Topics

Narrow filter for CW #ubitxcw

_Dave_ K0MBT
 

Hello
I am teaching myself CW and find that the receive filters are too wide even when in cwl or cwu. Many times I hear 3 or 4 signals and it becomes confusing to my new CW ears and older brain.

Has any on designed an IF filter that would be suitable for cw?

I have a v3 and v4 uBITX's Running kd8cec firmware and Nextion displays.

Thanks
Dave
k0mbt

Curt
 

Dave

Funny how many of us could do cw with 3 khz or wider filtering decades ago, when a narrow filter cost maybe as much as our receiver.

The design of the ubitx with its bidirectional amplifiers does not easily allow adding a second xtal filter for cw nor IF agc. So think audio filtering.

I use a NESCAF audio filter that features adjustable bandwidth for cw and ssb. And it adds a lm386 audio amplifier output. Mine is external,  but I plan to integrate it. 4state qrp has a narrow cw filter. Kc9on has the CALF audio filter, a bit large but nice audio filter to use with several different rigs.

A cw filter much more important than agc. Being able to easily switch back to ssb is desirable.

Curt

John Seboldt K0JD
 

I tend to like a wide bandwidth for my CW if the interference isn't ghastly. An extra signal peeping along up there at 2 kHz or so doesn't bother me unless it's HUUUGE. I set myself the challenge of doing a CWT contest with the uBITX - stock filtering - and it was do-able - sometimes moving the headphones around helped me discern the wanted signal a little better.

Of course there's a time and place for a narrow filter - really weak stuff or a really busy contest.

I might borrow the one from the QCX - quite nice.

John K0JD

On 8/12/2019 10:29, Curt via Groups.Io wrote:
Dave

Funny how many of us could do cw with 3 khz or wider filtering decades ago, when a narrow filter cost maybe as much as our receiver.

The design of the ubitx with its bidirectional amplifiers does not easily allow adding a second xtal filter for cw nor IF agc. So think audio filtering.

I use a NESCAF audio filter that features adjustable bandwidth for cw and ssb. And it adds a lm386 audio amplifier output. Mine is external,  but I plan to integrate it. 4state qrp has a narrow cw filter. Kc9on has the CALF audio filter, a bit large but nice audio filter to use with several different rigs.

A cw filter much more important than agc. Being able to easily switch back to ssb is desirable.

Curt

Richard Spohn
 

See if the Wolfwave audio DSP filter will help. DXEngineering. - Rich WB2GXM

On 8/12/19, _Dave_ K0MBT <davesters@...> wrote:
Hello
I am teaching myself CW and find that the receive filters are too wide even
when in cwl or cwu. Many times I hear 3 or 4 signals and it becomes
confusing to my new CW ears and older brain.

Has any on designed an IF filter that would be suitable for cw?

I have a v3 and v4 uBITX's Running kd8cec firmware and Nextion displays.

Thanks
Dave
k0mbt



Jim
 

If I am remembering correctly my old SP600JX would go down to 200 cycles. You could pull a needle from a haystack with that one. It would sound somewhat hollow. Also remember the astronomical prices of the Collins filters for the KWM series! You could probably buy 3 BITx..for what they cost.

Ashhar Farhan
 

The ubitx has an option for narrow band filter. There are pins to install it. The way it works is a bit of a hack :
1. The CW filter is at a different frequency. Let's imagine it is at 4.915 MHz. It is installed parallel to the 11.059 MHz SSB filter.
2. When choosing CW filter, you have to switch the second conversion oscillator from 56.059 Mhz (45 + 11.059) to 49.915 Mhz (45 +4.915). Shift the BFO to 4.914500 (According to your taste of CW tone).
Apart from designing the crystal filter, this hack is mostly about software changes.

