sent: Mon, Aug 5, 2019 1:29 pmSubject: Re: [nanovna-users] NanoVNA Under The CoversNo the return loss of open and short is theoretically 12dB. The RLB has a voltage factor of 8 and the transmission has a factor of 2 .?Sent from my Samsung Galaxy smartphone.-------- Original message --------From: Jeff Anderson <jca1955@...> Date: 05/08/2019? 21:26? (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers On Mon, Aug? 5, 2019 at 10:06 AM, tuckvk3cca wrote:>> You measure an open load, you measure a shorted load both of which should give> 12dB return loss>I'm probably missing something here, but shouldn't opens and shorts give 0 dB of return loss, not 12?? After all, their Gamma ought to be equal to 1.- Jeff, k6jca
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