Electronics > Beginners

How to **Safely** and properly align a Transmitter with a spectrum analyzer

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David Hess:
A directional coupler between the amplifier and load is safer than a big attenuator and they are more common than samplers and often more rugged.

fourfathom:

--- Quote from: David Hess on August 14, 2019, 08:04:38 pm ---A directional coupler between the amplifier and load is safer than a big attenuator and they are more common than samplers and often more rugged.

--- End quote ---

Safer in what way?  A directional coupler still has to have an appropriate coupling ratio (or additional attenuators), and the frequency range is generally much narrower than a resistive attenuator.  I use directional couplers, but I do wonder about your "safer" comment.

David Hess:

--- Quote from: fourfathom on August 14, 2019, 08:19:02 pm ---
--- Quote from: David Hess on August 14, 2019, 08:04:38 pm ---A directional coupler between the amplifier and load is safer than a big attenuator and they are more common than samplers and often more rugged.
--- End quote ---

Safer in what way?  A directional coupler still has to have an appropriate coupling ratio (or additional attenuators), and the frequency range is generally much narrower than a resistive attenuator.  I use directional couplers, but I do wonder about your "safer" comment.
--- End quote ---

A directional coupler does not have to dissipate the power so there are fewer issues with overheating.  This makes power attenuators and terminators less rugged or at least easier to misuse.  Samplers have the same advantage but are not as common as directional couplers.

Directional couplers and samplers can still of course fail catastrophically.

The_Spectrum.A_idiot:
Dear radiolistener

thank you so very much for the help yes indeed after having the onboard attenuator at 50 DB and the external one and transmitting 2 W i get a very small signal well with in the range of the front end of the Spectrum ,

Thank you for your time


--- 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.

--- End quote ---
This was very nice to know how to calculate everything


--- Quote from: radiolistener on August 13, 2019, 10:53:15 pm ---Before connect I suggest you to check if your attenuator works properly.


I did by using the onboard Tracking Gen ( i presumed is safe since it is on the instrument anyway )



--- Quote from: radiolistener on August 13, 2019, 10:53:15 pm ---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 ---

--- End quote ---
No such marking was found
Although a friend with more experience told me that there are no such "sides" per say lastly no 'SU' mark exists I used it the way I found convenient the N type male on the instrument and N type female towards my transmitter (although data sheets of high end attenuators have sides per say in the datasheet )

anyway it was very helpful and enlightening ,

thank you for your time and effort and rely to my question

The_Spectrum.A_idiot

The_Spectrum.A_idiot:
Dear hfleming
Thank you very much for responding to my post ,

--- Quote from: hfleming on August 13, 2019, 11:26:56 pm ---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).

--- End quote ---
Fascinating box I may try to do that although for now that i am quite inexperienced with RF I would prefer a ready made commercial solution so that I won't kill anything by mistake ( as far as I know no warranty will cover idiot user mistake )

but still thank you so very much for your contribution

thank you for your time and effort and rely to my question

The_Spectrum.A_idiot

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