Pre-Selector Manual Control

Building a multi-band receiver for HF? Or an HF up-converter for SDR?

Then this HF Ham-Bands Pre-Selector Module can be used to enhance reception performance on all amateur radio frequency bands by significantly reducing the signal strength of most unwanted signals outside those frequency bands and greatly improve IMD response. If you have never used a filter before your HF upconverter for SDR you can immediately see that it greatly improves receiver performance on the wanted frequency band by rejecting most unwanted.

The design uses RF type 5V DC relays to activate one band-pass filter every time, as selected by the control connector pins.

Each band-pass filter uses 2 variable shielded inductors and 3 capacitors. You can see their frequency-gain response below, after proper inductor alignment.

For even better results you can easily cascade two of those modules and use one HF pre-amp between them.

Except of selecting one of the 9 band-pass filters, one for every amateur radio bands for HF, a by-pass function is available to switch out the preselector, if reception to any out of bands signal is needed.

In addition, any external fixed or variable attenuator can be switched in or out  at the input, using an on-board relay and SMA connectors and any external pre-amplifier can also be switched in or out of the circuit after the filters.

Hand-operated selector type switches can be used and any type of micro-controller interface, as 2N7002 MOSFETS are used for driving the relays.

The relays are powered from a 5V DC input, while the selection is done by applying a 3.3V high to each MOSFET's gate. Remember to apply LOW (or 0V) to de-select before or after selecting another filter. Every relay needs about 30-50 mA so the total current per module for the 5V supply can be 150 mA max if the Attenuator and Pre-Amp relays are energized altogether.

ORDERS For a complete PCB Module EUR 63.80

​The prices do not include 24% Greek VAT applicable only to individual buyers from European Union. 

The Module includes a  high-quality ENIG FR4 PCB (180 x 50 mm) that comes with all  components factory pre-soldered. 

RF capacitors are used for all the circuits.  High Q inductors and RF relays are used.

Six SMA female connectors are also soldered in place.

The shipping cost is USD 12.00 with registered mail  (your signature is required upon delivery). 

We usually ship the next day and it takes about a week to 10 days for USA or Australia, less than a week for Europe.​

The preselector module in "by-pass' position, showing 0.5 dB insertion loss (left) and the 160m filter response (right).

HF Amateur Bands Preselector

Provision for external pre-amp and attenuator control.

9-bands (160m - 10m) and by-pass function.

RF relay switched band-pass filters with DC wetting.

12m band frequency response (left), 10m band (right).

17m band frequency response (left), 15m band (right).

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Current boards include the pull-down resistors on the PCB close the FET gates and it is not necessary to place them on an external switch.

The 80m band response (right) and the 40m (left).

30m band frequency response (left), 20m band (right).