Tiny-CAT SCR Preselector  

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Tiny-CAT SCR Preselector

Software Controlled Radio preselector.

1.8MHz to 30MHz tunable Band-Pass Filter bank. Digital tuning.

Intended to complement radio projects due its modular design.

USB or I2C bus control options.



Tiny-CAT SCR preselector is connected in line between the antenna and your receiver or transceiver providing filtering of R.F.spectrum to reduce broadband signal energy into the receiver.

If the preselector is connected to a transceiver take precautions to prevent transmitting through it. An Input/Output by-pass dual power relay accessory is available to by-pass the preselector in transmission. FlexRadio user do not need external by-pass relay; see Owners Manual, Primary antenna ports configuration.

Suitable to work with any SDR or analogue radio.Tiny-CAT SCR preselector is remotely operated from a personal computer via USB over VCP by means of the USB control module option or from a radio or digital system supporting I2C bus data communication by means of the I2C bus control module option.

Operating modes:
Using the USB control module option: It works connected to a PC via USB over Virtual COM Port under Windows OS. Tuning and Band selection can be performed from:

- Its own Graphic User Interface (GUI) on PC.
- CAT protocol over Virtual Com Port (VCP), Kenwood TS-2000 protocol.
- Over the Internet or Local Network. (TCP/IP protocol).
See below Tiny-CAT SCR Preselector user manual for more details.

Using the I2C bus control module option:

From a radio or digital system supporting I2C bus remote control. On PowerSDR It works connecting the hardware to FlexWire socket on FlexRadio rear panel. Tuning and Band selection is done by means of an embedded control slider on PowerSDR under label "Heros". See below Tiny-CAT SCR Preselector user manual for more details.

Tunable BPF module.

USB control module.

I2C bus control module.

Technical features:
■ Tunable Band Pass Filter bank for HF Bands covering 1.8 to 30 MHz.
■ Five selectable bands.
■ Passive Band Pass Filters.
■ Removes strong signals radiated back to the antenna from SDR quadrature mixers.
■ No active switching or amplifier devices in the signal path, therefore it does not contribute to (IMD (Intermodulation Distortion).
■ High linearity (IP3). Suitable for Software Define Radios and analogue receivers.
■ Five Band Pass Filters: Tapped mono coil wound on large toroidal T-200 iron core avoiding saturation in front of large signals.
■ Digital tuning. Eight bits variable digital capacitor emulator.
■ 16 way IDC connector input for control signals and power supply.
■ Size: 157mm x 75mm. (6.181 x 2.953in).
■ USB or I2C bus control modules option.
■ Suitable aluminum enclosure option available.

  USB control module option.
■ Full speed USB v2.0 compliant.
■ Plug and Play feature.
■ USB type B connector.
■ Power Supply: 12V DC/250mA max.
■ Size: 61x50mm, (2.402 x 1.969in).

I2C bus control module option.
■ 16 bits standard I2C Bus serial bus interface. PCF8575 I2C controller.
■ Supports 100Kbits/s and 400kbits/s FAST I2C Bus protocol.
■ Auxiliary Input/Output ports to expand control signals.
■ Compatible with most microcontrollers.
■ Power Supply: 12V DC/250mA max.
■ Size: 70x46mm, (2.756 x 1.811in).

User manual

Tiny-CAT SCR Preselector user manual


Operating modes


USB version

Using the USB control module

Remote control from PC by means of its Graphic User Interface (GUI).




Graphic User Interface (GUI) on PC.

  GUI context menu .
See Tiny-CAT SCR Preselector user manual for details.

Graphic User Interface (GUI). Remote control console.

The control console application provides manual remote control from PC and a set of options.
It runs on PC under Windows OS. It is an executable file does not need to be installed.




CAT remote control. Tracking feature using USB control module.

Popular CAT (Computer Aided Transceiver), serial data communication protocol over Virtual Com Port (VCP) enables the Tiny-CAT Preselector to provide the user with a way to interface with several radios using third party software applications. The microcontroller on USB control module board decodes valid CAT commands into specific instructions to be executed. The user can remote operate the preselector from remote control applications running on PC.


CAT configuration console on PowerSDR

Internet/Local network remote control.

The Tiny-CAT preselector supports connections via the Internet and Local network.To make use of this feature execute the application on your computer and on a remote one.

The protocol only uses TCP/IP; UDP which by definition is unreliable is not used.


Remote Server console (Preselector side)

Remote client console (Remote side)


  I2C Bus version

Using the I2C Bus control module

The Tiny-CAT SCR Preselector I2C Bus remote control module version lets to handle it easily from any FlexRadio/PowerSDR.

Also from a custom made digital control system or radio project due the simple implementation of the I2C protocol on any microcontroller.


PowerSDR I2C remote control console

Tiny-CAT and PowerSDR

Tiny CAT SCR Preselector working in I2C mode with PowerSDR and FlexRadio.

