If I measure an amplifier, 0dBm may be a lot.

add a 20 or 30 db inline.. calibrate with att .. then measure

if you want to measure a power amp then maybe much more att needed

but say you want to measure a predriver or a low noise receving preamp
then 20 db should do the job well

can be split in 2x 10 db (depends on what level you want at the amps
input) ...

hth

dg9bfc sigi

ps i even could measure my 50 db 2.4 ghz poweramp (25w peak)... with 60
db inline

Am 13.03.2023 um 21:12 schrieb Leif M:

> If I measure an amplifier, 0dBm may be a lot.
>

Remember that the NanoVNA V2 Plus 4 output is a square wave, not a sign
wave, so it's rich in harmonics. You may want to watch Joe Smith's video
on some problems when measuring amplifiers with the nanoVNA series.

On Tue, Mar 14, 2023 at 9:59 AM Siegfried Jackstien <
siegfried.jackstien@freenet.de> wrote:

> add a 20 or 30 db inline.. calibrate with att .. then measure
>
> if you want to measure a power amp then maybe much more att needed
>
> but say you want to measure a predriver or a low noise receving preamp
> then 20 db should do the job well
>
> can be split in 2x 10 db (depends on what level you want at the amps
> input) ...
>
> hth
>
> dg9bfc sigi
>
> ps i even could measure my 50 db 2.4 ghz poweramp (25w peak)... with 60 db
> inline
> Am 13.03.2023 um 21:12 schrieb Leif M:
>
> If I measure an amplifier, 0dBm may be a lot.
>
>
>
>

For these kind of worries we designed the RF Power Snitch.

If I put a 20dB attenuator between VNA and amplifier, and calibrate with it, does the VNA show input impedance too? Yes, It would be nice to able to adjust output power in VNA.

I need alot of lowpass filters. Not fun.

put the att behind the amp .. then vna measures direct yor impedance on
input of amp

dg9bfc sigi

Am 15.03.2023 um 10:10 schrieb Leif M:

> If I put a 20dB attenuator between VNA and amplifier, and calibrate
> with it, does the VNA show input impedance too? Yes, It would be nice
> to able to adjust output power in VNA.
>
> I need alot of lowpass filters. Not fun.
>

Yes but input impedance maybe different at 1mW than with much lower power. It looks like measuring some amplifiers requires compromises or several steps.

On 3/15/23 2:10 AM, Leif M wrote:
> If I put a 20dB attenuator between VNA and amplifier, and calibrate with
> it, does the VNA show input impedance too? Yes, It would be nice to able
> to adjust output power in VNA.
>

Yes, but the uncertainty of the measurement is greater, because the
reflected signal is 40dB lower (20dB going out, 20 dB coming back), so
at some point you're up against the basic SNR of the instrument.

And you can't necessarily put the pad on the output, because 0dBm might
be enough to damage the input on a sensitive LNA.

Adjustable output power is what you get with a more expensive VNA
(smile) - you can attenuate before the bridge/directional coupler. so
you don't take the 20dB coming back hit.

FWIW same sort of thing applies on the other port.

and will also maybe change with bias

yes .. measure (and tune) an amp can be tricky

dg9bfc sigi

Am 15.03.2023 um 22:35 schrieb Leif M:

> Yes but input impedance maybe different at 1mW than with much lower
> power. It looks like measuring some amplifiers requires compromises or
> several steps.
>

if you know how to solve it you maybe can use a set off attenuators and
additional amplifiers to expand the measure area of a cheaper lna like
the vna v2 ... but getting close to a prefessional device with a few
percent of the cost is not an easy task (as we all know professional
gear cost an arm and a leg)

a few things can be solved with software satsagen and a pluto cause ther
YOU CAN set the power of the tx part and the sensitivity (gain) of the
rx part (remember not to cook the input ... again attenuators are your
friends here)

i did not need att at the tx end but i needed 60 db on the output of the
amp towards the rx end of the pluto

(sorry that is a bit off topic)

dg9bfc sigi

Am 16.03.2023 um 01:39 schrieb Jim Lux:

> On 3/15/23 2:10 AM, Leif M wrote:
>> If I put a 20dB attenuator between VNA and amplifier, and calibrate
>> with it, does the VNA show input impedance too? Yes, It would be nice
>> to able to adjust output power in VNA.
>>
>
> Yes, but the uncertainty of the measurement is greater, because the
> reflected signal is 40dB lower (20dB going out, 20 dB coming back), so
> at some point you're up against the basic SNR of the instrument.
>
> And you can't necessarily put the pad on the output, because 0dBm
> might be enough to damage the input on a sensitive LNA.
>
> Adjustable output power is what you get with a more expensive VNA
> (smile) - you can attenuate before the bridge/directional coupler. so
> you don't take the 20dB coming back hit.
>
> FWIW same sort of thing applies on the other port.
>
>
>
>
>
>

On Thu, Mar 16, 2023 at 04:20 AM, Jim Lux wrote:

>
> And you can't necessarily put the pad on the output, because 0dBm might be
> enough to damage the input on a sensitive LNA.

I think I have my words unclearly. I meant the left connnector of the V2 Plus4 =output ?. That is an attenuator between output of the VNA and input of the amplifier. I have read in these forums, that an other attenuator is recommended at amplifier output, (and before input of the VNA)

On 3/16/23 11:43 AM, Leif M wrote:
> On Thu, Mar 16, 2023 at 04:20 AM, Jim Lux wrote:
>
> And you can't necessarily put the pad on the output, because 0dBm
> might be enough to damage the input on a sensitive LNA.
>
> I think I have my words unclearly. I meant the left connnector of the V2
> Plus4 =output ?. That is an attenuator between output of the VNA and
> input of the amplifier. I have read in these forums, that an other
> attenuator is recommended at amplifier output, (and before input of the
> VNA)

One can put an attenuator on both ports - it makes the measurement
uncertainty greater (lower SNR) but it woks.

Attenuator on amplifier input (Tx side of VnA) keeps from damaging a
sensitive amplifier input).
Attenuator on output (Rx side of VNA) keeps from damaging the VNA