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RX trouble
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Woody
开云体育Hi Guys, Just finished the ubitx v4 and began to test.? Have a problem and sure would like some suggestions. I have a power audio amp IC outboard (supplies ~500 ohm load to uBITX) to better drive a speaker.? That checks out fine. However, the RX is not working properly.? Deaf RX and low audio.? Started with all "stock".? Also seemed 2-3 KHz off freq and bad audio.? Tried Calibration & BFO set.? No go. Then, loaded CEC v1.1 firmware.? Still an issue.? Did "Factory Reset"... Ran Calibration & BFO using a TXCO 20 MHz oscillator signal. Originally, zero beat readout was ~1997 (?) It now zero beats the 20 MHz reference when the frequency indicates 20.000. It also (best I can tell listening to myself - see comments on audio files below) sounds OK when I transmit SSB and listen on another receiver.? FWIW - Power out varies depending on band. ...e.g. 7 MHz, 5 watts; 10-18 MHz, 10 watts. If I TX (dummy load) a SSB signal from my "big" rig, it sounds OK on the uBITX receiver. Almost working, but the receiver is stone deaf!? It will hear my 20MHz osc and the other SSB transmitter but it takes a very strong signal (I don't have an amplitude calibrated HF sig gen). When I attach a antenna, no increase in the noise.? Nothing at all can be heard.? Listening on 40M (where I hear signals S9 in the other rig) I can barely hear anything. Need suggestions on how to fix... Audio files attached:? 2_1_0? KHz tune - ? Tuning in 1 Kz steps (USB), 2 KHz down from oscillator, 1 KHz down, and zero beat (20.000 MHz) SSBsignal -? A S9 station. Very low output level and distorted. Very Strong SSB RF - From my big rig a few feet away.? Couldn't hear it when on dummy load, had to switch the big rig to an antenna... So, to sum it up...? Freq readout now OK, but very, very poor RX sensitivity and distortion, regardless of band. HELP!? Thanks, Woody, KZ4AK 2_1_0 KHz tune.mp3
2_1_0 KHz tune.mp3
SSBsignal.mp3
SSBsignal.mp3
Very strong SSB RF.mp3
Very strong SSB RF.mp3
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You might check out this debug procedure for the Bitx40 receiver.
Farhan takes a 3 foot or so piece of wire as an antenna to pick up local QRM, uses that to inject noise into each stage of the receiver starting at the audio amp. Noise should increase with each stage of amplification, when you find a stage where that is not the case then you have localized the problem. My guess is a broken toroid wire, or perhaps a cold solder joint on one of those wires where the enamel didn't quite get scraped off well enough. In some cases, you can check out those connections with an ohmmeter. Jerry |
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Woody
After countless calibrate and BFO sessions (employing various techniques) and lowering the attenuation to the outboard amp, I have improvement.? ...But I would not call it total success.
Have not measured the audio level from the board exactly, but appears to be ~ 1 volt rms max into 600 ohms - when maxed out on a 800 Hz tone.? I was expecting more.? I increased the level to the off board amp (potientiometer adjustment) and can now hear some noise when connecting an antenna. The last adjustment of CAL and VFO (sort of) works.? Zero beat is now about 200 Hz off my reference oscillator, but at least close... Received SSB audio is not as clean as I would like and rather "pinched".? Tuning the VFO on a signal to achieve a understandable voice is *extremely* critical.? A few 10s of Hz off frequency leads to garbled audio. ? No BFO setting I tried has improved these observations.? The change with BFO adjustment is subtle, but where I wound up, 11997.04 worked, albeit with the two issues mentioned. I get the vague impression that the band pass filter might be very narrow. ??????? ...Or am I still way off in my adjustments. ? I attached a mp3 of the best audio so far.? It is usable, but has a narrow bandwidth.? Moving the BFO to lower the band pass pitch lowers ineligibility. Am I expecting too much?? I welcome more comments and suggestions. Thanks, Woody, KZ4AK -- |
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Woody
