HF preselectors or multi-band filters

[cybergibbons]

My primary SDR at the moment is an SDRplay RSPdx which has some good switchable filtering inside it. I think it's very similar to half of the RSPduo, shown below.


But I also run other SDRs that don't have this, and was considering using some band pass filters for HF.

What solutions are there here?

I've seen the following so far:
Heros Technology SCR-CAT - this looks very well made. The block diagram shows it has some interesting features, like the tunable bandpass, and the relay to allow you to switch in an external filter. Not keen on the way that the PIC micro side is closed source. Expensive, but refined and in a box.

Tunable Tiny Preselector from Heros Technology Ltd

Tunable,1.8MHz-30MHz Tunable Tiny preselector

www.herostechnology.co.uk

Tiny HF Preselector - interesting design. Looks like a single shared core for all inductors? Much cheaper. No case, but relatively refined. Not tunable.

HF Tunable Preselector

HF Tunable Preselector

www.herostechnology.co.uk

JaniLabs HF band Multi Band Pass Filter - simple design, no logic so that would need to be implemented. Uses PIN diodes for switching, so maybe insertion loss will be higher than with a relayed based device?

HF band Multi Band Pass Filter

Then there are some on eBay that are relay switched. Not really enough detail there to spend that amount of money without some specs.
Ebay 1
Ebay 2
Ebay 3

And then there is this oddity on Aliexpress and Amazon. You need to wind the toroids yourself, and no active switching.
Weird board
So has anyone got any systems set up for this? How are you controlling it?

 

[Dirk_SDR]

Interesting post!
I'm also searching for a preselector.
SV1AFN also made a good one I think:

HF Amateur Bands Preselector (new: NOW INCLUDES 60 m Band)

HF Amateur Bands Preselector (Built & Tested PCB Module with aligned inductors) USE A BAND-DECODER AND INSTALL THE PRESELECTOR IN ANY RADIO The Module includes a high-quality ENIG FR4 PCB (180 x 50 mm) that comes with all components factory pre-soldered. RF grade capacitors are used for...

www.sv1afn.com

 

[cybergibbons]

Thanks - looks interesting. The choice of bands is interesting on that one - tending towards the shorter wavelengths! Ideally I'd like to see 80m and 40m as well!

 

[kellogs]

Right. They all are, however, HF or up until 60 MHz in the best case. Dozens of them, too.

There is a whole world of radio these little dongles can sniff - if only they would not overload. The real deal would be those nice 60+ MHz filters - nowhere to be found

 

[prcguy]

I have the Janil filter and it’s a switched low pass. It works ok but the insertion loss is a little higher than I would like. A local ham club bought some SV1AFN filters to put inline with their Icom 7300s and they are band pass and seem to be a better filter for an SDR.

 

[kellogs]

SV1AFN filters are rather narrow; I do not suppose the built in RSP1 filters would be any good to use with a LNA for avoiding IMD. Is there a general rule of thumb as to what % of their center frequency should the pass band be ?

 

[merlin]

I would be going with the Heros preselector, the best of both worlds. Tunable is a real plus.

Is there a general rule of thumb as to what % of their center frequency should the pass band be ?

Industry standard is 7 bands from 1.8 to 60 MHz. seek out the best 'Q' you can find.
For step attenuation, 3 Db per to 30 Db would be my design.
Maybe put the FM trap ahead of the LNA.