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I read -70 dB also on two different NanoVnas. Ch0 LogMag @ 50 KHz using the 50 Ohm load that came with the NanoVna. This is the same 50 Ohm that was used in the calibration. The calibration procedure assumes the load to be perfect so return loss shows 70 dB. It goes up with Frequency but is always better than -50 dB.

Jim K.

It is repeatable. It always shows 70 dB with that same load.

Thanks Gary. I contacted my supplier, EBay and ask if I could get another
set of cal8bration loads.? No luck. The 50 ohm was of very high quality,
return loss -70dB compared to -40dB from another source I had, up to 1GHz.
Anyone knows where to get such loads? Sent from my Samsung Galaxy
smartphone.

- r {\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}I
-
I suppose we could start a fight over this, but here is what Wikipedia has to say about the sign of return loss. There is no claim made that this is "the last word" on this subject. I learned to use a negative sign a long time ago.

Sign[edit]
Properly, loss quantities, when expressed in decibels, should be positive numbers.[note 1] However, return loss has historically been expressed as a negative number, and this convention is still widely found in the literature.[1]The correct definition of return loss is the difference in dB between the incident power sent towards the Device Under Test (DUT) and the power reflected, resulting in a positive sign:
- R L ( d B ) = 10 log 10 ? P i P r {\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}}
However taking the ratio of reflected to incident power results in a negative sign for return loss;
- R L ′ ( d B ) = 10 log 10 ? P r P i {\displaystyle RL'(\mathrm {dB} )=10\log _{10}{P_{\mathrm {r} } \over P_{\mathrm {i} }}}
- where RL'(dB) is the negative of RL(dB).
Return loss with a positive sign is identical to the magnitude of Γ when expressed in decibels but of opposite sign. That is, return loss with a negative sign is more properly called reflection coefficient.[1] The S-parameter S11 from two-port network theory is frequently also called return loss,[2] but is actually equal to Γ.Caution is required when discussing increasing or decreasing return loss since these terms strictly have the opposite meaning when return loss is defined as a negative quantity.
Stuart Landau K6YAZLos Angeles, USA
-----Original Message-----
From: Dr. David Kirkby from Kirkby Microwave Ltd <drkirkby@...>
To: nanovna-users <[email protected]>
Sent: Sun, Aug 4, 2019 8:29 am
Subject: Re: [nanovna-users] NanoVNA Under The Covers

On Sun, 4 Aug 2019 at 08:46, tuckvk3cca <tuckvk3cca@...> wrote:

Thanks Gary. I contacted my supplier, EBay and ask if I could get another
set of cal8bration loads.? No luck. The 50 ohm was of very high quality,
return loss -70dB compared to -40dB from another source I had, up to 1GHz.
Anyone knows where to get such loads? Sent from my Samsung Galaxy
smartphone.

Return loss of loads should not stated as a *positive* number as it’s a
loss. A return loss with a negative number could only be obtained from a
negative resistance, such as a Gunn diode amplifier.

A return loss of 70 dB can only found in fairyland! I measured 44 dB, but
stated that the measurement would be subject to large errors as the return
loss of the loads in my 85052B calibration kit were specified as 48 dB.
Really, 70 dB can only be found in fairyland. Another VNA might indicate 70
dB, but the result is meaningless.

Dave G8WRB

? ?
? ? ? ? - r? ? ? ? {\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}I
? ?
? ? -
I suppose we could start a fight over this, but here is what Wikipedia has to say about the sign of return loss. There is no claim made that this is "the last word" on this subject. I learned to use a negative sign a long time ago.

Sign[edit]
Properly, loss quantities, when expressed in decibels, should be positive numbers.[note 1] However, return loss has historically been expressed as a negative number, and this convention is still widely found in the literature.[1]The correct definition of return loss is the difference in dB between the incident power sent towards the Device Under Test (DUT) and the power reflected, resulting in a positive sign:
? ? ? ? -? ? R L (? d B? ) = 10? log? 10? ?? ? P? i? ? P? r? ? ? ? {\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}}
However taking the ratio of reflected to incident power results in a negative sign for return loss;
? ? ? ? -? ? R? L ′? (? d B? ) = 10? log? 10? ?? ? P? r? ? P? i? ? ? ? {\displaystyle RL'(\mathrm {dB} )=10\log _{10}{P_{\mathrm {r} } \over P_{\mathrm {i} }}}
? ? ? ? - where RL'(dB) is the negative of RL(dB).
Return loss with a positive sign is identical to the magnitude of Γ when expressed in decibels but of opposite sign. That is, return loss with a negative sign is more properly called reflection coefficient.[1] The S-parameter S11 from two-port network theory is frequently also called return loss,[2] but is actually equal to Γ.Caution is required when discussing increasing or decreasing return loss since these terms strictly have the opposite meaning when return loss is defined as a negative quantity.
Stuart Landau K6YAZLos Angeles, USA
-----Original Message-----
From: Dr. David Kirkby from Kirkby Microwave Ltd <drkirkby@...>
To: nanovna-users <[email protected]>
Sent: Sun, Aug 4, 2019 8:29 am
Subject: Re: [nanovna-users] NanoVNA Under The Covers

On Sun, 4 Aug 2019 at 08:46, tuckvk3cca <tuckvk3cca@...> wrote:

Thanks Gary. I contacted my supplier, EBay and ask if I could get another
set of cal8bration loads.? No luck. The 50 ohm was of very high quality,
return loss -70dB compared to -40dB from another source I had, up to 1GHz.
Anyone knows where to get such loads? Sent from my Samsung Galaxy
smartphone.

Return loss of loads should not stated as a *positive* number as it’s a
loss. A return loss with a negative number could only be obtained from a
negative resistance, such as a Gunn diode amplifier.

A return loss of 70 dB can only found in fairyland! I measured 44 dB, but
stated that the measurement would be subject to large errors as the return
loss of the loads in my 85052B calibration kit were specified as 48 dB.
Really, 70 dB can only be found in fairyland. Another VNA might indicate 70
dB, but the result is meaningless.

Dave G8WRB