Topics

CW Filter

Reg
 

Hi,
I finished my uBitX V5 sometime ago and it works well. I am impressed with it, all I needed was a good CW filter.
Having obtained and fitted one of these I am amazed at just how good it is.

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

I bought the dual bandwidth CW version and fitted into the line to the input of the volume control. I double pole, double throw switch allows the filter to be by passed or put into line where it is then in it's wider setting.. A separate, simple on off switch, then selects the narrow filter mode.

Performance of the filter is very good and when in it's narrowest settings a signal is peaked and just pops right out in the clear. A brilliant addition to the uBitX.

Reg             G4NFR 

laurent.bury@...
 

Hi Reg,

sounds great, as the uBitx lacks a good CW filter (the provided one is set for SSB, that is much too wide when chasing for DX stations listening up...about 1Khz, right in the audio response :( ).

As you talked about the volume control, I wondered if the CW filter was compliant with any audio AGC one can have already add, that is connected  to the volume pot ?

73s
--
Laurent F5FIE.

Reg
 

Hi Laurent,
The Sotabeams filter is very good and saves messing about making one. I would think that it should be O.K when used in line with an AGC control. But that's a guess as I haven't got any AGC control. I might look at the simple AGC setup designed by Peter Parker VK3YE

https://www.youtube.com/watch?v=GdpOkjETtw8

But that's a future  project.

Reg     G4NFR

Reg
 

A better video for the VK3YE AGC is here and it's in two parts.


Reg       G4NFR

Bob Benedict, KD8CGH
 

I also use the Sotabeams filter. As a bonus for us tone deaf operators it includes a CW tune aid that lights an led when well tuned to a signal.

laurent.bury@...
 

Hi Reg,

tnx for your reply; I saw this LED AGC, running at audio stage, before choosing this one, running at RF stage:
https://shop.kit-projects.com/index.php?route=product/product&product_id=101

I'm quite confused as this last AGC has a wire connected to the yellow wire of the volume pot:
I'm not sure I can insert the Sotabeams filter in line between the tip of the pot and the wire coming from the AGC PCB ?

Did you insert yours this way ?

73, Laurent F5FIE.

Reg
 

Hi Laurent,

I inserted the Sotabeams filter into the yellow wire leading to the volume control.
I did use a switch to bypass the filter or put it inline.
I will draw a sketch of the wiring, scan it and put it on here tomorrow (Sunday).
My original sketch is not that pretty. It took me a while to work out the wiring to use a double pole, two way switch.
Perhaps it will save someone from working it out again.

Reg               G4NFR

Bob Clarke
 

Has anyone looked at designing a crystal filter for CW, any number of poles? I like the notion of using adjustable digital filters but believe based on my industry experience that any ADC should preceded by decent analog filtering to prevent overload by IMD. 

Thanks! 

Bob, N1RC

Jerry Gaffke
 

Yup.
Here's an old thread on adding a separate CW crystal filter to the uBitx:
    https://groups.io/g/BITX20/topic/32840565

Jerry, KE7ER


On Sat, Mar 14, 2020 at 07:40 PM, Bob Clarke wrote:
Has anyone looked at designing a crystal filter for CW, any number of poles? I like the notion of using adjustable digital filters but believe based on my industry experience that any ADC should preceded by decent analog filtering to prevent overload by IMD. 

Thanks! 

Bob, N1RC

Scott McDonald
 

Bob, I built a quick simple 4 pole cw filter using matched crystals (Only 1.50 each) from W8DIZ for a UBITX Receiver based on v3, and I think he is stocking 12 MHz matched crystals now.

Only issue was getting the cw BFO where I needed it but using KD8CEC software made that easy enough.

73 Scott ka9p

Make something good happen!

On Mar 14, 2020, at 9:41 PM, Bob Clarke <bclarke@...> wrote:

Has anyone looked at designing a crystal filter for CW, any number of poles? I like the notion of using adjustable digital filters but believe based on my industry experience that any ADC should preceded by decent analog filtering to prevent overload by IMD. 

Thanks! 

Bob, N1RC

Scott McDonald
 



Bob, that will give you an idea of what I got with a quick and dirty 4 pole, not to die for but a big improvement over the ssb filter.

73 Scott


On Mar 14, 2020, at 10:38 PM, Scott McDonald via Groups.Io <ka9p@...> wrote:

Bob, I built a quick simple 4 pole cw filter using matched crystals (Only 1.50 each) from W8DIZ for a UBITX Receiver based on v3, and I think he is stocking 12 MHz matched crystals now.

