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RTL SDR Input Impedance


Esteban H 2021/07/03 19:24

Has anyone tried to measure the input impedance of any SDR Dongle using a
Nano VNA?

Regards.

Siegfried Jackstien 2021/07/04 19:05

i would never try that ... 10mw into the antenna socket will kill your sdr

dg9bfc sigi

Am 03.07.2021 um 20:24 schrieb Esteban H:

Jim Lux 2021/07/04 10:22

On 7/4/21 10:05 AM, Siegfried Jackstien wrote:
>
> i would never try that ... 10mw into the antenna socket will kill your sdr
>
> dg9bfc sigi
>

perhaps not - there's protection diodes on the front of the RTL-SDR and
the R820T input chip might tolerate +10dBm no damage


https://www.rtl-sdr.com/wp-content/uploads/2013/04/R820T_datasheet-Non_R-20111130_unlocked1.pdf
doesn't give a max, but


https://www.onesdr.com/2020/01/29/how-not-to-break-your-software-defined-radio-hardware/
gives the following table (without saying where they got the numbers)

*HackRF <https://amzn.to/3ccMZ2e>* – 5 dBm 0.3 milliwatt
*RTL-SDR <https://amzn.to/3ies9mz>* +10 dBm 10 milliwatt
*ADALM Pluto <https://amzn.to/3yQLmke>* +2.5 dBm 1.8 milliwatt
BladeRF +2.5 dBm 1.8 milliwatt
*SDRplay RSP1A <https://amzn.to/3pqMPcZ>* 0 dBm 1 milliwatt

Siegfried Jackstien 2021/07/04 19:43

ok .. the rtl dongle may be safe ... but others not

maybe you can measure them when you add an attenuator in line (and
calibrate WITH attenuator)

how accurate that will be?? no idea ...

what does the input impedance tell you??

for me on sdrs most needed values are ... sensitivity and dynamic range
... but not the input impedance

if you want to add filters in line ... and filter responce does change
with receivers impedance ... ok then it will play a role

greetz sigi dg9bfc

Am 04.07.2021 um 19:22 schrieb Jim Lux:

Jos Stevens 2021/07/04 20:17

Hi,

When you put an attenuator on the input of the SDR, tmho you will not
measure ihe input impedance of the SDR, but of the attenuator,  more or
less.

Jos

Op 4-7-2021 om 19:43 schreef Siegfried Jackstien:
> ok .. the rtl dongle may be safe ... but others not
>
> maybe you can measure them when you add an attenuator in line (and
> calibrate WITH attenuator)
>
> how accurate that will be?? no idea ...
>
> what does the input impedance tell you??
>
> for me on sdrs most needed values are ... sensitivity and dynamic
> range ... but not the input impedance
>
> if you want to add filters in line ... and filter responce does change
> with receivers impedance ... ok then it will play a role
>
> greetz sigi dg9bfc
>
> Am 04.07.2021 um 19:22 schrieb Jim Lux:
>> On 7/4/21 10:05 AM, Siegfried Jackstien wrote:
>>>
>>> i would never try that ... 10mw into the antenna socket will kill
>>> your sdr
>>>
>>> dg9bfc sigi
>>>
>>
>> perhaps not - there's protection diodes on the front of the RTL-SDR
>> and the R820T input chip might tolerate +10dBm no damage
>>
>>
>> https://www.rtl-sdr.com/wp-content/uploads/2013/04/R820T_datasheet-Non_R-20111130_unlocked1.pdf
>> doesn't give a max, but
>>
>>
>> https://www.onesdr.com/2020/01/29/how-not-to-break-your-software-defined-radio-hardware/
>> gives the following table (without saying where they got the numbers)
>>
>> *HackRF <https://amzn.to/3ccMZ2e>*     – 5 dBm     0.3 milliwatt
>> *RTL-SDR <https://amzn.to/3ies9mz>*     +10 dBm     10 milliwatt
>> *ADALM Pluto <https://amzn.to/3yQLmke>*     +2.5 dBm 1.8 milliwatt
>> BladeRF     +2.5 dBm     1.8 milliwatt
>> *SDRplay RSP1A <https://amzn.to/3pqMPcZ>*     0 dBm     1 milliwatt
>>
>>
>>
>>
>>
>>
>>
>>
>
>
>
>
>

