Jim's Electronics Laboratory

I enjoy designing electronic gadgets and useful tools.  It is my passion, my life.  In this webpage I present my work.  The fields I am more interested in are 'embedded systems' and communication systems (analog or digital).  When I started my carrier as an electronics engineer some 22 years ago,  I was focused on digital control systems, robotics and industrial applications but as years passed I got involved in RF circuit design and communication systems.  When I am not working,  I enjoy researching  ideas in my home lab.  I am also a licensed radio amateur operator with callsign SV1OBT

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Below you can see some of my projects.  This website is constantly revised and updated so dont forget to bookmark and visit again.

CG-1  Comb Generator

The famous (among ham radio enthusiasts) CG-1 Comb Generator.

This gadget is a very simple tool for those who do not own an expensive RF signal generator.  It is a battery powered comb generator producing RF signals from 100KHz up to 1.42GHz.  The emitted spectrum is full of 100KHz spaced signals in the mentioned range.

This spectrum can be used to measure filters, calibrate SDR or conventional radio receivers, produce reference signals in the lab or conduct reference measurements in EMC chambers.  The applications for a comb generator are too many to include here.  To get an idea of how the emitted spectrum looks like, check the image below.  It shows a portion of the spectrum (1MHz span, centered at 144MHz).  As you can see, there are tones every 100KHz.

Having a tone every 100KHz is cool but the coolest thing is to have calibrated signals so that you can use them as reference for useful measurements and experiments. 

So I chose 16 signals (one for each ham radio band) and some more, and measured the power level and frequency for each one of them.  The results were printed on a label and placed on the enclosure of the unit.  I have made a number of this units, and below you can see a typical calibration table

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Frequency (MHz),   Power (dBm)    Band that can be tested

1.900                             -46.6                         160m

3.600                             -42.1                         80m

7.100                             -38.9                         40m

10.001                           -38.2                         30m

14.101                           -38.1                         20m

18.001                           -38.1                         17m

21.201                           -38.5                         15m

24.801                           -38.9                         12m

28.401                           -39.7                         10m

51.003                           -46.7                         6m

90.005                           -52.3                         FM broadcast

125.906                         -59.0                         AIR band

144.907                         -66.6                         2m VHF

435.022                         -83.9                         70cm UHF

1295.967                       -97.2                         23cm 

1420.373                       -98.0                         Hydrogen line  (~1.44GHz is usually calibrated in latest units)

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I've done a couple of videos demonstrating this generator connected to a softrock SDR.  And I've written a user manual because I like to keep things tidy and in order.

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User manual:  CG-1 User manual v1.0

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You can read about the thoughts behind the development of this product in my blog.  This post is quite old now, but it captured the thoughts and ideas behind the design.

https://www.jel.gr/blog/?p=177

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Specifications

    •    Battery operated unit. (9v battery on a battery holder for firm mounting)

    •    50Ω RF Output

    •    Small, aluminum die cast box with reliable switch and quality SMA connector mounted on the box.

    •    RF shielded design to keep unwanted noise out and being able to produce very low power harmonic signals.

    •    Frequency range of harmonic content:  Every 100KHz from 100KHz up to 1.42GHz (to cover all HF, VHF, UHF, SHF bands)

    •    Power level range for calibrated signals:  Between -38dBm and -100dBm usually.  (differs a little bit between each serialized unit)

    •    Power level accuracy within 1.5dBm  (each generator has its own serialized calibration sticker with its measurements). Calibration is performed with the use of a lab calibrated 2cm rigit cable.

    •    Frequency stability:  20ppm crystal oscillator reference at 20MHz.

    •    Output signals are immune to supply voltage deviation due to battery draining.

    •    Being able to provide >100 hours of service with an alkaline 9v battery

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If you like this project and want to contact me you may use email 

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