73, f


On Tue 13 Aug, 2019, 4:46 AM Jim, <Jscook@...> wrote:
If I am remembering correctly my old SP600JX would go down to 200 cycles. You could pull a needle from a haystack with that one. It would sound somewhat hollow. Also remember the astronomical prices of the Collins filters for the KWM series! You could probably buy 3 BITx..for what they cost.



Evan Hand
 

If you have the KD8CEC software and the Nextion display, using the IF shift and the sideband adjustment, I found that you can shift the received signal to be limited on one edge of the 2.5 khz filter effectively reducing the received bandwidth.  The two controls were designed to filter out unwanted signals.  Worth a try IF you have the Nextion display mod.  

FWIW
73
Evan
AC9TU

Jerry Gaffke
 

Looks like PA1FOX has successfully added a second crystal filter for CW:
    https://groups.io/g/BITX20/message/48555
Perhaps Farhan has done this as well.

A perhaps easier hack is to simply add an audio filter for CW, as many here have done.
Some operators will prefer the narrow crystal filter for CW, as this avoids overloading
the receiver audio pre-amp when a strong nearby signal is present.

Evan's hack:  https://groups.io/g/BITX20/message/71042
is well worth trying.  I have not tried the KD8CEC firmware, but should be possible
to implement this with a firmware change only, no Nextion display, no hardware mods.

Jerry, KE7ER


On Mon, Aug 12, 2019 at 06:10 PM, Ashhar Farhan wrote:
The ubitx has an option for narrow band filter. There are pins to install it. The way it works is a bit of a hack :
1. The CW filter is at a different frequency. Let's imagine it is at 4.915 MHz. It is installed parallel to the 11.059 MHz SSB filter.
2. When choosing CW filter, you have to switch the second conversion oscillator from 56.059 Mhz (45 + 11.059) to 49.915 Mhz (45 +4.915). Shift the BFO to 4.914500 (According to your taste of CW tone).
Apart from designing the crystal filter, this hack is mostly about software changes.
 

Tom, wb6b
 

Hi,

Are there any comparisons that would indicate if a narrower bandwidth crystal filter verses an audio bandpass filter perform better? In some ways the audio filter is just another filter in the IF chain, and the current crystal filter becomes a second roofing filter.

Also, it would seem with DSP technology, filters, noise reduction and such would be possible in ways that were never possible with tried and true crystal filters and analog techniques. Have DSP audio processors delivered on these possibilities?

My old school HF transceiver has a narrow CW crystal filter and it seems to work well, but for my UBitx maybe something new school would be more practical.

In a field day situation if a high power station was near by in distance and frequency it could help. But if the radio was good enough to not overload, in that case, is it due to the crystal filter or simply the design of the receiver can handle a high dynamic range?

Are there any good articles or comparisons of one over the other? I'd been thinking of adding a audio bandpass filter to my UBitx, but sounds like it is not difficult to add a narrower crystal filter if done in "parallel" as suggested here. The difference in IF frequency seems like it would just be a software change, unlike radios of old. 

Tom, wb6b

Ashhar Farhan
 

If close in signals are not a worry then certainly a digital filter is indicated. The one large advantage of a digital filter is that there is no phase distortion. Thus ringing is minimum. But you need a very good 24 bit codec.
- f

On Tue 13 Aug, 2019, 12:30 PM Tom, wb6b, <wb6b@...> wrote:
Hi,

Are there any comparisons that would indicate if a narrower bandwidth crystal filter verses an audio bandpass filter perform better? In some ways the audio filter is just another filter in the IF chain, and the current crystal filter becomes a second roofing filter.

Also, it would seem with DSP technology, filters, noise reduction and such would be possible in ways that were never possible with tried and true crystal filters and analog techniques. Have DSP audio processors delivered on these possibilities?

My old school HF transceiver has a narrow CW crystal filter and it seems to work well, but for my UBitx maybe something new school would be more practical.

In a field day situation if a high power station was near by in distance and frequency it could help. But if the radio was good enough to not overload, in that case, is it due to the crystal filter or simply the design of the receiver can handle a high dynamic range?

