Products > Test Equipment

Breaking Input Stage of Spectrum Analyser with Radio TX

<< < (4/6) > >>

joeqsmith:

--- Quote from: xrunner on November 22, 2023, 02:51:54 am ---
--- Quote from: Bicurico on November 21, 2023, 06:58:20 pm ---Another question: what is the difference in using i.e. three 10dB attenuators in series or a load with a big cooler?

--- End quote ---
...
Well then you have 100 mW of power that needs to see a 50 ohm load (or the proper impedance you are working with). You can't just leave the output open because three 10 dB attenuators in series is a 30 dB attenuator - not a dummy load.

--- End quote ---

Guessing even two series 10dB attenuators, unterminated is would be fine in most cases.  Return loss would be 40dB which is pretty decent.   

***
Just for a quick comparison,  I used the LiteVNA to sweep from 1.5 - 500MHz.  Performed a SOLT using the ideal model and my sorted mini-circuits load.    Measured the return loss of the load supplied with the LiteVNA (black).   Replaced the load with a 10dB Midwest Microwave attenuator that was left unterminated (brown).  Measured roughly 22dB.   Added a second 10dB attenuator in series and left it them unterminated.  Return loss is now comparable with the load.

Bicurico:
So, I finally got some short break to test it myself.

First test was with my cheapest device, the TinySA:



I tested outside, far enough from my other more valuable devices, but there was no problem at all.

I even dared to attach an antenna do the TinySA.

Feeling comfortable, I repeated the test inside, on my Rohde&Schwarz CMU200:



Again, no issues, I removed the attenuator and termination and still got a marginal signal.

This cleared my mind, it is safe to play with my radios next to the spectrum analysers, as long as they don't have a matching antenna.

Thank you all for your inputs.

Kind regards,
Vitor

Wallace Gasiewicz:
You said you had 75 ohm Terminators, if these are just Loads you can check the performance of your VNA quickly by using a 75 ohm load on the 50 ohm output.   
 The resulting VSWR should be 1.5 to 1. Of course lots of cheap loads do not handle high frequency well. But a "quick check" none the less.

pdenisowski:
I have an amateur radio station which I regularly operate with 100W on HF and up to 100W on VHF.  I also have numerous high end spectrum analyzers, network analyzers, etc. located < 10 meters from the antennas.  I am completely unconcerned with damaging my instruments and have never had any instruments damaged by OTA signals.

And although I can't go into any details in a public forum, I have often used some of our (R&S) spec ans to measure over-the-signals from very high power transmitters in very close proximity and have never seen an instrument damaged by this.  (Overloaded, yes, but not physically damaged)

As some other folks have mentioned, you can use the free space path loss equation to estimate the power at the spec an input if you're concerned.

That said, I have seen plenty of people blow out the front end of an analyzer by directly connecting (with a cable) something they shouldn't have been directly connecting without a sufficiently large pad :)

CatalinaWOW:
The first attenuator in the string does not dissipate 100W. If it did there would be no power transmitted to the next stage.  A nit since it does dissipate 90W.   This does not require a chiller, but may benefit from a good finned heat sink.  It would otherwise heat to temperatures comparable to a 100W incandescent bulb and could burn your skin.   Obviously the first attenuator must be rated for greater than 90 watts which will likely mean it has the aforementioned fins.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod