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Arduino-LevelMod.php    22424 Bytes    04-06-2024 20:10:37

Arduino/Genuino "LEVELMOD"

A Microwave Powermeter from DC to Daylight (9 kHz ... 40 GHz)

The assembled prototype ... without a Detector :-)

✈ Motivation

In our experiments, it is often necessary to lock something on the amplitude of a carrier / sideband. Sometimes it is necessary to monitor the presence of a signal, like the 10 MHz Frequency Standard. In both cases, this - remote controlled - Powermeter can do the job.

And yes, we don't use 40 GHz, but Linear Technology was so kind to send free samples. Sharp tongues would say, that I used this "proof of principle" to build a Radarduino :-)

The date printed on the frontpanel was way too optimistic. This project was released to public on the first HAM RADIO (Friedrichshafen) after Covid-19, 25.06.2022.

✈ The Design (Display-Unit)

To make things easy, we split the design into a Display-Unit and several Detector Units. By that, the measurement plane can always be brought close to the source to be measured. And we have a 'Specialist' for every Measurement-Job. Below is the Block Diagram for the Basestation.

Block Diagram Levelmod

The Basestation mainly consists of the Arduino Nano Every. A DC/DC converter generates the +12V and the -12V needed for the Opamp on the Detectorboard. This is done by an R1D-1212, capable of delivering ± 42 mA

In Version 2 we added a Voltage Regulator to stabilise this +12 V down to +9 V, as the Voltage Regulator in the Detector (which is used as a Reference for the A/D Converter) seemed to have an insufficient Line-Regulation.

As there was some space left, we also put the venerable MAX232 with a DSUB connector on the Board. Even so, the preferred methode is a usb connection.

As the supply voltage is critical (due to the DC/DC converter), the Arduino monitors it.

On the Detectorboard, an Opamp amplifies the raw RSSI signal (which is produced by the often installed logarithmic amplifier) and makes it available at a BNC connector on the Basestation. It is also digitized by a LTC2485 (24-Bit ∆Σ ADC). The Pullup - resistors for the I2C lines are placed on the Detector side. By that, the Base has several ways to see, if a detctor is connected. First it can measure the raw RSSI level, second it can measure the voltage level on the SCL and SDA lines.

Arduino Levelmod

Really not much inside. The magic happens is in the Sensor. And in the Software.

✈ The Connector

We use a KFV 60 (DIN Audio / Video Connector, 6 Contacts, Jack, Panel Mount, Solder, Silver Plated Contacts) from Lumberg (Farnell Order Code: 1193069) and a SV60 (DIN Audio / Video Connector, IP40, 6 Contacts, Plug, Cable Mount, Solder, Silver Plated Contacts) from Lumberg (Farnell Order Code: 1321478).

1SCLPull-up on Detector side
2SDAPull-up on Detector side
3RSSIDetector ouput, amplified, Vu = 3
4- 12 Vunstabilized, max. 40 mA
5+ 9 Vstabilized, max. 40 mA

✈ The Calibration

Every Sensor has its own calibration data stored on an onboard Eeprom. This data contains :

0x002Type of Sensor, e.g. 8307, unsigned int
0x022Serialnumber, e.g. 0099, unsigned int
0x044Reference Voltage on Sensor, e.g. 5.024 V, float
0x084Minimum Frequency in MHz, e.g. 1.0, float
0x0C4Maximum Frequency in MHz, e.g. 500.0, float
0x104Minimum Level in dBm, e.g. -70.0, float
0x144Maximum Level in dBm, e.g. +10.0, float
0x184Slope @ Frequency[0], float
0x1C4Intercept @ Frequency[0], float
0x204Slope @ Frequency[1], float
0x244Intercept @ Frequency[1], float
0x784Slope @ Frequency[12], float
0x7C4Intercept @ Frequency[12], float

The intermediate frequencies are calculated by a fixed scheme. (Other schemes mayst be used as well). From the minimum frequency (0x08) and the maximum frequency (0x0C) the difference is calculated. The delta-frequency is a fraction of the difference frequency. We use the following steps :

10%    10%    10%    10%    10%    10%    10%    10%    8%    6%    4%    2%

With Fmin = 1.0 MHz, Fmax = 500.0 MHz, we get a Difference of 499.0 MHz. The calculated Slope and Intercept values therefore refer to the following frequencies :

F[0] F[1] F[2] F[3] F[4] F[5] F[6] F[7] F[8] F[9] F[10] F[11] F[12]
1 51 101 151 201 251 300 350 400 440 470 490 500

Calibration is done with a trustworthy Synthesiser and a Worksheet (Excel) or another Calculation Suite of your choice. See the examples in the Detector Section. For every Frequency, a pair of slope and intersection values is calculated. These values can then be beamed up to the Eeprom via a serial link.

While Eeprom is empty, the Voltage is displayed
Cover only opened for Fotomodel :-)

The Calibration of new Sensors is like a 'Kindergeburtstag', using the menu offered :-)

Sensor Overview

The Frequency Coverage of 'some' Sensors, beeing in the budgetary Range

✈ The AD8307 Detector - Type 8307

AD 83079 kHz ... 500 MHz-60 dBm ... +10 dBm

This is the workhorse of a lot of RF-Powermeters out there. So we cannot write much new things and therefore let a picture speak. The case is a Sucobox.

Inside view of the Detector

✈ The LT 5537 Detector - Type 5537

LT 553710 MHz ... 1 GHz-70 dBm ... 0 dBm

This Detector is almost identical. Just in green. We also replaced the AD8307 by an LT 5537. The case, again, is a Sucobox. Around the logarithmic Detector are some 0402.

Inside view of the Detector

✈ The AD8318 Detector - Type 8318

AD 831810 MHz ... 8.0 GHz-60 dBm ... 0 dBm

High accuracy: ±1.0 dB over 55 dB range (f < 5.8 GHz)
Stability over temperature: ±0.5 dB

Inside view of the Detector

As we got hands on a bunch of different (broadband) diode detectors, a second website was created, dealing with them. The Arduino Sketch was expanded to also apply a different handling scheme.

✈ Test Sketch for Arduino/Genuino Nano Every

As the code is long - and the copy & paste procedure causes additional challenges, the file is provided as a download. Exactly here.

✈ Remote Control of the Levelmod

Arduino Levelmod

And that's the view, if a sensor is connected ...

Arduino Levelmod

Thanks to Andi and his Team, the view from behind is also aesthetically pleasing.

✈ Share your thoughts

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t1 = 6585 d

t2 = 200 ms

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