Are there any good articles or comparisons of one over the other? I'd been thinking of adding a audio bandpass filter to my UBitx, but sounds like it is not difficult to add a narrower crystal filter if done in "parallel" as suggested here. The difference in IF frequency seems like it would just be a software change, unlike radios of old. 

Tom, wb6b

Dennis Zabawa
 

Here is another alternative for the audio side: Variable Audio Filter

Jack Purdum
 

HI Tom:

Inexpensive DSP is incorporated into the JackAl board. This shot shows the "canned" SSB filters (1500, 1800, 2200, 3000), but the JackAl also provides "canned" CW filters, too (150, 300, 400 600Hz, and "Cust"):

Inline image


The "Cust" choice is for a filter where you get to set the "skirts" to whatever best suits your needs. Al (AC8GY) and I made the JackAl project Open Source, and  you can get the assembly manuals, code, and schematics from:



QRP Guys sell the JackAl board, which has all on-board SMD parts mounted.

Jack, W8TEE



On Tuesday, August 13, 2019, 3:00:12 AM EDT, Tom, wb6b <wb6b@...> wrote:


Hi,

Are there any comparisons that would indicate if a narrower bandwidth crystal filter verses an audio bandpass filter perform better? In some ways the audio filter is just another filter in the IF chain, and the current crystal filter becomes a second roofing filter.

Also, it would seem with DSP technology, filters, noise reduction and such would be possible in ways that were never possible with tried and true crystal filters and analog techniques. Have DSP audio processors delivered on these possibilities?

My old school HF transceiver has a narrow CW crystal filter and it seems to work well, but for my UBitx maybe something new school would be more practical.

In a field day situation if a high power station was near by in distance and frequency it could help. But if the radio was good enough to not overload, in that case, is it due to the crystal filter or simply the design of the receiver can handle a high dynamic range?

Are there any good articles or comparisons of one over the other? I'd been thinking of adding a audio bandpass filter to my UBitx, but sounds like it is not difficult to add a narrower crystal filter if done in "parallel" as suggested here. The difference in IF frequency seems like it would just be a software change, unlike radios of old. 

Tom, wb6b

Jack Purdum
 

On Tuesday, August 13, 2019, 8:32:49 AM EDT, Dennis Zabawa <kg4rul@...> wrote:


Here is another alternative for the audio side: Variable Audio Filter

KD8CGH
 

I'm using the tiny SOTABEAMS CW filter board. It is switched so that I can have it out for SSB and in for CW. It has two widths: 300 Hz and 1000 Hz. As a bonus it will also light an LED as a tuning indicator for those of us that are pretty tone deaf. Not bad for $30 + $5.79 shipping to USA.

https://www.sotabeams.co.uk/dual-bandwidth-filter-modules-ssb-cw/

Ashhar Farhan
 

The jackal board offers a very good choice of filters as well as many excellent features.
It provides a fantastic value at such a low price point.
- f

On Tue 13 Aug, 2019, 7:18 PM KD8CGH, <rkayakr@...> wrote:
I'm using the tiny SOTABEAMS CW filter board. It is switched so that I can have it out for SSB and in for CW. It has two widths: 300 Hz and 1000 Hz. As a bonus it will also light an LED as a tuning indicator for those of us that are pretty tone deaf. Not bad for $30 + $5.79 shipping to USA.

https://www.sotabeams.co.uk/dual-bandwidth-filter-modules-ssb-cw/

MadRadioModder
 

Yes I use my own coded version of this thing and it works very well as long as the IF is not over-loading…

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Dennis Zabawa
Sent: Tuesday, August 13, 2019 7:33 AM
To: BITX20@groups.io
Subject: Re: [BITX20] Narrow filter for CW #ubitxcw

 

Here is another alternative for the audio side: Variable Audio Filter


Virus-free. www.avg.com

--

…_. _._

MadRadioModder
 

I even coded a small display to show the passband of my digital filter… it has two encoders… used identically like the Elecraft K3 filter… move either the upper and lower cut-off point, or press the button, and move the center frequency and filter width (LEDs indicate mode).  Four stored adjustable filters (CW, SSB, RTTY, AM).  Uses a Teensy 3.6 and the audio board (like the JackAl).  See attached.