--
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Siegfried Jackstien 2021/07/04 20:26

if you calibrate the vna WITH attenuator it should be calculated out
(more or less) ... not?!?

it is "nearly" the same as when you measure with a vna over a longer
cable (that also has loss plus shifts the phase and reverts impedance
every quarterwave)

calibrating should take care of that

dg9bfc sigi

Am 04.07.2021 um 20:17 schrieb Jos Stevens:

David Eckhardt 2021/07/04 18:40

Here is a section of the AirSpy R2 specifications. Note the max input RF
is +10 dBm (10 mW):
[image: image.png]
The NANOs can be set for less than 0 dBm output which certainly will not
damage the input preamp. HOWEVER, that level will likely put the input
stage into saturation where a faithful measurement of the input Z will not
be possible. When measuring preamps I usually stick to something less than
-45 dBm (-20 dBm from the TG and 25 dB attenuator) to be sure I'm not
driving the amp into non-linear regions where measurements do not reflect
normal operation.

Dave - WØLEV

On Sun, Jul 4, 2021 at 6:17 PM Jos Stevens <jrs@xs4all.nl> wrote:

> Hi,
>
> When you put an attenuator on the input of the SDR, tmho you will not
> measure ihe input impedance of the SDR, but of the attenuator, more or
> less.
>
> Jos
>
> Op 4-7-2021 om 19:43 schreef Siegfried Jackstien:
> > ok .. the rtl dongle may be safe ... but others not
> >
> > maybe you can measure them when you add an attenuator in line (and
> > calibrate WITH attenuator)
> >
> > how accurate that will be?? no idea ...
> >
> > what does the input impedance tell you??
> >
> > for me on sdrs most needed values are ... sensitivity and dynamic
> > range ... but not the input impedance
> >
> > if you want to add filters in line ... and filter responce does change
> > with receivers impedance ... ok then it will play a role
> >
> > greetz sigi dg9bfc
> >
> > Am 04.07.2021 um 19:22 schrieb Jim Lux:
> >> On 7/4/21 10:05 AM, Siegfried Jackstien wrote:
> >>>
> >>> i would never try that ... 10mw into the antenna socket will kill
> >>> your sdr
> >>>
> >>> dg9bfc sigi
> >>>
> >>
> >> perhaps not - there's protection diodes on the front of the RTL-SDR
> >> and the R820T input chip might tolerate +10dBm no damage
> >>
> >>
> >>
> https://www.rtl-sdr.com/wp-content/uploads/2013/04/R820T_datasheet-Non_R-20111130_unlocked1.pdf
> >> doesn't give a max, but
> >>
> >>
> >>
> https://www.onesdr.com/2020/01/29/how-not-to-break-your-software-defined-radio-hardware/
> >> gives the following table (without saying where they got the numbers)
> >>
> >> *HackRF <https://amzn.to/3ccMZ2e>* – 5 dBm 0.3 milliwatt
> >> *RTL-SDR <https://amzn.to/3ies9mz>* +10 dBm 10 milliwatt
> >> *ADALM Pluto <https://amzn.to/3yQLmke>* +2.5 dBm 1.8 milliwatt
> >> BladeRF +2.5 dBm 1.8 milliwatt
> >> *SDRplay RSP1A <https://amzn.to/3pqMPcZ>* 0 dBm 1 milliwatt
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >
> >
> >
> >
>
> --
> Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware.
> https://www.avast.com/antivirus
>
>
>
>
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

Jos Stevens 2021/07/04 21:00

When you calibrate WITH the attenuator you calculate out the attenuation
, but you are no more measuring the imput impedance of the connected
device, am I wrong ?