Only issue was getting the cw BFO where I needed it but using KD8CEC software made that easy enough.

73 Scott ka9p

Make something good happen!

On Mar 14, 2020, at 9:41 PM, Bob Clarke <bclarke@...> wrote:

Has anyone looked at designing a crystal filter for CW, any number of poles? I like the notion of using adjustable digital filters but believe based on my industry experience that any ADC should preceded by decent analog filtering to prevent overload by IMD. 

Thanks! 

Bob, N1RC

MadRadioModder
 

Interesting note here... if you use series varactor diodes to ground on the inner caps (that go to ground) and put variable voltage on the junction...you instantly have a variable pass-band control.  I believe that was done in the Elecraft K2 as well.  Check the circuit. 


MRM

 


On Mar 14, 2020, at 11:58 PM, Scott McDonald via Groups.Io <ka9p@...> wrote:


<image0.jpeg>


Bob, that will give you an idea of what I got with a quick and dirty 4 pole, not to die for but a big improvement over the ssb filter.

73 Scott


On Mar 14, 2020, at 10:38 PM, Scott McDonald via Groups.Io <ka9p@...> wrote:

Bob, I built a quick simple 4 pole cw filter using matched crystals (Only 1.50 each) from W8DIZ for a UBITX Receiver based on v3, and I think he is stocking 12 MHz matched crystals now.

Only issue was getting the cw BFO where I needed it but using KD8CEC software made that easy enough.

73 Scott ka9p

Make something good happen!

On Mar 14, 2020, at 9:41 PM, Bob Clarke <bclarke@...> wrote:

Has anyone looked at designing a crystal filter for CW, any number of poles? I like the notion of using adjustable digital filters but believe based on my industry experience that any ADC should preceded by decent analog filtering to prevent overload by IMD. 

Thanks! 

Bob, N1RC

--

…_. _._

Reg
 

Hi Laurent,
As promised the wiring I used to fit a Sotabeams CW filter into the uBitX, mine is a Version 5 board.

J1 is the connection on the board and a yellow wire comes from that and is soldered to the input of the volume control.
J2 has an orange wire that goes from the wiper of the volume control back to the board alongside J1 and the yellow wire. The third terminal on the volume control goes to ground connection.

With the switch up the yellow wire from J1 on the board goes to 2 on the switch and 1 on the switch takes it to the input of the volume control - so the filter is bypassed.

When the switch is down then 2 on the switch is connected to 3 and the signal is then taken to the input of the filter. The signal passes through the filter and returns to 5 on the switch which is also connected to 6 and the filtered signal is returned to the input of the volume control.

The audio level is controlled by the volume control whether the filter is by-passed or inline. When the filter is switched in it is in wide CW mode. A second switch is needed to switch a terminal on the filter to ground and that gives the narrow CW mode but I have left that off the drawing.

I don't see why you can't fit the AGC into the yellow wire leading to the input of the volume control and then put the filter between it and the input. I don't have AGC (yet) but this wiring works perfectly for me.

Hope that helps,
Reg      G4NFR 

laurent.bury@...
 

Hello Reg,

thank you so much for the wiring sketch, it will for sure be a great help !


I think you are right: I should be able to insert the filter between the AGC yellow wire and its final destination to the volume pot...

I just need to order the filter now, but will wait for the end of the virus crisis as parcel's transportation services will be off or so for a while.

I'll let you know ;)

Best 73.

--
Laurent F5FIE.

Reg
 

Hi Laurent,
Good luck with the project and let us know how you get on when you can get the parts.
The corona virus is causing serious disruption already.

Reg   G4NFR

laurent.bury@...
 

Hi Reg,

I just finished today to fit the Sotabeams in my uBitx case.



I used the genuine audio output (yellow wire) of the uBitx, to feed the Sotabeams filter (audio In), connected along with the "V" output of my AGC (https://shop.kit-projects.com/index.php?route=product/product&product_id=101), and the audio output of the filter to the High side of the volume pot.

No RF troubles in the audio, and the filter is VERY efficient in CW narrow mode :)

73s F5FIE.


--
Laurent F5FIE.

R. Tyson
 

Hi Laurent,

Well done and the filter makes a dramatic difference to the uBitX.

I have been really impressed by mine. Another thing I found - the uBitX is very stable.
I had the filter switched to it's narrowest position and was listening to a CW station while messing about with something on the bench. The signal stayed exactly the same for around 10 to 15 minutes with no sign of frequency drift. That also proved the other guy was stable as well.

73's

Reg            G4NFR