Electronics > Beginners
How to **Safely** and properly align a Transmitter with a spectrum analyzer
The_Spectrum.A_idiot:
Dear All ,
I would like to thank everyone in advance that will answer my question/s and for their time ,
So I have a Spectrum analyzer a "Siglent SSA3021X"
so I learned how to tune filters by doing and failing and doing some light reading , and finally succeeding
although I know that the front end of Spectrums are very sensitive into input power ,
so as per recommendation of a friend I bought this :"100W N Attenuator 50db male to female DC-3GHZ 50ohm RF"
https://www.ebay.com/itm/100W-N-Attenuator-50db-male-to-female-DC-3GHZ-50ohm-RF/272899586791
Although still I am very skeptical if I can plug a transmitter at its lowest power output at 2W with this attenuator in line and still be safe from the maximum power input the Spectrum can handle ,
Is there any other way ( mathematically to be able to calculate if I fall within the maximum acceptable range of my analyser and how to do this safely and properly )
I was thinking to get a signal sampler although they are too expensive and almost nowhere to be found in a price range around 100$ 200$ max
So the question is how is the most proper and safe way to align and check a transmitter (health) and generally see the bandwidth etc
If this question was answered elsewhere I am sorry in advance
thank you in advance
The_Spectrum.A_idiot
radiolistener:
yes, you can connect it.
2 W = 33 dBm, after 50 dB attenuator it will be 33 - 50 = -17 dBm, it should be safe for spectrum analyzer.
Before connect I suggest you to check if your attenuator works properly.
And note! These Chinese attenuators have just one side which is intended to apply high power. If you connect transmitter to the wrong side, your attenuator will burn out.
This is not trivial to understand which side is intended for high power. I found that Chinese manufacturers probably marking it with a small "SU" marking on connector, but this is not 100% information, just my finding. I burned out several attenuators in such way, because these attenuators don't have any instruction or manual or any kind of note about where is input and where is output and there is even no any mention that they are single way. And the worse thing is that sellers also don't know it ;D So it's just your luck to find where is proper input ;D
I think that your attenuator probably has high power input on the bottom connector (see first photo on the product description). Check if it has "SU" mark. If it is present, then this connector probably high power. But I cannot guarantee... :D
May be someone can suggest more reliable way to check which connector is intended for high power input.
hfleming:
Another trick that we used used years ago to protect spectrum analyzers, is to use a «protection box» at the input of the analyzer. All it was was a 375mA fast acting picofuse in line with the RF input. (In series with the fuse, you can also add a 100nF 1kV cap just to make sure no DC can get in, as well as a high value resistor to GND to drain static, if you forget to disconnect you analyzer from your external antnnana). You can also use a PIN-diode limiter, that you can get on e-Bay. (Frequency respons might roll off, but you can easily compensate for it).
But in anycase, a 50dB pad will definitely be good enough, even if you forget to switch your radio to 2W. (I assume you don’t have a 1kW transmitter).
fourfathom:
I bought a 50dB power attenuator (Chinese), and measured the actual attenuation at 39dB. It was reasonably flat from DC to 1 GHz, so I just put a "39dB" label on it and still use it. I sometimes use it for testing my ham transmitters.
Another test device I have is a -40dB tap. This has two BNC connectors with a direct "through" connection: one goes to the device under test, and the other to a dummy load (a cheap 100W unit). The third port is a SMA jack, with a 40dB "L-pad" attenuator, using a few low-power resistors. My simple construction gave me a flat response out beyond 100MHz.
tautech:
--- Quote from: The_Spectrum.A_idiot on August 13, 2019, 10:29:33 pm ---Dear All ,
I would like to thank everyone in advance that will answer my question/s and for their time ,
So I have a Spectrum analyzer a "Siglent SSA3021X"
so I learned how to tune filters by doing and failing and doing some light reading , and finally succeeding
although I know that the front end of Spectrums are very sensitive into input power ,
so as per recommendation of a friend I bought this :"100W N Attenuator 50db male to female DC-3GHZ 50ohm RF"
https://www.ebay.com/itm/100W-N-Attenuator-50db-male-to-female-DC-3GHZ-50ohm-RF/272899586791
Although still I am very skeptical if I can plug a transmitter at its lowest power output at 2W with this attenuator in line and still be safe from the maximum power input the Spectrum can handle ,
Is there any other way ( mathematically to be able to calculate if I fall within the maximum acceptable range of my analyser and how to do this safely and properly )
I was thinking to get a signal sampler although they are too expensive and almost nowhere to be found in a price range around 100$ 200$ max
So the question is how is the most proper and safe way to align and check a transmitter (health) and generally see the bandwidth etc
--- End quote ---
Welcome to the forum.
The datasheet on P5/9 sets out the maximum input parameters under Amplitude and Level:
https://www.siglenteu.com/wp-content/uploads/dlm_uploads/2017/10/SSA3000X_DataSheet_DS0703X-E04A.pdf
Of important note: Maximum average RF power 30 dBm, 3 minutes, fc≥10 MHz, attenuation >20 dBm, preamp off
Further in the Users manual in 2.1.3 Amplitude (P38-41/95) in 2.1.3.4 Units are the amplitude conversion relationship formulas.
https://www.siglenteu.com/download/7918/
There is 51dB of user input attenuation available but best practice with strong signals is to use external attenuation to get signals to low levels.
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