Jos


Op 4-7-2021 om 20:26 schreef Siegfried Jackstien:
> if you calibrate the vna WITH attenuator it should be calculated out
> (more or less) ... not?!?
>
> it is "nearly" the same as when you measure with a vna over a longer
> cable (that also has loss plus shifts the phase and reverts impedance
> every quarterwave)
>
> calibrating should take care of that
>
> dg9bfc sigi
>
> Am 04.07.2021 um 20:17 schrieb Jos Stevens:
>> Hi,
>>
>> When you put an attenuator on the input of the SDR, tmho you will not
>> measure ihe input impedance of the SDR, but of the attenuator,  more
>> or less.
>>
>> Jos
>>
>> Op 4-7-2021 om 19:43 schreef Siegfried Jackstien:
>>> ok .. the rtl dongle may be safe ... but others not
>>>
>>> maybe you can measure them when you add an attenuator in line (and
>>> calibrate WITH attenuator)
>>>
>>> how accurate that will be?? no idea ...
>>>
>>> what does the input impedance tell you??
>>>
>>> for me on sdrs most needed values are ... sensitivity and dynamic
>>> range ... but not the input impedance
>>>
>>> if you want to add filters in line ... and filter responce does
>>> change with receivers impedance ... ok then it will play a role
>>>
>>> greetz sigi dg9bfc
>>>
>>> Am 04.07.2021 um 19:22 schrieb Jim Lux:
>>>> On 7/4/21 10:05 AM, Siegfried Jackstien wrote:
>>>>>
>>>>> i would never try that ... 10mw into the antenna socket will kill
>>>>> your sdr
>>>>>
>>>>> dg9bfc sigi
>>>>>
>>>>
>>>> perhaps not - there's protection diodes on the front of the RTL-SDR
>>>> and the R820T input chip might tolerate +10dBm no damage
>>>>
>>>>
>>>> https://www.rtl-sdr.com/wp-content/uploads/2013/04/R820T_datasheet-Non_R-20111130_unlocked1.pdf
>>>> doesn't give a max, but
>>>>
>>>>
>>>> https://www.onesdr.com/2020/01/29/how-not-to-break-your-software-defined-radio-hardware/
>>>> gives the following table (without saying where they got the numbers)
>>>>
>>>> *HackRF <https://amzn.to/3ccMZ2e>*     – 5 dBm     0.3 milliwatt
>>>> *RTL-SDR <https://amzn.to/3ies9mz>*     +10 dBm     10 milliwatt
>>>> *ADALM Pluto <https://amzn.to/3yQLmke>*     +2.5 dBm 1.8 milliwatt
>>>> BladeRF     +2.5 dBm     1.8 milliwatt
>>>> *SDRplay RSP1A <https://amzn.to/3pqMPcZ>*     0 dBm 1 milliwatt
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>
>>>
>>
>
>
>
>
>

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Esteban H 2021/07/04 21:01

Ok, but an attenuator could be used then. I will calculate in my case the
needed attenuation.

Thanks.

El dom., 4 jul. 2021 18:06, Siegfried Jackstien <
siegfried.jackstien@freenet.de> escribió:

John Gord 2021/07/04 13:33

Jos,
Doing the "open, short, load" calibration at the attenuator output allows the VNA to do the math to figure out the unknown impedance connected at that point.  The cost is in dynamic range:  The test signal is attenuated both on the way out and on the way back in.  Adding a 10dB attenuator increases the noise of the measurement by something like 20dB.
--John Gord

On Sun, Jul 4, 2021 at 12:00 PM, Jos Stevens wrote:

Esteban H 2021/07/04 21:37

Interesting point. Thus, attenuation cannot be arbitrary high, it can be
selected to do not damage SDR at the same time we keep in the dynamic range
of the NVNA for a coherent measurement.

Thanks.

El dom., 4 jul. 2021 21:34, John Gord via groups.io <johngord=
verizon.net@groups.io> escribió:

Clifford Heath 2021/07/04 15:02

The HackRF is very vulnerable, but the data given in the article at onesdr is incorrect. The most common damage is to the LNA, which has a damage level of 13dBm. Other paths are less vulnerable. I designed a protected version with effective limiting diodes, and none of those is units (over 1000 so far) has been reported to have been damaged, compared more than one in ten of the original type.

Jos Stevens 2021/07/05 00:32

Hi John,

I  never have thought that the VNA calculated back the  impedance at the
end of the attenuator, when I measure an RF amplifier of eg 20dB,  I
always put an attenuator of at least 20dB's in front, I'm afraid the
accuracy of the impedance measurement will be poor then.