 

 

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of MadRadioModder via Groups.Io
Sent: Tuesday, August 13, 2019 9:42 AM
To: BITX20@groups.io
Subject: Re: [BITX20] Narrow filter for CW #ubitxcw

 

Yes I use my own coded version of this thing and it works very well as long as the IF is not over-loading…

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Dennis Zabawa
Sent: Tuesday, August 13, 2019 7:33 AM
To: BITX20@groups.io
Subject: Re: [BITX20] Narrow filter for CW #ubitxcw

 

Here is another alternative for the audio side: Variable Audio Filter

 

Virus-free. www.avg.com


--

…_. _._


--

…_. _._

_Dave_ K0MBT
 

Ash
Does this option work on the V3 or V4 radios as well. Now to source more data on this option.

Evan
Yes as I mentioned I have the nextion display on most of my ubitx radios. I noticed that the IF shift when slid from one side to the other can make certain tones disappear and reappear I guess I should move it to one side or the other and see if I can use it to isolate. I assume it is a one way shift on the receive side only.

Thanks to all that wrote thoughtful replies.

On Mon, Aug 12, 2019 at 08:10 PM, Ashhar Farhan wrote:


The ubitx has an option for narrow band filter. There are pins to install it.
The way it works is a bit of a hack :
1. The CW filter is at a different frequency. Let's imagine it is at 4.915
MHz. It is installed parallel to the 11.059 MHz SSB filter.
2. When choosing CW filter, you have to switch the second conversion
oscillator from 56.059 Mhz (45 + 11.059) to 49.915 Mhz (45 +4.915). Shift the
BFO to 4.914500 (According to your taste of CW tone).
Apart from designing the crystal filter, this hack is mostly about software
changes.

Curt
 

Dave

I sense we have thrown lots of choices at you.  Except for playing with IF shift, implementing an audio filter is easiest - with many low cost choices around.  Note in most respects the design architecture is very similar across v3, v4 and v5.  v5 was a larger change with a different IF selection for the SSB crystal filter. 

Many of us have rigs with 4915 kHz xtal filters made from cheap xtals.  Sounds like it could be installed in parallel with the 12 MHz filter without needing relays -- I should have thought of that - but we need a rig control to command the ubitx to 'Receive CW' to change the oscillator functions as Asher describes. 

Except in a major contest maybe, I find the audio filter is entirely sufficient with the way ubitx receive gain is distributed.  You might find CW transmit behavior a bit strange but it works fine once you are used to it. 

Curt

iz oos
 

I guess an audio active filter 200hz wide like the Hipermite by 4SQRP might suffice.


Il 14/ago/2019 19:59, "Curt via Groups.Io" <wb8yyy=yahoo.com@groups.io> ha scritto:
Dave

I sense we have thrown lots of choices at you.  Except for playing with IF shift, implementing an audio filter is easiest - with many low cost choices around.  Note in most respects the design architecture is very similar across v3, v4 and v5.  v5 was a larger change with a different IF selection for the SSB crystal filter. 

Many of us have rigs with 4915 kHz xtal filters made from cheap xtals.  Sounds like it could be installed in parallel with the 12 MHz filter without needing relays -- I should have thought of that - but we need a rig control to command the ubitx to 'Receive CW' to change the oscillator functions as Asher describes. 

Except in a major contest maybe, I find the audio filter is entirely sufficient with the way ubitx receive gain is distributed.  You might find CW transmit behavior a bit strange but it works fine once you are used to it. 

Curt