Electronics > Beginners
How to **Safely** and properly align a Transmitter with a spectrum analyzer
The_Spectrum.A_idiot:
Dear fourfathom
thank you very much for the contribution and the idea
--- Quote from: fourfathom on August 14, 2019, 01:25:02 am ---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.
--- End quote ---
hopefully soon I may try to make this so called (RF sampler lets call it ? ) although I would use N type all over for my convince although the response in my application is a bit more critical to go up to 500 mhz
anyhow when I will get more experience into making my own RF circuits I will try to do this ( seems very easy and a simple design with almost nothing could go wrong )
thank you for your time and effort and reply to my question
The_Spectrum.A_idiot
The_Spectrum.A_idiot:
Dear tautech
Thank you so very much for the links , I skimmed though most of them before buying the instrument although now it looks like I need to read it more and more thoroughly to get a better grasp of understanding my instrument
--- Quote from: tautech on August 14, 2019, 02:08:12 am ---
--- 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.
--- End quote ---
now I will most probably buy a more reputable 50db attenuator and call it a day or maybe even an RF sampler ,
anyway it looks like I have my work cut out for me so I should get to reading :D Thank you again for pointing out the details i've missed and for the links too ,
Thank you in advance
The_Spectrum.A_idiot
The_Spectrum.A_idiot:
Dear vk6zgo
Thank you for your time and response to point out several things I didn't even thought about ,
--- Quote from: vk6zgo on August 14, 2019, 03:15:41 am ---
--- Quote from: radiolistener on August 13, 2019, 10:53:15 pm ---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.
--- End quote ---
I dunno about Chinese stuff, but the normal convention with smaller attenuators is that the input to the attenuator is a female "N" connector, & the output a captive male "N", to make it easier to connect directly to a following test instrument.
Although the one linked to is getting a bit close to the size where it could damage the SA's input front panel connectors due to its mass & mechanical advantage, I'm pretty certain it would follow that convention.
Similar units from the USA, the UK, Japan, & Germany commonly have an arrow silkscreened onto the body, showing the signal path through the device, as do many of the large "thruline loads".
Higher power "thrulines" & the like, often have female "N" connectors on both ends--- maybe to stop morons hanging them off the front of SAs, but more probably, so they don't need to use an adaptor to connect to a standard cable.
At 2 watts it is doubtful that it would make much difference if the OP got the attenuator input & output mixed up.
--- End quote ---
The direction of the attenuator ( yes indeed there are no markings , and indeed that is the most typical way i looked on more expensive attenuators on the web that the male part is to the instrument and female part to the transmitter )
regarding the mechanical advantage once I plugged it on the SA I didn't think about it but now I am definitely buying a barrel connector and having a small patch cable for it
thank you in advance for your time and ideas :D
The_Spectrum.A_idiot
The_Spectrum.A_idiot:
Dear 0culus
Thank you very much for the youtube video amazing channel definitely going to watch all his videos :D
--- Quote from: 0culus on August 14, 2019, 03:19:46 am ---Also a quality directional coupler or RF sampling tee can be helpful. See:
--- End quote ---
Damn that capacitive sampler looks amazing ( definitely making one out of copper pipe as the person on the video suggested)
thank you so very much
The_Spectrum.A_idiot
0culus:
Alan is a forum member too; FWIW.
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