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How to measure induced coupling RF between two antennas
#measurement
#nanovna-h4
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Marv
I am trying to use my NanoVNA-H to see how much near-field coupling I have between two antennas in my backyard that are about 10 feet apart. I have one antenna connected to the S11 port and the other to the S21 port. I have S11 set to SWR and S21 set to LOGMAG. LOGMAG is -53dB at the point in the graph that both lines cross. I assume that is the amount of power being induced in the antenna connected to S21 by the antenna connected to S11.
Since the NanoVNA is only putting out a small amount of RF power, how would I relate that to for example transmitting 25 watts on one of these antennas and determining how much power is being induced in the other antenna? |
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That would be 25 Watts minus 53 dB.
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25 watts is 44 dBm 44 - 53 = -9 dBm? ?Or about? 1/10th milliwatt Now you know why they like to keep the loops REAL close for inductive charging. Kent WA5VJB On Thursday, June 30, 2022, 07:47:39 AM CDT, Marv <m207365@...> wrote:
I am trying to use my NanoVNA-H to see how much near-field coupling I have between two antennas in my backyard that are about 10 feet apart. I have one antenna connected to the S11 port and the other to the S21 port. I have S11 set to SWR and S21 set to LOGMAG. LOGMAG is -53dB at the point in the graph that both lines cross. I assume that is the amount of power being induced in the antenna connected to S21 by the antenna connected to S11. Since the NanoVNA is only putting out a small amount of RF power, how would I relate that to for example transmitting 25 watts on one of these antennas and determining how much power is being induced in the other antenna? |
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Hello Marv,
I can tell by reading your question that some of your understanding of how the Nano VNA works is not clear. First the Nano VNA has two connectors they are referred to as Channel0 and Channel1 The Nano VNA has two operation modes, Refection and Thru Cannel0 is used for reflection mode measurements Channel0 and channel1 are used for thru mode measurements Think of the two antennas as a two-port network. Measuring the insertion loss (S21) between the two antennas will give you the coupling from one to the other. You only need the display set up for LogMag There is no crossing of one trace to the other. The LogMag trace gives you the coupling between the antennas as a function of frequency. I assume you are doing the correct frequency start stop set up and a full SOLT calibration The previous reply showed you how to calculate the amount of power induced into the second antenna when 25 watts is present on the first one Hope this helps clear up things for you. 73 Greg WA1JXR |
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Hi Marv,
The previous reply showed you that the signal level in the second antenna would be -9 dBm. Normal signal level calibration for a receiver is a S9 signal is 50 microvolts at the antenna, in dBm this is -73 dBm. Your signal level of -9 dBm is 64 dB above that. That would read S9+64dB on you S meter. Some S meters read S9+40 some S9+60. This would be full scale on you S meter and more. This may be close to the receiver overload point. If your receiver has built in attenuator, I would select 20dB or 40 dB or more to get the signal to where the receiver can comfortably handle it. Hope this helps 73 Greg WA1JXR |
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Much more than +64 dBm and you are very close to digital saturation on the
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A/D. Personally, I wouldn't go there without at least a 20 dB attenuator inline. Of course, that will also decrease your general received signals by 20 dB. Dave - W?LEV On Thu, Jun 30, 2022 at 2:12 PM wa1jxr <wa1jxr@...> wrote:
Hi Marv,-- *Dave - W?LEV* *Just Let Darwin Work* --
Dave - W?LEV |
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Marv, not a bad idea to use separate antennas for Tx and Rx. Makes QSK CW possible and easy, but: 1) use a fast QSK TR switch on the receiving antenna to disconnect it and ground the receive input during Tx cycles; 2) separate the 2 antennas as far as possible; 3) use opposite polarities for the 2 antennas -- vertical for one, horizontal for the other -- Rich------ Original message------From: MarvDate: Thu, Jun 30, 2022 1:03 PMTo: [email protected];Cc: Subject:Re: [nanovna-users] How to measure induced coupling RF between two antennas #measurement #nanovna-h4Well my original goal was to determine if it was safe to use both antennas at the same time (one TX- one RX) on two different radios. I can see that would not be wise. Thanks for all the help. Can't learn anything without asking dumb questions!
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Did a coupling test between two antennas and it was interesting to see how the impedance looking into one antenna was impacted when leaving one of the antennas open, shorted and terminated in 50 ohms. With about 28 dB between antennas I would see a change of a about 0.5 to 1 ohm. Could be an indication of how one antenna impacts the radiation pattern of the other. The energy reflected by one of the antennas is phase shifted by 180 degrees between a short and an open condition. At 28 dB of isolation I bet there is little pattern change. Something to think about.
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One seldom achieves the "advertised" or modeled pattern, especially at HF
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frequencies. VHF, UHF, and ?waves are whole different stories. HF patterns rarely conform to expected results except for installations done by Uncle with unlimited budget (just us taxpayers!). So, don't sweat the pattern modification. Even the "expected" pattern is likely not thereas assumed. And with only 28 dB isolation between the two antennas, disconnect one from any receivers while transmitting on the other. 28 dB down from 100-watts is still roughly 160 mW. I sure would not input that much power into any receiver I own! Dave - W?LEV On Sat, Jul 2, 2022 at 7:15 PM WB2UAQ <pschuch@...> wrote:
Did a coupling test between two antennas and it was interesting to see how-- *Dave - W?LEV* *Just Let Darwin Work* --
Dave - W?LEV |
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