DIY: HF/VHF Portable Mini Tuner de ON6MU

By Guy, de ON6MU

Schematic fig1

QRP mini tuner matcher

RE-AT2HF6/P Parts list

  • alu box of 70mm X 40mm X 33mm

  • 2 female PL 259 chassis

  • C1 = variable capacitor of at least 300pF or better 500 pF

  • S1 = 10 or more position rotary switch

  • L1 = 0,7mm insulated copper wire, 6 turns par connection closely together, 9mm outside diameter (8mm inside)
    taps every 6 turns and the last two sections (L1′ and L1”) 4 turns spaced at 1mm and 3turns spaced by 2 mm.
    The first two sections has a ferrite core inside.
    Could be that lower frequencies needs higher inductance, experiment with by adding a core in the last few sections (see fig2)

  • I added two bolts on the alu-box chassis to – if needed – connect the tuner to ground or for using a counterpoise.

  • R1: 1.5k carbon 1/4w (non-inductive resistor); optional to allow drain of possible static build-up on the antenna (or use a 10mH inductor)

  • R2: 2 x 470 carbon 1/2w parallel (non-inductive resistor); optional to have some little protection during switching when using a carier, as the switch could open the the connection for a fraction of a second during switching.

The coil

  • Wind 6 turns x – 2 connections on your switch (in this project a 10-position rotary switch is used, being 8 times 6 = 48 + 4 + 3 = 55 turns) over a 7mm screwdriver (or simular obkject hi) and make a tap every connection. Solder each tap.

  • Solder each tap to each connection of your switch and stretch L1′ (being 4 turns) at 1mm spacing and L1”(being only 3 turns) at 2 mm spacing. You can replace L1” by 3 turns of silver wire to allow better Q on higher frequencies (VHF).

  • Minituner insides…


  • Alex VE7DXW changed 5 of the lower 6 wdg air coils with 1 wdg, 2wdg, 4wdg, 4wdg, 6wdg ferrite core coils, which gives higher L values
    Thanks Alex!


  • manual operation

  • frequency range (depending on the coil min & max inductance):
    (Up to 150Mc if: L1” is silver(plated) wire, High Q switch, minimum capacitance of C is small enough and close connections are used in respect to 50 Ohms impedance)

  • 10 Watt +-

  • direct feed through

  • small and compact design ideal for low power QRP transceivers, like the Yaesu FT-817, or of course for receivers…

  • connection for counterpoise/ground

If you elect to use an antenna tuner, it is extremely important that you understand exactly how to use tuners and what they can and cannot do. A few watts of RF can easily become lost in an incorrectly adjusted antenna matching device. The whole idea of a QRP station is to keep things simple and economical, so I cannot overemphasize the priority of a clean, efficient connection of the amplifier output to a resonant antenna.


Homemade aluminum box



New SDR# plugin “LevelMeter”

LevelMeter is a plugin for SDR#

There are three modes to monitor the rx power

  • rx power of VFO frequency
  • average rx power in Bandwith
  • peak rx power in Bandwith



to get the plugin running:

  • Download and unzip the package
  • copy SDRSharp.LevelMeter.dll into the SDRSharp direcotry
  • edit SDRSharp.exe.config
  • goto sharpPlugins section and add one line as described below


Find source code here LevelMeter Plugin Source Code

Airspy: tiny (5×3 cm) software defined radio capable of sampling 10MHz!

Airspy is a very tiny (5×3 cm) software defined radio capable of sampling 10MHz of spectrum anywhere between 24MHz and 1.7GHz. It is the fruit of countless hours of head scratching, fiddling and experimenting with the cutting edge Radio and DSP technologies. The early prototypes gave such an unexpected satisfaction to us and our friends, that we decided to give it a chance to survive commercially.





Technical specifications:

  • 24 – 1750 MHz RX range
  • 3.5 dB NF between 42 and 1002 MHz
  • 12bit ADC @ 20 MSPS (80dB SFDR, 64dB SNR, 10.4 ENOB)
  • Cortex M4F @ 200 MHz and up to 204MHz with Multi Core MCU (dual M0)
  • 1.5 ppm clock
  • External clock input (10 – 50 MHz)
  • 10 MHz panoramic spectrum view with 8MHz alias/image free
  • IQ or Real, 16bit fixed or 32bit float output streams
  • No IQ imbalance, DC offset or 1/F noise at the center of the spectrum
  • Extension ports: SGPIO, 2 x ADC channels, 2 x programmable clocks

Possible usages:

  • Spectrum Analyzer,
  • Fast scanner,
  • Radio surveillance,
  • Direction Finding,
  • Passive Radars,
  • ADS-B,
  • FM Radio,
  • Analog TV,
  • Digital Terrestrial TV,
  • Ham Radio,
  • Heck, this is a software defined radio! The only limitation is your imagination :-)

May be you will want to get one or two boards to experience the joy of listening to the radio waves like nobody did before and with software you can hack by yourself? Then register so we can let you know when the product is ready for purchase! Our special thanks to the all folks who helped debugging and improving the project.



SDR-Radio V2 RTL-USB (How-To)

Simon was gracious enough to provide directions to build a DLL to directly support the RTL Dongle in his new V2 application.  In an effort to help others out I have followed his directions and built the DLL to make it available to those who do not have the required development tools.  I used Microsoft Visual Studio 2010 and the following source code:

I followed the directions at:

In the zipfile you will see two directories:

If you are using a 64bit copy of windows you will need to copy the files in the 64bit directory to the following location:

C:\Program Files\

For 32bit windows copy them here

C:\Program Files (x86)\

Here is a link to the DLLs. Jan 6th 2013 Feb 9th 2013
Here is a screenshot running my RTL Dongle listening to a local FM Radio broadcast.


RTL-SDR: Passive radar with $16 dual coherent channel receiver

My previous post describes the $16 dual channel rtl_sdr dongle hack. In the last few days I’ve done some more testing and it turns out I can use the system for passive radar! I didn’t expect this, because the receiver only has 8 bits and passive radar requires a lot of dynamic range.

Airplanes and occasional specular meteor echoes.

I hooked up the two channels into yagi antennas that we have used with Echotek and USRP receivers for passive radar. One of the antennas was measuring the transmit waveform, and the other was measuring the echoes. I ran a measurement, and to my great surprise, it worked just fine.

I did tweak the signal levels a bit in order to ensure that I optimally use the dynamic range. I also had the bandwidth set to 2.4 MHz, giving me about 4.5 bits extra dynamic range after filtering the signal to 100 kHz in single precision floating point.

Two log periodic antennas used to passive radar with the dual coherent RTLSDR R820T dongle.

This really does give us a glimpse of the future where high end digital receivers will cost $10 per channel. The low end ones are already in that price range. Think of all the potential science that can be done!