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Noise Sources

 

I recently purchased noise source from an eBay vendor in China for the purpose of making filter measurements with my TinySA or TinySA Ultra. The specification on the case of the noise source indicates a range of 0.001-3000 MHz. I have completed some preliminary measurements using my TinySA Ultra and it appears that the power output over most of the 0 to 800 MHz range is approximately -40 dBm except at the lower frequencies in the range where it jumps up to perhaps +20 dBm. I suspected that the output of the noise source contained a DC component but I measured 0 volts DC with my DMM. If I divide the spectrum into three channels, most of the power is contained in the lower third of the range as one might suspect.

If I place an external 30 dB attenuator in the RF path and manually set the internal attenuator to 0 dB, the power output at the low end of the noise spectrum does not exceed 0 dBm. Will this allow me to make the filter response measurements that I intended to make?

Any comments or advice would be appreciated!

Thanks,

Ed, K0KC
?
k0kc@...
http://k0kc.us/
 

De
For a noise source it's not important what the noise level at any frequency is put the total power it outputs going into the tinySA
There is a simple procedure to check if you are safe
Connect the noise source to the tinySA using an extra 30dB attenuator
Activate MEASURE/CHANNEL POWER and enter the central frequency of tinySA, 400MHz for the Ultra, and for the channel width use one third of the total span, say 260MHz
Now you will see the screen divided in 3 and at the top the total power power in each of the 3 parts
Probably the leftmost number will be the largest.
As long as each number is below -40 there is little risk in damaging the tinySA when using the noise source without the extra 30dB attenuator.

--
For more info on the tinySA go to https://tinysa.org/wiki/
 

Ok, Eric, I think that the noise source is not my problem. When I divide the spectrum into three channels centered at 400 MHz and a channel width of 266 MHz and do not connect the noise source, I see -3.3 dBm in the left channel, -65 dBm in the center channel and -65 dBm in the right channel. Connecting the noise source does not make much difference since the power is so strong in the left channel. Is this behavior a problem with my TinySA Ultra?

I just checked this with my TinySA and the same issue exists with center frequency of 175 MHz and a span of 117 MHz.
--
Ed, K0KC
?
k0kc@...
http://k0kc.us/
 

FYI, the TinySa and the TinaSA Ultra are running the latest firmware release.
--
Ed, K0KC
?
k0kc@...
http://k0kc.us/
 

At what frequency are the filters configured for that you wish to measure??

Connect the noise source through a 3 to 6 dB attenuator rated for this frequency range between the noise source and the input of either TinySA.? This is to assure at or below a 2:1 SWR from either end.? Do a max hold over several passes of this frequency range.? Now you have a good idea of the flatness of the noise source, assuming the TinySA is flat from 1 through 1000 MHz (or your chosen frequency range).? You can confirm the flattness of the TinySA by using your HP sig gen - assuming it's flat over the specified range of frequencies.

Dave - W?LEV ??
.?

On Tue, Dec 20, 2022 at 9:22 PM Ed Wilson via <ed.wilson=[email protected]> wrote:
Ok, Eric, I think that the noise source is not my problem. When I divide the spectrum into three channels centered at 400 MHz and a channel width of 266 MHz and do not connect the noise source, I see -3.3 dBm in the left channel, -65 dBm in the center channel and -65 dBm in the right channel. Connecting the noise source does not make much difference since the power is so strong in the left channel. Is this behavior a problem with my TinySA Ultra?

I just checked this with my TinySA and the same issue exists with center frequency of 175 MHz and a span of 117 MHz.
--
Ed, K0KC
?



--
Dave - W?LEV
 

Thanks for your response, Dave!

I wrote you a longer response but I somehow must have deleted it before it was sent. In any case, I will be using the TinySA and/or TinySA Ultra to help me in the design of a wide range of filters.

I checked your QRZ.com page and am impressed with the scenic QTH!
--
Ed, K0KC
?
k0kc@...
http://k0kc.us/
 

There is a story on the location, but too long for an email.? In short, we lost everything in a major forest fire in 2012 when we lived in the foothills of the Rockies.? It took some major effort to find this property which was in the bank at the time. We rebuilt here.? All the major windows on the house have that view.? I should mention that my other hobby is radio astronomy, so that drove locating this QTH.

Dave - W?LEV


On Tue, Dec 20, 2022 at 10:08 PM Ed Wilson via <ed.wilson=[email protected]> wrote:
Thanks for your response, Dave!

I wrote you a longer response but I somehow must have deleted it before it was sent. In any case, I will be using the TinySA and/or TinySA Ultra to help me in the design of a wide range of filters.

I checked your QRZ.com page and am impressed with the scenic QTH!
--
Ed, K0KC
?



--
Dave - W?LEV
 

On Tue, Dec 20, 2022 at 01:22 PM, Ed Wilson wrote:
Ok, Eric, I think that the noise source is not my problem. When I divide the spectrum into three channels centered at 400 MHz and a channel width of 266 MHz and do not connect the noise source, I see -3.3 dBm in the left channel, -65 dBm in the center channel and -65 dBm in the right channel. Connecting the noise source does not make much difference since the power is so strong in the left channel. Is this behavior a problem with my TinySA Ultra?
Ed,

You do not have a problem with your tinySA Ultra.? Erik had suggested that you use a span of 260 Mhz and you used 266 MHz. and this causes an issue with the Channel Power measurement.? Here are a few screenshots.

400 MHz. centre 260 MHz. span (Erik's suggestion)




400 MHz. centre 263 MHz. span




400 MHz. centre 266 MHz. span? (your measurement)




So why do we see this at 266 MHz. span?? The reason is that the noise floor of the tinySA increases considerably below a few MHz. (see screenshot below)? and a span of 266 MHz. starts making measurements at 1 MHz.? The channel power measurement assumes a flat response so measurements have to start a few MHz. up. in order to work.? A span of 260 or 263 works OK for this measurement.




Roger
 

Roger,

Thanks for the info...seems to be working fine. This is my first experience working with a wideband noise source and I purchased it just for the educational value.
--
Ed, K0KC
?
k0kc@...
http://k0kc.us/
 

Attached, please find the response curve for a low pass filter generated by my TinySA Ultra and my new noise source. The curve was generated using TinySA-App.

Thanks again to all who helped me understand how to properly use the noise source with the TinySA Ultra!

Ed, K0KC

k0kc@...

http://k0kc.us/

--
Ed, K0KC
?
k0kc@...
http://k0kc.us/

Low Pass Filter.jpg

 

Just blows my mind what we can do with just a couple hundred dollars. I'm 75 and remember in college lab manually measuring hundreds of points and plotting on graph paper with equipment you could only dream of using let alone own! Something like the TinySa would have been pie in the sky science fiction! ?


On Wed, Dec 21, 2022, 11:06 AM Ed Wilson via <ed.wilson=[email protected]> wrote:
Attached, please find the response curve for a low pass filter generated by my TinySA Ultra and my new noise source. The curve was generated using TinySA-App.

Thanks again to all who helped me understand how to properly use the noise source with the TinySA Ultra!

Ed, K0KC



--
Ed, K0KC
?
 

We are at the point where colleges and universities could require engineering students enrolled in a related course to purchase a TinySA, just like a textbook.

I may be old, but I do remember the days when textbooks were printed on paper and purchased in a bookstore rather than as PDF files!
--
Ed, K0KC
?
k0kc@...
http://k0kc.us/
 

On Wed, Dec 21, 2022 at 12:40 PM, Ed Wilson wrote:
when textbooks were printed on paper and purchased in a bookstore
As do I! ?Not only that, I could afford the textbooks.

larry

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