Vorläufig / Preliminary, work in progress
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RF Attenuator Digital
In order to measure easier the response curve of RF modules I bought this 0.5 dB step digital attenuator. See the picture on the right.
The 30 dB version is the best buy, to measure up to 2.4 GHz. Now there is a new updated version with 0.25 dB stepping, see at the links.
There are 3 Models:
- ATT-30 Series: Attenuator Attenuation Range (0-31.5 dB)
- ATT-60 Series: Attenuator Attenuation Range (0-63.0 dB)
- ATT-90 Series: Attenuator Attenuation Range (0-94.5 dB)
The Features are:
- the operating frequency: LF - 3 GHz
- the attenuation adjustment range (Model): 0-30 dB, 0-60 dB, 0-90 dB step
- the attenuation step: 0.5 (dB)
- insertion loss: ≤ 3.5 dB
- standing wave ratio: ≤ 1.4
- Attenuation accuracy: ± 1 dB max.
- Rated input power: 1 W = 30 dBm
- Connector type: SMA
- Temperature range: -10 ℃ ~ +50 ℃ (operation) -40 ℃ ~ + 70 ℃ (not running)
- Overall dimensions: 55 X 40 X 16.5mm
- Weight: 57g
- Input and output impedance: 50 Ohm
- The attenuation value is stored in EEPROM (found out)
S1 ">": right cursor
- S2 "+": the value of the cursor bit plus
- S3 "OK": Confirmation (after the data is changed, you need to press the confirmation button)
S4 "<": left shift cursor
- S5 "-": the value of the cursor is reduced
- OLED display:
- upper line: Attenuation value
lower line:Fre:3,000,000KHz (not changeable)
Remote Control (corrected):
- Baudrate: 115200 8N1
- wv0 command: set the attenuation value
- The format is: wv0xxx + 0x0a, a total of 7 bytes;
- Where "xxx" is the attenuation value represented by 3 digits, such as:
- wv0115+0x0a(LF): Indicates that the write attenuation is: 11.5 dB (maximum attenuation: 0-315, step is 5)
- Converted to hexadecimal: 0X77 0X76 0X30 0X31 0X31 0X35 0X0a
- rid command: read the version ID
- the PC sends "rid + 0x0a", the machine returns the model ID, e.g "ATT-60"
- Note that there is a line feed "0x0a" or '\n') at the end of the string.
There is a Python3 program as an example, see Attenuator-60dB.py
After opening the housing, I realized that the labels of the IC's was sanded off. See the photo above.
Fortunately there are only some attenuator IC's on the market. When you search the internet for PEREGRINE_HF-Switch-PE4302_EN.pdf you will find the data sheet. There is also a second source F1912 from company Renesas. Because of the 10 KOhm resistor on pin 3 it could be only the PE4302, see page 5 of the data sheet.
Operating frequency: At the figures of the data sheet you see that the linear range of the parameters are only good up to 2200 MHz. Also stay with the environment temperature close to 25 °C to keep the error small.
Insertion loss: up to about 100 MHz the value is about 1.2 dB. At 2500 MHz it is then about 1.5 dB.
Attenuation Error vs. Attenuation setting: See figure 8 in the data sheet. Up to 1 GHz the error is less than -0.5 dB. At 31.5 dB the error is -1 dB above 2.2 GHz.
Considering that, it makes only sense to buy the 30 dB version. If you need more attenuation add fixed value attenuators.
2020-11-13 Now having a Vector Network Analyzer nanoVNA-V2 (480x320 pixel display) which works up to 3 GHz, I wanted to measure the frequency response of the new 30dB attenuator Link 3.
See the screen shot on the right, which shows a measurement from 0.01 to 3000 MHz.
The nanoVNA-V2 was calibrated for the same frequency range.
It can be seen, that up to 1.5 GHz the frequency response is linear (CH1 LOGMAG).
With that in mind it is hardly understandable the advertising with a frequency range of up to 3 GHz.
At an attenuation of 30 dB the frequency response looks very similar to the 0 dB attenuation.
See the screen shot on the right.
In order to see, if the frequency response is linear in the range of 0.01 to 1500 MHz I measured several points and created a spreadsheet in order to see, if the amplitude loss over frequency can be compensated by a formular.
The attenuation setup was 0 dB.
Yes, the function is about 1.5 dB loss per GHz.
f(x) [dB] = -0.00147 * x - 1.252 dB .
There is no DC blocking (about 70 Ohm, IN to OUT), so avoid DC voltage at the input.
At the maximum attenuation of 31.5 dB, you have an Attenuation Error at 2.4 GHz of about 1 dB. See the data sheet for more details.
The 30 dB version is the best buy, if you measure above 500 MHz.
Now there is an updated version (0.25 dB step) on the market, probably with the IC PE43703, see at the links. This IC is now obsolete and replaced by the IC PE43713.
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-- RudolfReuter 2020-05-26 17:52:29