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HF Amateur Bands Preselector
Provision for external pre-amp and attenuator control with relays and SMA connectors for switching them in/out of circuit.
10-bands (160m - 10m with 60 m included) and by-pass function
RF relay switched band-pass filters with DC wetting
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 10 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 - 5 V (logic 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 can be 150 mA max if the Attenuator and Pre-Amp relays are energized altogether with one band relays.
ORDERS For a complete DIY KIT
The KIT 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 is with registered mail (your signature is required upon delivery) or with FedEx as you select during the check-out steps.
For more pictures, schematic etc please visit https://www.sv1afn.com/ham_band_presel.html (copy and paste to your browser).
Check out my other items! I always combine shipping.
AN ANSWER TO A BUYER, MAYBE OF HELP TO OTHERS TOO:
The preselector has 10 filters, one "through", which means "filters out" position and 2 more I will explain later.
You select one filter to be included into the receive path if you simply send a logic HIGH to its individual pin of the connector J9.
For example, if you send a HIGH (3.3V or 5V) to pin 1 of J9, the 10 m band filter is inserted. You should take care to keep all other inputs at logic LOW.
For powering with DC, you apply +5V to pin 14 and GND to pin 15. Nothing else is required. The 3v3 and 12V positions are there as a binding post to help your cabling sharing DC power to LNAs or attenuators etc.
For the 2 more inputs, the first is selected to insert a preamp in the receive path and the second to insert a fixed or variable attenuator.
Again, apply HIGH to select.
I wish my explanation was helpful, if you have any question please email me.