10dB attenuator

The attunator that is shown here has a damping of 10dB that means it turns the 30mW output of the BS11 into 3mW output. Please note that 10dB is only an example. The attenuator is designed to be configured to any damping factor.

The first thing you should do is calculating the resistor values here:

Resistors values can be calculated at:

The values you get will not match to the resistor values you can buy. That is the reason why the PCB has 3 resistors in series to form one of the resistors you have calculated with the script.

When everything is tested twice you should seal the attenuator with a HF-Tin. I used a commercially available HF-tin-box-cover. Please note that on the photo only the corners of the tin are soldered. That is because the attenuator was just in the development phase and we easily wanted to be able to remove the tin to recycle the components.


Our testcase was a spectrum analyser with an atenna and the BTS in the other room. All tests were done with the original antenna. Our first test was without the attenuator:

And now with the attenuator:

As you can see the signal was decresed at about 10dB.

Note: The Attenuator has been also tested with a network analzer. See the attachments for measurement results (S-Parameters). There is to mention that the attenuator is not really a high quality HF-Device. The SWR is at 9 and the attenuation is about 7db. I guess that this is an impedance problem since the resistors in the attenuator are not exact enough.

But the BS11 (and other industrial grade HF-Equipment) is equipped a circulator (Sometimes also called insulator, see also which prevents waves to enter the PA from outside. That is also true for reflecting waves. So everything that is reflected by the attenuator is fired into the internal dummyload of the BS11. If you run the BS11 with about 30mw the internal protection circuity will tolerate such reflection.

So this attenuator is not high quality, but it works.

Eagle-Files / License

For eagle and CNC-Files see the attachments. The license is Beer(hard)ware ;-) Club-Mate is also accepted.

Files (17)
10dB_attenuator.jpg View 10dB_attenuator.jpg 294 KB dexter, 12/02/2009 11:21 PM
attenuator_layout.png View attenuator_layout.png 16.5 KB dexter, 12/02/2009 11:31 PM
attenuator_schematic.png View attenuator_schematic.png 10.5 KB dexter, 12/02/2009 11:31 PM
with_attenuator.jpg View with_attenuator.jpg 227 KB dexter, 12/02/2009 11:43 PM
without_attenuator.jpg View without_attenuator.jpg 272 KB dexter, 12/02/2009 11:43 PM
10dB_attenuator_sealed.jpg View 10dB_attenuator_sealed.jpg 351 KB dexter, 12/02/2009 11:44 PM
attenuator.sch attenuator.sch 45.5 KB dexter, 12/02/2009 11:49 PM
attenuator.brd attenuator.brd 8.86 KB dexter, 12/02/2009 11:50 PM
attenuator.plt attenuator.plt 14.6 KB dexter, 12/02/2009 11:50 PM
s11_Att.jpg View s11_Att.jpg 51.4 KB dexter, 12/18/2009 06:40 PM
s11_SWR_Att.jpg View s11_SWR_Att.jpg 45.8 KB dexter, 12/18/2009 06:40 PM
s12_Att.jpg View s12_Att.jpg 45.3 KB dexter, 12/18/2009 06:41 PM
s12_Mag_Att.jpg View s12_Mag_Att.jpg 47.4 KB dexter, 12/18/2009 06:41 PM
s21_Att.jpg View s21_Att.jpg 45.2 KB dexter, 12/18/2009 06:41 PM
s21_Mag_Att.jpg View s21_Mag_Att.jpg 46.5 KB dexter, 12/18/2009 06:42 PM
s22_SWR_Att.jpg View s22_SWR_Att.jpg 46.2 KB dexter, 12/18/2009 06:43 PM
s22_Att.jpg View s22_Att.jpg 51.4 KB dexter, 12/18/2009 06:43 PM

Updated by laforge about 8 years ago · 15 revisions

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