  The Preselector control window includes band switch and tune slider. Also complementary control functions for Tiny Plus-CAT SCR Preselector are included.



Tiny-CAT SCR Preselector boxed option available.

Tiny-CAT SCR Preselector should be enclosed in a RF tight box due the antenna effect of its large coil that easily gathers nearby signals or noise.

The following pictures show Tiny-CAT SCR Preselector assembled in hardy aluminum enclosure from Hammond model 1455T1601.

Dimensions are: 160mm X 160mm X 51mm. (6.29 x 6.29 x 2 inch)

The USB or I2C bus boxed versions, ready to use contains:

- Tiny-CAT SCR Preselector.Band Pass Filter bank module and control module.
- USB or I2C control module option.
- USB cable. (USB control module option)
- CD ROM including user manual, software and USB driver for Windows Operate Systems.
- BNC-BNC coaxial cable tails.


USB or I2C versions front view

USB version rear view

I2C bus version rear view

USB version

I2C version


Optional Accessories

  Tiny-CAT SCR Preselector - Flexwire I2C bus interconnection cables (Shielded, EMI protection)  

Flexwire I2C bus boxed interconnection cable.


Flexwire I2C bus module interconnection cable.


  General Purpose Dual By-Pass relay

150 Watts RF power rating. PTT or Keying line activated.


It is designed to by-pass the Input and Output RF ports of any device in line with your transceiver or transmitter.
A typical application includes inserting between antenna and a transceiver or transmitter a preselector, preamplifier or filter device.
On transmission switchover, via PTT or Keying line, the Input and Output RF ports of the device are by-passed avoiding being overloaded.
Two switching configurations are available:
- Default By-Passed.
- Default NO By-Passed. (see below).

- Frequency range: DC - 60MHz
- Insertion loss: 0.2 dB @ 60 MHz
- Isolation: 60 dB @ 60 MHz
- Power rating: 150 W
- Impedance: 50 Ohm
- SWR: 1.22 @ 50MHz
- Diode protection.
- Power supply: 12 Volts DC/68 mA
- Switching time:
- Set: 15mS
- Reset: 5mS
- External Dimensions: 40x37x111mm.
- Connectors: SO-239 Antenna/RTX; BNC RX IN/RX OUT
- BNC-BNC coaxial tails and complete shielded control cable with snap-on RFI-EMI suppressor ferrite cores   are provided.

Dual Antenna Relay page   Relay page

  USB Galvanic Digital Isolator for SDR radios  
  The USB Galvanic Digital Isolator for SDR radios is designed to break the galvanic connection between USB host PC and the attached SDR radio peripheral avoiding that whatever power and ground noise from the PC side do not influence the sensible radio on the other side.
The resultant galvanic isolation improves common-mode voltage, prevents ground loops, a common cause of interference and data distortion issues, improves reception, as the noise floor in the receiver is lowered, and removes spikes and birdies on the PC panoramic screen. In addition provides isolation of 1000V AC between the host PC and the radio peripheral that guard against surges that may come from the antenna connected to the receiver.
The USB Galvanic Digital Isolator for SDR radios is based on ADuM 4160 Full/Low Speed 5 kV USB Digital Isolator and ADuM 5000 Isolated DC-to-DC Converter both from Analog Devices combining high speed CMOS and chip-scale air transformer iCoupler technology.
The USB Galvanic Digital Isolator complies with specifications USB 1.1, Low speed (1.5Mbps) and USB 2.0 Full Speed (12Mbps). The speed mode is set manually via two jumpers inside (default full speed). Most of the time it is not necessary change between modes but if automatic speed detection is desired, an external hub can be connected to the peripheral side configured for full speed.
The USB Galvanic Digital Isolator is self powered from the host PC through the USB cable. An embedded DC/DC converter provides a galvanic isolated voltage of 5VDC/100mA to the peripheral side. It includes additionally ESD, EMC protection of the data lines and power transient short-circuit guard.
It is highly advisable not to power any part of the connected radio from the USB bus, instead an external dedicated power supply must be used.
The USB Galvanic Digital Isolator behaves like an USB cable, no USB drivers are needed. It works on all operating systems, Mac, Windows, Linux, etc.

Isolation 1.000 Volts AC
Protection: EMC, ESD, Overvoltage Surge, Short-circuits.
Power supply:
- PC side: From USB cable, 5VDC. Attached signalling LED.
- Drawn power from peripheral radio max: Through USB cable, 5V DC/100mA.
USB modes:
Full speed (12 Mbps) Low speed (1.5 MBps). Switchable.
Standard socket connectors: PC side: USB type B, peripheral side: USB type A.
Dimensions 67 mm x 66 mm x 28 mm. (2.638x2.598x 1.102inch)
USB2 pair of cables included.
USB Galvanic Digital Isolator for SDR radios page.   USB

  Tint-CAT SCR Preselector .   Tiny-CAT SCR Preselector  

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