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0dBm and -60dBm calibration

Hans Summers
 

Hi all

Possibly interesting for people with an Antuino who want to check the calibration; or many other pieces of test equipment - I built an interesting 7MHz signal generator with very accurate 0dBm and -60dBm reference outputs yesterday. I made a YouTube video about it see https://youtu.be/732ESoul088

73 Hans G0UPL

 

Hans,

AFAIK the Antuino reads from -20dbm to -100dbm at the input. The IF amp amps the signal
by 30db making the -20dbm at input into +10dbm at the AD8307. The sketch takes care
of the maths. Any higher level than -20 needs external attenuator (probably internal in
the next version?).

Raj


At 12/09/2019, you wrote:
Hi all

Possibly interesting for people with an Antuino who want to check the calibration; or many other pieces of test equipment - I built an interesting 7MHz signal generator with very accurate 0dBm and -60dBm reference outputs yesterday. I made a YouTube video about it see https://youtu.be/732ESoul088

73 Hans G0UPL
http://qrp-labs.com

Hans Summers
 


Hi Raj

> AFAIK the Antuino reads from -20dbm to -100dbm at the input. The IF amp amps 
> the signal by 30db making the -20dbm at input into +10dbm at the AD8307. The
> sketch takes care of the maths. Any higher level than -20 needs external 
> attenuator (probably internal in the next version?).

Question is - if the Antuino (or any other piece of test equipment) says -34dBm (for example) on its screen... how do you know the accuracy of that? 

This calibration generator generates both 0dBm and -60dBm signals so the latter would be suitable for Antuino testing. 

I do have a Dayton Antuino so could try it. But I am waiting on the upgrade components pack... 

73 Hans G0UPL

 

What I am saying here Hans is that 0dbm is no use to check an Antuino unless
we have a 20db attenuator.

Calibrator will be useful for the Antuino between -20 and -80

Just like you are using a clock osc for signal reference, Antuino used the internal
osc level for calibration. Its pretty accurate, worst case is 2db error but mostly
1db. We can do better with AD8310 which is 0.5db with 20mv/dbm compared to
AD8307 which is 1db error and 25mv/dbm. That mod will need sketch correction.
Waiting to try that once I get back to town.

Initially drove me nuts so I call it Mentuino!

Raj


At 13/09/2019, you wrote:

Hi Raj

> AFAIK the Antuino reads from -20dbm to -100dbm at the input. The IF amp ampsÂ
> the signal by 30db making the -20dbm at input into +10dbm at the AD8307. The
> sketch takes care of the maths. Any higher level than -20 needs externalÂ
> attenuator (probably internal in the next version?).

Question is - if the Antuino (or any other piece of test equipment) says -34dBm (for example) on its screen... how do you know the accuracy of that?Â

This calibration generator generates both 0dBm and -60dBm signals so the latter would be suitable for Antuino testing.Â

I do have a Dayton Antuino so could try it. But I am waiting on the upgrade components pack...Â

73 Hans G0UPL
http://qrp-labs.com

Hans Summers
 

Hi Raj

> What I am saying here Hans is that 0dbm is no use to check an Antuino 
> unless we have a 20db attenuator.
> Calibrator will be useful for the Antuino between -20 and -80

Yes, I understand that... but please watch my video https://youtu.be/732ESoul088 or look at the web page that inspired it (http://dl6gl.de/schlagworte/rf-calibration-generator) ... the calibrator already HAS a 60dB attenuator in it. 

What I am saying is that it provides BOTH a 0dBm output AND a -60dBm output. Therefore the -60dBm output is eminently suitable for checking the calibration of an Antuino. 

I was so surprised that the thing works so well... the reading on my spectrum analyzer was 0dBm +/- 0.05dBm and the 'scope 0dB +/- 0.1dBm... it is improbable that the calibrator, spectrum analyzer and 'scope could all agree so precisely by chance alone... so it led to me regaining the impaired trust in these instruments, and thankfully having a method to check calibration in future too. 

73 Hans G0UPL
http://qrp-labs.com

Jonas Sanamon
 

Wow, that's impressive!

It reminds me of when I first got my Gepetto GPSO a couple of years ago, and thought I should calibrate my HP 8924c Service monitor. Turned out that 20+ year old instrument that hadn't been calibrated in years was off in frequency by just fractions of a Hz :-)

Cheers,
Jonas - SM4VEY

Den fre 13 sep. 2019 kl 20:11 skrev Hans Summers <hans.summers@...>:


I was so surprised that the thing works so well... the reading on my spectrum analyzer was 0dBm +/- 0.05dBm and the 'scope 0dB +/- 0.1dBm... it is improbable that the calibrator, spectrum analyzer and 'scope could all agree so precisely by chance alone... so it led to me regaining the impaired trust in these instruments, and thankfully having a method to check calibration in future too. 

73 Hans G0UPL
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