I have my basic ubitx working nicely, i just wish the cw filtering was a bit (lot) better.  What is the best way to improve the cw filtering and narrow it down.   Dave c

Easiest is to add an audio filter of some sort between the phone jack on your uBitx and your headphones.
For most of us, easiest means best.

Strong adjacent signals will cause audio distortion, for this reason somebody looking for the ultimate in performance
will want a separate crystal filter for the uBitx.  This is moderately easy to do, but be prepared to learn about
building crystal filters and how to modify the firmware on your rig.

A discussion of CW filters can be found here:  https://groups.io/g/BITX20/topic/32840565

Jerry, KE7ER

First, the design is such that its not easy to insert a crystal IF filter for cw and retain ssb.

No worry, the gain distribution is such that an audio filter works nicely. I use a NESCAF. There are many options, I suggest one that has a audio amplifier at its output. I use my nescaf external,  but may put it inside. I don't find that I need its center frequency control nor need to bypass it, so it will just be adding the bandwidth control to the case.

Yes you can keep your ubitx basic as I am, or consider the jackal.

Curt wb8yyy

As curt said the NESCAF is a great cw filter and fun to build. They are kitting them again as well. Great value for the price and one of the few CW filters where the whistle at the narrow setting is almost non existent.
 73
--
David

 N8DAH
Kit-Projects.com

Shop is open!

I'm using the SotaBeams CW model which has as a bonus a signal that can light an led when you are well tuned.
     Bob  KD8CGH

On Thu, Oct 17, 2019 at 11:39 AM, <dgclifford@...> wrote:

I have my basic ubitx working nicely, i just wish the cw filtering was a bit
(lot) better.  What is the best way to improve the cw filtering and narrow it
down.   Dave c

Dave,
Here is a simple circuit that I have been using and find that it works quite well for both CW and SSB. It is a variable bandwidth filter, based entirely on the circuit developed by Andy, RW9RN (thanks, Andy!!). It uses the MAX7400 switched-capacitor filter (SCAF) chip, common (I am told) in the telecomms industry. Component values are ones I had on hand and are all close to values suggested by RW9RN. It runs on 5VDC but needs a 12V reference as well, as you can see in the schematic. The pot controls the bandwidth. Connect the circuit input to the audio output of your uBITX and plug your phones or speaker into its output. Mount it either internally (as I did) or add it externally.
Have fun.
73,
... Martin VE3OAT

As seen by these answers so far, there are lots of options. If, like me, you'd prefer to go the kit or pre-built route, there are options from cheap and simple to expensive and more complex.

I personally built the Hi-Per-Mite from Four State QRP: http://www.4sqrp.com/hipermite.php. It's a 200 Hz (fixed bandwidth) CW filter kit that costs $25 delivered and is powered by a 9 volt battery. It can all fit in an Altoids tin or other similarly sized enclosure. I had ordered some jacks and small enclosures (about the size of a deck of cards) for another project and used them for this, too (see photo -- Altoids tin is for size reference -- email me for parts sources, if interested). As Jerry Gaffke indicated, it's easy to use because it connects between the uBITX and your headphones. And, since it's an external device, it can be used with any radio that has an audio out jack. I've used it with my uBITX and my Xiegu G90 and it works well. Once I add an on/of switch, it'll be complete.



If you want a wider (but still fixed) bandwidth, QRP Guys have a CW filter kit with a 600 Hz bandwidth for only $20: https://qrpguys.com/qrpguys-active-600hz-audio-filter. This kit even comes with on/off and in/out switches and two audio jacks. All you need to supply is an enclosure, if you want one, and a 9 volt battery.

SOTABEAMS has a slightly more expensive DSP audio filter kit (also available pre-built), but it is more flexible because it comes with selectable filter bandwidths: https://www.sotabeams.co.uk/dsp-audio-filter-units-ready-to-use/. Prices start around $60 if bought outside the EU (EU customers pay a 20% VAT).

SOTABEAMS also has their new Wolfwave audio processor, but that is probably overkill and starts at around $300 if bought outside the EU: https://www.sotabeams.co.uk/wolfwave-advanced-audio-processor/.

Well i don't know about that.  Its good no doubt but you can do just as well with a sotabeam filter or customize one by purchasing the audio shield from PJRC and a teensy and make just about any kind of filter you want at a much lower cost. Worst case you can just use the filter part of the code in the JackAl.

--

…_. _._

As seen by these answers so far, there are lots of options. If, like me, you'd prefer to go the kit or pre-built route, there are options from cheap and simple to expensive and more complex.

I personally built the Hi-Per-Mite from Four State QRP: http://www.4sqrp.com/hipermite.php. It's a 200 Hz (fixed bandwidth) CW filter kit that costs $25 delivered and is powered by a 9 volt battery. It can all fit in an Altoids tin or other similarly sized enclosure. I had ordered some jacks and small enclosures (about the size of a deck of cards) for another project and used them for this, too (see photo -- Altoids tin is for size reference -- email me for parts sources, if interested). As Jerry Gaffke indicated, it's easy to use because it connects between the uBITX and your headphones. And, since it's an external device, it can be used with any radio that has an audio out jack. I've used it with my uBITX and my Xiegu G90 and it works well. Once I add an on/of switch, it'll be complete.



If you want a wider (but still fixed) bandwidth, QRP Guys have a CW filter kit with a 600 Hz bandwidth for only $20: https://qrpguys.com/qrpguys-active-600hz-audio-filter. This kit even comes with on/off and in/out switches and two audio jacks. All you need to supply is an enclosure, if you want one, and a 9 volt battery.

SOTABEAMS has a slightly more expensive DSP audio filter kit (also available pre-built), but it is more flexible because it comes with selectable filter bandwidths: https://www.sotabeams.co.uk/dsp-audio-filter-units-ready-to-use/. Prices start around $60 if bought outside the EU (EU customers pay a 20% VAT).

SOTABEAMS also has their new Wolfwave audio processor, but that is probably overkill and starts at around $300 if bought outside the EU: https://www.sotabeams.co.uk/wolfwave-advanced-audio-processor/.

The MAX7400 switched capacitor audio low pass filter is an interesting part.
Simple to use, and only draws a couple ma.
Has an internal oscillator that Andy is tuning with the 1n4148 used as a varicap diode,
but could drive the clock pin from a Nano counter-timer at 100 times the desired corner frequency.
That way you could tune it in firmware.

However, this is a low pass filter, not a band pass filter like some of the alternatives are.
So it will not attenuate frequencies that are below the desired signal.

Jerry, KE7ER
 

The MAX7400 is a low pass filter, however if the uBitx crystal filter is doing 
its job there should already be a sharp lower cutoff frequency of around 300 Hz.
So the total system is effectively a good sharp bandpass filter.
That lower cutoff frequency can be adjusted by moving the BFO.

Jerry, KE7ER

The MAX7410 can also be used as a notch filter.  I usually need one of these about as often as I do a peak filter. I am going to order a couple and experiment.  They are about $6 each at Digikey.

https://www.maximintegrated.com/en/design/technical-documents/app-notes/4/431.html

Jim KH6SKY