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Hi all,

What output voltage should I expect from the NanoVNA into a 50 ohm load with CW FREQ selected under the STIMULUS menu.

73
John
M0JBA

-10dBm

Thanks Erik,

I’m in the right ballpark.

73
John
M0JBA

John,
From the specs below, expect -13 to -9 dBm. Since you are a ham, the power to voltage calculation should be trivial to you.

Basic Parameters:
- PCB: 54mm x 85.5mm x 11mm (without the size of connectors, switches)
- Measurement Frequency: 50KHz ~ 300MHz (50KHz -900MHz, enable extended firmware)
- RF Output: -13dbm (maximum -9dbm)
- Frequency Accuracy: ???0.5ppm
- Measurement Range: 70dB (50kHz-300MHz), 50dB (300M-600MHz), 40dB (600M-900MHz) enable extended firmware)
- Port SWR: < 1.1
- Display: 2.8 inch TFT (320 x240)
- USB Interface: USB Type-C; Communications Mode: CDC (Serial)
- Power Supply: USB 5V 120mA, built-in 400mAh electricity, maximum charging current 0.8A
- Number of Calibration Points: 101 (Fixed)
- Number of Scanning Points: 101 (Fixed)
- Display Tracking: 4, Marking: 4, Save Setting : 5
- Measuring S parameters, voltage standing wave ratio, phase, delay, Smith chart and the like

Checking with my ‘scope, at 7MHz I get 0.2V pk-pk which is -10dBm.

Passed through a 40m lpf it is still 0.2V pk-pk but the scope trace looks a lot nicer!

Thanks for the help.

73
John
M0JBA

Nice to see the output verification with an oscilloscope. I guess in theory, with a completely different firmware it could be re-purposed as an extremely low power WSPR mode transmitter (0.1 mW)....but the catch being that an external clock of some kind would be needed to keep the proper transmission cadence. In the past I've had some success running WSPR mode at 0.1 mW power output. But I digress...what an amazing thing the nanoVNA is.

On Wed, 18 Sep 2019 at 16:39, John Baines via Groups.Io <jbaines=
[email protected]> wrote:

Checking with my ‘scope, at 7MHz I get 0.2V pk-pk which is -10dBm.

Passed through a 40m lpf it is still 0.2V pk-pk but the scope trace looks
a lot nicer!

Thanks for the help.

The filter will obviously chop off the harmonics,

The high-end VNAs, like the Keysight PNA-X, have the harmonics suppressed
by 60 dB or so. Obviously, they work a very different way to the NanoVNA,
but one could buy 10,000 NanoVNAs for the cost of even a modestly equipped
PNA-X,

73
John
M0JBA

On 18 Sep 2019, at 16:21, John Baines via Groups.Io <jbaines=

[email protected]> wrote:

Thanks Erik,

I’m in the right ballpark.

73
John
M0JBA

On 18 Sep 2019, at 16:19, erik@... wrote:

-10dBm

--
Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
Essex, CM3 6DT, United Kingdom.
Registered in England and Wales as company number 08914892

Tel 01621-680100 / +44 1621-680100

I think the -10 dBm number is based on conversion of the unterminated voltage. My unit puts out -17 dBm at 100 MHz and -19 dBm at 900 MHz when properly terminated in a 50 ohm load. This level is consistent with other Si5351 devices I own.

One of those devices is the RFzero board which is a GPS referenced, Arduino based synthesizer. It comes with some very nice beacon software that allows it to run WSPR up to 1.5 GHz using harmonics of the Si5351. I have mine operating on 23 cm and get good WSPR decodes using the fifth harmonic.

Warren Allgyer
WA8TOD

I just measure 100mv peak into 50R at 50Khz to 50Mhz (-10dbm)
At 70Mhz it was 70mv (convenient to remember).
I was amazed at how accurate the out put frequency was according to my GPS calibrated freq counter too.

73 de Andy

Hi, Andy,

we had the same idea, I measured the output and the frequency accuracy on the weekend. It is very bad if there are 5 kHz difference, e.g. on LF...the band is < 2kHz wide.
I have set the measurement results under Photos, Output to frequency.

Measuring equipment Advantest R3131 with Rubidium-10MHz reference.

73 Joe

The output power of the SI5351 is automatic set depending the requested sweep frequency, 2mA below 300MHz, 8mA above 300MHz
Similar for a manually set fixed output frequency using the freq command

You can manually control the power through console by issuing

power [0-3]

The power is in small steps controlling the SI5351 current into the output attenuator
0->2mA
1->4mA
2->6mA
3->8mA

Issuing
power -1
sets the nanoVNA again in automatic power mode

If you report output power please indicate at which power setting the output is generated.

Some clarification from my earlier measurement.

The Measurement output from CH0 ranges from -13 dBm at 55 kHz to -36 dBm at 900 MHz..... a more than 23 dB variance.

Beginning at the first increment above 300 MHz the Measurement output switches from fundamental to 3rd harmonic. So, for example, when measuring at 330 MHz the 330 MHz Measurement output being used will be at -19 dBm the there will also be a much higher power fundamental signal output at 110 MHz at -9 dBm. The Nanovna ignores this fundamental frequency by virtue of its heterodyne mixing but users should be aware of its presence when performing S21 measurements of preamps and the like. These relatively high power fundamental frequencies can easily overload amplifiers and distort measurement results.

Another example: The Measurement output at 900 MHz is way down at -36 dBm but the 300 MHz fundamental that is generating that measurement frequency is also present at a whopping -9 dBm, nearly 30 dB higher! User beware!

Warren Allgyer

Here is my measurements:

50 Ohm load, sweep 50k-900M:
Peak voltage: 182 mVpp
RMS voltage: 92 mVrms
So, the max power level about -7.7 dBm

1 MOhm 18pF load, sweep 50k-900M:
Peak voltage: 324 mVpp
RMS voltage: 165.3 mVrms
So, the max power level about -45 dBm (note, 1 Mohm load!)

According to these values, the output impedance of CH0 is about 39 Ohm.

Measured with 100 MHz bandwidth scope, so the real voltage may be a little higher.

This is the output from my NanoVNA as measured on an HP 8568B spectrum analyzer in Max Hold mode (50 Ohm input impedance). See attached photos.

~10 MHz -13 dBm
~100 MHz -9 dBm
~300 MHz -9.60 dBm
~600 MHz -20.6 dBm
~900 MHz -23.2 dBm

Therefore, there is an approximately 10 to 13 dBm drop in output level going above 300 MHz which is understandable due to the higher frequencies being derived from harmonics. What I am puzzled by is why the output is low (in the -13 dBm range) for frequencies below 100 MHz?

It makes a lot of sense.
From 0-300MHz you get the 2mA drive fundamental and its harmonics
From 300-900MHz you get8mA drive with fundamentals from 100-300MHz and its harmonics from 300-900MHz
So between 100-300MHz you see the fundamental of the 300-900MHz 3rd harmonic output.
To verify this you should do separate measurements for 0-300MHz and 300-900MHz