RF Preselector or not? tiny SCR Heros Tech. Icom DIGISEL Yaesu VRF Harris RF-551A

RF Preselector: New tiny SCR Preselector 1.8MHz to 30MHz Tunable Band Pass Filter Assembled and kit versions. – tiny SCR Preselector (SCR) Software Controlled Radio via USB or I2C Bus (16 bits standard I2C serial bus interface) Made by Heros Technology Ltd in the United Kingdom.
It can be looped between RX OUT and RX IN of the HF Trancseiver, or SDR Receiver.  – A large toroid core T-200-7 is used, the large core offers a non-loaded Q (efficiency) value. A five bands tuneable Band-Pass Filter bank make up the core of the tiny SCR Preselector, and five telecom grade relays for band switching are connected to its corresponding section of the coil through the Band Selector control on the program software

See the Links and  following image – Preselector or not? Icom Digisel, Yaesu VRF ….

tiny SCR Preselector -  Available bands: • A) 1.8 MHz to 3 MHz • B) 3 MHz to 5.5MHz • C) 5 MHz to 10 MHz • D) 10.5 MHz to 21 MHz E) • 16 MHz to 30 MHz. -
A carefully PCB layout design and strong L/C decoupling prevent stages to couple in to each other improving the stop band response and filtering noise from control lines. – The program performs the task of adding or subtracting capacitor values in binary fashion in direct relationship with the tuning control on the program software. Increments or decrements are done in steps of 1pF. – The USB Control Unit is located in a separate module board to avoid introducing noise generated by the microprocessor itself and the noisy USB bus. – The (GUI) software: CD ROM including all software and USB driver for Windows Operate System

Transmission/Return loss of each Band response Plots and other features, and Price:
Link to: Heros Technology co. uk tiny SCR features

Sweep 0 – 30MHz Band and DIGISEL Plotter at 14.1 MHz (click to enlarge image) – The IC-7700 DIGISEL or Yaesu VRF function is similar to outboard tiny SCR Preselector. It has a -6 dB BW of 500 kHz at a centre frequency of 14.1 MHz Ham Band!
IC-7700 DIGI-SEL Insertion Gain & Bandwidth? there is a interesting test on VA7OJ’s website

Link to: IC-7700 DIGI-SEL test by VA7OJ’s

RF Preselector or not?
[Note-1] The outboard tiny SCR Preselector is single-pole, is similar to Icom DIGISEL Preselector or Yaesu VRF Preselector, and have a -6 dB BW of 500 kHz at a centre frequency. These types of preselector (single-pole) provide outstanding protection against OUT-OF-BAND interference, with a bandwidth much narrowe than the standard RF BPF UNIT “fixed bandpass filter networh” – Adding the single-pole preselector can be particulary useful if your station is located near a broadcast station, or if you use Dual Receive a lot in a “multi-trasmitter environment”

[Note-2] Tuned 4-pole preselectors type, typically with motorised air-variable capacitors and air-wound inductors to avoid saturation IMD, have been used in RN shipboard HF installations for yonks, long before the advent of DSP! – See the image HARRIS RF-551A

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