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I also was a noob some time ago. I also learned by asking questions.

Which attenuator you would like to buy depends on what signal strengths you would like to measure. If you are connecting a +11dBm signal to the input of a 10dBm attenator, then you the meter will have to cope with +1dBm of power, which is in the non-linear section. In that case I would use a 20dB or 30dB attenuator. 

An attenuator absorbs the power it attenuates and turns it into heat. That is why there is a radiator around it. Attenuators without a radiator are for low power only. So be sure to check the maximum power rating of the attenuator before buying it. If you want to measure a transmitter 10W (40dBm) signal you have to use a at least a 50dB attenuator to get to -10dBm for the meter. But the attenuator will have to dissipate almost 10W into heat. Which is a lot, therefor it will have a radiator, not a smooth casing like the low power ones.

I think it is a bad idea to add a radiator at later stadium because the heat conductance will be worst than one with an integrated radiator. Even when using heat conducting paste. The attenuator might get to hot on the inside too fast and get damaged. Which might result in wrong measurements without knowing.

What kind of signals do you actually like to measure?

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First, I already ordered the ImmersionRC RF meter v2 version which is supposed to have an internal attenuator.

But I still want to build my own DIY version for me and some for my friends, so that means I need that attenuator anyway as well.

I went down this “what is my RF value” path because I had some terrible issues with my Turnigy i10 transmitter, I get hit by failsafe a lot, in less than 200 meters and after getting my quad behind some small buildings. My transmitter is supposed to output less than 100mW to comply with EU regulations, but I believe it is actually doing even less.

I bought a small/cheap 2.4G booster and I want to compare RF power with original transmitter and with included booster, and obviously I want to see if I get any improvements.

if the cheap one turns out to be a bad upgrade (not enough output power) to get a decent flying then I plan to buy another booster which is like 2W advertised but from other people testing looks like approx. 1W output power.


But that is not all... I also have some tiny VTXes (im into micro quads) and I would like to see if they are able to output at the exact specs like 25mW or 200mW. I know those are small values and cant require big attenuations, just saying...

At last, even if I lack knowledge with RF stuff, I still love making small tiny antennas, but without no way to measure those feel like its a bit useless...


this is one 5.8GHz antenna I’ve built, on RG178 wire:




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I like that antenna, nice job.

When measuring 200mW (23dBm) signals you want to use a 30dB or 40dB attenuator. But when measuring the 2W (33dBm) booster you will need a 40dB attenuator at least. 

Using a 20dB attenuator will damage the meter. The attenuator will have to dissipate around 200mW or 2W.
Something like this will do 40dB / 5W attenuator to measure 2W
For 200mW this one will do 30dB / 2W

But you can also put one 10dB and one 30dB of the cheaper ones in series to get 40dB.

If you are going to connect the antenna directly to the meter you do not need an attenuator.

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When looking for a direction coupler what should I look for besides the frequency range it is supposed to work with?

I see this shop (with obscene prices and even more obscene shipping costs to me):



It also has something like a graph, how this graph is interpreted? Should it be flat for the range I'm testing?

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Hello, the project's zipped firmware file set is unavailable, is there any way to download the file set? 

The arduino code is available here (Aug-08-2017 post):  https://www.rc-cam.com/forum/index.php?/topic/4139-diy-rf-power-vswr-meter-low-cost/&do=findComment&comment=29002


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