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ubitx cw listening width modification

Brien Pepperdine
 

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In my quick read of the circuit description it says the same width for listening to SSB and CW, but that there is no reason the Arduino code could not be altered to provide a 500 hz bandwidth.

That would be absolutely required for me... I realize this is a fairly reasonably priced kit for what ALL it does, but I am very used to using 600 hz for general tuning around and? narrower at around 500 or 400 for QSO operation... if not narrow sometimes in regard to band congestion... so am interested in what the CW ops might say on this topic re. operation.

Brien

VE3VAW

Toronto ON Canada

---------- Original Message ----------
From: Doug W <KD9CYF@...>
Date: December 9, 2017 at 5:28 PM

Thanks for all your work Ashhar.? Just ordered mine.

I don't know if it aired outside of the US but there is an old commercial for Lay's potato chips (crisps) that comes to mind...


?
Gordon Gibby
 

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Hi Brien --? ?


The filter width is set by a crystal filter.? ?The Raduino? (Arduino-controlled VFO)?does not produce the audio signal, so I don't think you would be able to introduce an audio digital filter within it.? ?


You could add an audio filter to the output (digital or otherwise)? or you could electrically alter the configuration of the crystal filter that sets the bandwidth.? ?My BitX40's only had 4 cystals (quite fewer than the uBitx) and appeared to me to have a narrower bandwidth.? ?It is possible that you could use capacitors or wiring to bypass (or "pull" with capacitors/inductors) some of the cyrstals in the filter to make it narrower.? ??


That's the limit of my knowledge, perhaps others will offer better solutions.? ?


Thanks!

Gordon?



From: [email protected] <[email protected]> on behalf of Brien Pepperdine <brianpepperdine@...>
Sent: Saturday, December 9, 2017 6:02 PM
To: [email protected]
Subject: Re: [BITX20] ubitx cw listening width modification
?

In my quick read of the circuit description it says the same width for listening to SSB and CW, but that there is no reason the Arduino code could not be altered to provide a 500 hz bandwidth.

That would be absolutely required for me... I realize this is a fairly reasonably priced kit for what ALL it does, but I am very used to using 600 hz for general tuning around and? narrower at around 500 or 400 for QSO operation... if not narrow sometimes in regard to band congestion... so am interested in what the CW ops might say on this topic re. operation.

Brien

VE3VAW

Toronto ON Canada

---------- Original Message ----------
From: Doug W <KD9CYF@...>
Date: December 9, 2017 at 5:28 PM

Thanks for all your work Ashhar.? Just ordered mine.

I don't know if it aired outside of the US but there is an old commercial for Lay's potato chips (crisps) that comes to mind...


?
 

The ubitx is quitr hackable that way. Here is a hack.
You take the signal off from both ends of the crystal filter and add a parallel one, say at 1.8432 mhz. This will provide a very narrow cw filter. Now, all you have to do to switch the filter is change your second if to 45 mhz + 1.8432 mhz. viola! narrow band cw


On 17 Dec 2017 8:16 am, "Gordon Gibby" <ggibby@...> wrote:

Hi Brien --? ?


The filter width is set by a crystal filter.? ?The Raduino? (Arduino-controlled VFO)?does not produce the audio signal, so I don't think you would be able to introduce an audio digital filter within it.? ?


You could add an audio filter to the output (digital or otherwise)? or you could electrically alter the configuration of the crystal filter that sets the bandwidth.? ?My BitX40's only had 4 cystals (quite fewer than the uBitx) and appeared to me to have a narrower bandwidth.? ?It is possible that you could use capacitors or wiring to bypass (or "pull" with capacitors/inductors) some of the cyrstals in the filter to make it narrower.? ??


That's the limit of my knowledge, perhaps others will offer better solutions.? ?


Thanks!

Gordon?



From: [email protected] <[email protected]> on behalf of Brien Pepperdine <brianpepperdine@...>
Sent: Saturday, December 9, 2017 6:02 PM
To: [email protected]
Subject: Re: [BITX20] ubitx cw listening width modification
?

In my quick read of the circuit description it says the same width for listening to SSB and CW, but that there is no reason the Arduino code could not be altered to provide a 500 hz bandwidth.

That would be absolutely required for me... I realize this is a fairly reasonably priced kit for what ALL it does, but I am very used to using 600 hz for general tuning around and? narrower at around 500 or 400 for QSO operation... if not narrow sometimes in regard to band congestion... so am interested in what the CW ops might say on this topic re. operation.

Brien

VE3VAW

Toronto ON Canada

---------- Original Message ----------
From: Doug W <KD9CYF@...>
Date: December 9, 2017 at 5:28 PM

Thanks for all your work Ashhar.? Just ordered mine.

I don't know if it aired outside of the US but there is an old commercial for Lay's potato chips (crisps) that comes to mind...


?
 

I plan to add an inexpensive audio filter on the output.
Note also the the frequency you see in CW with the uBitx will differ from the frequency reported by commercial rigs that take into account a side tone offset in CW mode.
 

Take a look at the NESCAF. I have 3 of them, one in a stand alone case with a zero beat kit, one in my Bitx40 and one waiting for a ubitx hihi. I just love them for CW and with the Bitx40 it can help change the pitch of a SSB weak signal and I can pick it out better.

?

NEQRP is now selling them again

?

73

? David
 

Brien :?

I think that the IF filter bandwidth in the uBITX is fixed by hardware.

