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Help with CW filter insertion
#ubitx-v6
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Before I butcher the wrong trace, can anyone confirm that I've identified the correct trace to cut to insert a CW filter ahead of the headphone jack on my V6?? See attached photo.? Not sure the photo is coming through.? I'm considering cutting the outermost trace on the front of the board to the right of the headphone jack.? Thanks.? /John? W7SWB
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John
Is this an audio cw filter?? Does it include an amplifier??? Mine is a Nescaf. I placed it within the wires between the board and the audio outputs, speaker and headphone. I adjusted the audio filter board for roughly equal 0 dB gain.? For a crystal IF filter some ubitx versions have mounting pads. I may see those to the left of the crystals.? Confirm anything with your ohmmeter.? Curt |
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Curt,
I believe that John has a v6 board with the jacks and controls mounted on it.? He will need to cut a trace to do the same thing as a v5, or an earlier mod would allow. John, I suggest scraping a small section of solder mask off the trace and testing with a 3.5mm plug in the jack using an ohm meter.? That way, you would know that it is the correct trace. 73 Evan AC9TU |
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An alternate to cutting a trace would be to handle the modifications at the LM386 IC.
e.g. Pull the IC out of the socket, bend up the pin for the node that you want to insert the filter in-line. you may also want to do the LM386 bass boost enhancements while you are at it.? Evan posted the way he did it. |
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Here is the message with the "Hiss" reduction:
/g/BITX20/message/82944 It was based on information from the TI LM386 datasheet: Another change is not in the email thread posted above:? This is for when you need the extra gain.? The recommended feedback capacitor is 10uF.? The stock uBitx v5 and v6 have only 1uF.? This will work at the expense of lower gain at low frequencies.? This will not help if you limit the gain to only 20. The uBitx series was always a cost tradeoff.? Surprisingly, Ashhar Farhan could get the performance at the cost that HFSignals sold the rigs. 73 Evan AC9TU |
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On Tue, Jan 10, 2023, at 12:30 PM, <johnroland51@...> wrote:
Curt, Evan, GaryJohn, I used an opamp based 700 Hz filter on one of the v6 radios I modified.? To avoid cutting the trace, I moved the filter to before the LM386 audio amp.? That way, I could add a switch to run SSB without the filter.? That worked for both the headphones and the speaker.? The result was to tap into the Audio Header for the VOL-M input to the filter and send the filter output to the isolated pin 3 of the LM386.? I used a 2 position switch to select either the normal input or the output of the filter.? As long as you only want the headphones for the filtered CW signal, then your approach is better.? If you wish to also use the headphones with SSB, or you want CW on the speaker, the switching gets complex if you move it to the headphone line. Note that the "Audio" header is still included in the v6 radios.? This is a convenient place to tap in for audio signals. 73 Evan AC9TU |
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Evan,?
Thanks for the suggestion.? I implemented your idea and am very happy with the results.? Adds a little selectivity and really cuts down the background noise, ? I used a dpdt switch so I can switch the filter in and out.? Took filter audio in from pin 5 of the Audio Header through the switch, Audio Header pin 8 for audio ground. ? Filter audio? out to pin 3 of the LM386, through the switch.? Power to the filter from the P5 header. Wired with arduino jumpers which fit the headers nicely. ? No traces cut, totally reversible except for a hole in the case for the switch. ?? 73? /John W7SWB |
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Here's an update on my attempt to insert a cw audio filter in my V6.
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As it turns out the configuration described in #99019 did work very well for reception, but when I transmitted I got an annoying thump when the ptt cycled.? I messed around with shielding my filter in an altoids tin and straightened up my messy wiring to no avail.? in the mean time I've been operating with a remote cw filter which did not thump.?? That got me wondering if placing the internal cw filter behind the audio amp like it is when I use the remote filter might solve the problem.?? I ended up bending IM386 pin 5 parallel to the board, attaching a female arduino jumper wire between pin 5 and my cw filter input and using a male jumper with the pin bent in an "L" shape between the now vacant pin 5 socket and the filter output.? Its all wired up with a dpdt switch so I can switch it in and out. The thump has gone away! ? Only down side is that my filter distorts at around 75% volume, which is more than I ever use so not really a problem.
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Anxiously awaiting the chance to order my zbitx.
73
/John
W7SWB |
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