Thanks for your reply,

Jos


Op 4-7-2021 om 22:33 schreef John Gord via groups.io:
> Jos,
> Doing the "open, short, load" calibration at the attenuator output
> allows the VNA to do the math to figure out the unknown impedance
> connected at that point.  The cost is in dynamic range:  The test
> signal is attenuated both on the way out and on the way back in.
> Adding a 10dB attenuator increases the noise of the measurement by
> something like 20dB.
> --John Gord
>
> On Sun, Jul 4, 2021 at 12:00 PM, Jos Stevens wrote:
>
> When you calibrate WITH the attenuator you calculate out the
> attenuation
> , but you are no more measuring the imput impedance of the connected
> device, am I wrong ?
>
> Jos
>
>
> Op 4-7-2021 om 20:26 schreef Siegfried Jackstien:
>
> if you calibrate the vna WITH attenuator it should be
> calculated out
> (more or less) ... not?!?
>
> it is "nearly" the same as when you measure with a vna over a
> longer
> cable (that also has loss plus shifts the phase and reverts
> impedance
> every quarterwave)
>
> calibrating should take care of that
>
> dg9bfc sigi
>
> Am 04.07.2021 um 20:17 schrieb Jos Stevens:
>
> Hi,
>
> When you put an attenuator on the input of the SDR, tmho
> you will not
> measure ihe input impedance of the SDR, but of the
> attenuator,  more
> or less.
>
> Jos
>
> Op 4-7-2021 om 19:43 schreef Siegfried Jackstien:
>
> ok .. the rtl dongle may be safe ... but others not
>
> maybe you can measure them when you add an attenuator
> in line (and
> calibrate WITH attenuator)
>
> how accurate that will be?? no idea ...
>
> what does the input impedance tell you??
>
> for me on sdrs most needed values are ... sensitivity
> and dynamic
> range ... but not the input impedance
>
> if you want to add filters in line ... and filter
> responce does
> change with receivers impedance ... ok then it will
> play a role
>
> greetz sigi dg9bfc
>
> Am 04.07.2021 um 19:22 schrieb Jim Lux:
>
> On 7/4/21 10:05 AM, Siegfried Jackstien wrote:
>
>
> i would never try that ... 10mw into the
> antenna socket will kill
> your sdr
>
> dg9bfc sigi
>
> perhaps not - there's protection diodes on the
> front of the RTL-SDR
> and the R820T input chip might tolerate +10dBm no
> damage
>
>
> https://www.rtl-sdr.com/wp-content/uploads/2013/04/R820T_datasheet-Non_R-20111130_unlocked1.pdf
> <https://www.rtl-sdr.com/wp-content/uploads/2013/04/R820T_datasheet-Non_R-20111130_unlocked1.pdf>
>
> doesn't give a max, but
>
>
> https://www.onesdr.com/2020/01/29/how-not-to-break-your-software-defined-radio-hardware/
> <https://www.onesdr.com/2020/01/29/how-not-to-break-your-software-defined-radio-hardware/>
>
> gives the following table (without saying where
> they got the numbers)
>
> *HackRF <https://amzn.to/3ccMZ2e
> <https://amzn.to/3ccMZ2e>>* – 5 dBm     0.3 milliwatt
> *RTL-SDR <https://amzn.to/3ies9mz
> <https://amzn.to/3ies9mz>>* +10 dBm     10 milliwatt
> *ADALM Pluto <https://amzn.to/3yQLmke
> <https://amzn.to/3yQLmke>>* +2.5 dBm 1.8 milliwatt
> BladeRF     +2.5 dBm     1.8 milliwatt
> *SDRplay RSP1A <https://amzn.to/3pqMPcZ
> <https://amzn.to/3pqMPcZ>>* 0 dBm 1 milliwatt
>
>
>
>
>
>
>
>
>
>
>
>
>
> --
> Dit e-mailbericht is gecontroleerd op virussen met Avast
> antivirussoftware.
> https://www.avast.com/antivirus <https://www.avast.com/antivirus>
>
>


--
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