The solution for CW filtering that I used with my BITX40,?and which I also intend to apply to my uBITX, is to install a SotaBeams Laserbeam DSP audio filter module in the audio chain before the audio amplifier (at the AF Gain POT). ?These little pre-assembled?modules work better than any analog audio filter I have ever used, only consume 30ma and are?pretty much brick-wall filters. I put the General purpose 2.4Khz SSB / 300 Hz CW module into my?BITX40 with a three pole switch so I can also bypass the filter as well as selecting 2.4 Khz / 300 Hz. ?Cost is about $US30.?

For my uBITX (which I hope will ship soon ;-) ) I have ordered another General Purpose SOTABEAMs filter but this time the 1Khz / 300 Hz CW filter and I will also use the bypass option for SSB.

SotaBeams has a few different modules available, including one with variable bandwidth that
might work better for some folks.?

Here is a link :?

https://www.sotabeams.co.uk/audio-products/

Cheers

Michael VE3WMB?

P.S. One added feature of this audio filter that is great for CW, is the installation of
the optional signal LED. ?If installed it will light when a CW signal is near the middle of the filter passband, giving?you a bonus tuning aid for CW stations.?
 

First my apologies for perhaps asking question that answer is commonly known. Also please note that I have zero experience re either the Bitx units OR Arduino based rigs...

So, I can understand that by changing the IF frequency another filter can be used based on moving signal to the appropriate range. In this case a filter made by using commonly available?1.8432 Mhz crystals. And this in turn will require some change in code so that when appropriate request received (h/w switch or menu item?) to change bandwidth. As an aside, what is the original purpose of crystals manufactured for 1.8? Surly not 'top band' as there seems to be lots available in the market place! Perhaps some T.V. circuitry? ?Back to my question...

What puzzles me is how the 1.8 filter will have a narrower bandwidth? Obvious answer is that will be 'by design' so guess that's another topic I need to go and research but before doing so wanted to make sure that the correct answer has nothing to do with the design of the Bitx. (remember I currently have NO insight or experience with this design)

As always many thanks in advance and remember to KEEPSMILING!?
 

By design, in part.? The caps and termination impedance play a part.
But also, the bandwidth of a crystal filter should be proportional to the frequency at which it is used.
So a crystal filter at 2mhz "starts out" being 6 times narrower than a crystal filter at 12mhz when using the same design parameters.


On Wed, Dec 20, 2017 at 04:19 am, Nigel wrote:
What puzzles me is how the 1.8 filter will have a narrower bandwidth? Obvious answer is that will be 'by design'
 

On Wed, Dec 20, 2017 at 6:19 AM, Nigel <zs6rn@...> wrote:
What puzzles me is how the 1.8 filter will have a narrower bandwidth? Obvious answer is that will be 'by design' so guess that's another topic I need to go and research but before doing so wanted to make sure that the correct answer has nothing to do with the design of the Bitx. (remember I currently have NO insight or experience with this design)

Designing and building a crystal filter with a particular bandwidth from a collection of crystals nominally of the same frequency is an art in itself. For best performance, the individual crystals need to be characterized for their resonant frequency and self-capacitances. Then those data can be input to various software to design the actual filter. Software options include LADPAC from W7ZOI (no longer available) or Dishal. (Are there other more modern software packages that we could be suggesting here?) W7ZOI's book Experimental Methods in Radio Frequency Design (EMRFD) has a fairly good introduction to the process. References on may also help you get started.

Parenthetically, the difficulty in building narrow RF filters provides some of the impetus for the industry's move to SDR or DSP audio filtering (such as these ). Part of Farhan's genius (handed down from W7ZOI) is in tackling these difficult RF design problems to provide us with such a capable analog HF radio.

-Neil N0FN
 

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1.8432 crystals are one of several that are used for baud rate generation. ?They allow for dividing down exactly to many common baud rates 9600 and 57600 among others. ?Microcontrollers with built in dividers for serial ports can use any frequency crystal but using say a 16MHz crystal you can’t get exactly 9600 baud. ?Typically it’s well within serial data tolerances at 9600. ?But if you want to use 57,600 or 115,200 it’s going to be iffy or worse. ?I commonly use 18,432,000 for a MCU clock. ?That allows me to get exact baud rates and it can also divide down to 1KHz for timing purposes.


Clark Martin
KK6ISP

On Dec 20, 2017, at 4:19 AM, Nigel <zs6rn@...> wrote:

So, I can understand that by changing the IF frequency another filter can be used based on moving signal to the appropriate range. In this case a filter made by using commonly available?1.8432 Mhz crystals. And this in turn will require some change in code so that when appropriate request received (h/w switch or menu item?) to change bandwidth. As an aside, what is the original purpose of crystals manufactured for 1.8? Surly not 'top band' as there seems to be lots available in the market place! Perhaps some T.V. circuitry? ?Back to my question...
 

I second David's NESCAF comments. I've used mine to great effect on several radios...including my K-1 and a 3 tube regen set (!) and it's a star for CW work.
Happy to see the NE QRP group decided to bring it back.
 

I have the Sotabeam cw DSP filter as a peripheral, using it on another rig, and it is good. ?I tried it on the uBitx and it is a definite improvement. ?However, I'm also going to try my old favorite, the Hi-Per-Mite SCAF from Four Square QRP Group (). I have one with for each of my rigs and love it. ?The excellent QCX transceiver uses it as well.
Howard K4LXY

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