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Breaking Input Stage of Spectrum Analyser with Radio TX
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Bicurico:
Hello,

This is bugging me and I don't want to break my pr cious spectrum analysers.

Imagine I have i.e. a Silent SSA3021X. It is switched off.

Could the input stage break, if I take a radio, imagine a Baofeng UV-5R and transmit with the provided antenna? Both devices are less than 1m apart and the Baofeng transmits with 5W, some models even go up to 8W.

Is this safe? Is so, is it safe because the power diminishes squared to the distance? Does it make a difference to have the SA switched off?

If this would be a problem, what if your shack is close to a DVB-T or 4G/5G transmitter? Wouldn't they transmit with considerablyore power?
radiolistener:

--- Quote from: Bicurico on November 19, 2023, 10:16:22 am ---Is this safe?

--- End quote ---

It depends on spectrum analyzer protection circuit. But in many cases transmitter can damage your device. For example several days ago my acquaintance damaged two WiFi routers and PC server just because he tested power amplifier (something like 1 kW) for short wave transmitter in the same house...

As I remember, spectrum analyzers usually have absolute maximum rating about +20..+30 dBm which is 0.1-1 W.
Baofeng UV5R has 5 W power, so it can damage it.
Bicurico:
Note that the input is not connected by cable.
What if my next door neighbour has a Baofeng and transmits 5W from the other side of the wall?

Somehow this intreagues me...
xrunner:

--- Quote from: Bicurico on November 19, 2023, 11:30:03 am ---Note that the input is not connected by cable.
What if my next door neighbour has a Baofeng and transmits 5W from the other side of the wall?

Somehow this intreagues me...

--- End quote ---

Well let's do a simple calculation and see what range we are in. Let's try these paramaters:

Tansmitter power
5W = +37 dBm

Free space calculation (simple version)

Distance = 1 m

Antenna gain of both TX and RX = 0 dBi

F = 146 MHz

Free space loss = 16 dBm
(use free space loss calculators available on internet)

So we have:

+37 - 16 = +21 dBm at input to analyzer

Many analyzers have a Max input of +20 dBm

However, your analyzer input does not have an antenna connected to it, so it won't have an antenna gain of even 0 dBi, it will be a lot lower than that. So I say no it won't harm your analyzer.

For an experiment, you would have to make a test rig shielded box with an N connector as the input with NO antenna connected, and a 50 ohm R on the inside, and be able to measure the power actually received by this passive setup a certain distance from to emitter to find out what you would get. Be an interesting test though.
Wallace Gasiewicz:
I test lots of radios, but mostly into a load. You can see something on a SA even with no connection and the SA input "open"You can put an few wraps of wire on the outside of a transmitting coax and get a signal into your SA for spectrum analysis.
I have not damaged anything yet.If you are concerned put a 50 ohm load on the input of your test equipment to protect it. The load does not have to be good quality, so cheap ones can serve this purpose and provide a dust cover for the BNC. (or whatever)
We did analyze a Baofeng with an antenna connected to a SA and analyzed the Baofeng 2 meter spectrum emissions.  Several results with several transmitters showed spurious emissions that are way above FCC specifications..We did not damage the SA.
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