Mine arrived with LSB vfo way off, but USB seems okay. Yes as desired not much extra bandwidth in the xtal filter. You will appreciate the rig not having gobs of extra gain. It allows agc to be added perhaps even in the audio portion. Take some time to experience the rig. In headphones on 40m you may find signals rather light, but in evening dreadfully loud. This is what we should have. I haven't tried my audio agc yet, but I suspect something simple enough will do fine. Excuse me the backseat driver, but I suggest taking smaller steps with firmware and hardware. All may be well once you experience it, and later improve it to your liking. I would not sweat frequency accuracy yet, but do optimize the bfo. Fellow builder, Curt |
开云体育Hi Woody, I've had about the same grade? of SSB, closer or higher power stations can come in very nice and clear. But most SSB can sound like that depending on where it fall on the filter edge. I've listened to stations on 80 and 40 in Plano, Texas, Florida, Georgia, and Kansas that sound great. From my experience using ear buds puts out the best sound, head phones seem to be harder to drive for the audio portion of the uBitx. The cw sounds really good on both bands, I've tried listening for any 10m traffic but haven't heard much in my local area. KE8KNK --Kyle On 10/23/2018 09:06 PM, Curt via
Groups.Io wrote:
Woody |
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Gordon Gibby
开云体育It’s been a while, but I think I calibrated the main oscillator by commanding it to 10 MHz and then measuring the frequency with a small piece of wire near it going into an Icom 718. ?Then put the proper constant into the software.?From there, use any digital software that lets you see the power across the ?audio spectrum and adjust while listening to galactic White Noise, so it is in the proper audio passband. ? If my memory is correct, my passbands were a bit narrow. ? You could
use free FLDIGI or probably any of a zillion other products.
Gordon
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开云体育Thanks Gordon...much appreciated. ? 73 Roger ? Sent from for Windows 10 ? From: Gordon Gibby
Sent: Wednesday, 24 October 2018 7:12 PM To: [email protected] Subject: Re: [BITX20] RX trouble ? It’s been a while, but I think I calibrated the main oscillator by commanding it to 10 MHz and then measuring the frequency with a small piece of wire near it going into an Icom 718. ?Then put the proper constant into the software.? ? From there, use any digital software that lets you see the power across the ?audio spectrum and adjust while listening to galactic White Noise, so it is in the proper audio passband. ? If my memory is correct, my passbands were a bit narrow. ? You could use free FLDIGI or probably any of a zillion other products. ? Gordon ?
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Gordon Gibby
开云体育I may have put on GitHub ?the little software to upload to the uBitx ?to get it to go to a certain freq. ?The idea was to get it to go to the frequency of the Crystal itself: so phase locked loop was 1 to 1Then whatever frequency you measured tells you how far off the crystal is , mine were about 3 kHz off; if you’ve already adjusted your frequencies correctly you may not need this
Then just use a waterfall looking at White Noise to set the BFo frequency to get the right audio pass band. If you change it but too much there’s a chance you’ll flip sidebands, ?but I bet most people won’t. ?
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Woody
Thanks for all the suggestions!?? I plan to give some a try.? I agree that setting alignment is not trivial.? I also agree that CW seems OK.? Tuning around, the BW seems near what I would expect for SSB filtering and distortion is minimal.? My scratch built SSB rigs were really easy by comparison.
The "pinched" SSB audio is an annoyance, but not a show-stopper. The need to be dead-on frequency for decent SSB is more of an issue.? When listening to QSOs, the symptom is apparent - If tuned for good audio on station 1, and station 2 is just a bit off freq, it is hard to understand.? ...It is that critical.? Possibly a result of the filter's narrow bandwith / center position?? More tweaking may help.? I have a broadband RF noise generator (homebrew, of course) and PC audio spectrum analyzer used to align my Elecraft K2.? May give that a try.?? The BFO adjustment is a pain.? There is some, but not much change with lots of encoder spinning.? Wonder if I will wear out the encoder before it is done. ;) Best I can tell, my TX audio is OK, but hard to tell exactly when listening to myself.? No on-air tests yet. An AGC is also on my agenda, have Axicom relays and replacement inductors, but want to get the board functioning as well as possible before jumping in with modifications. Have archived the replies and the testing continues... 73, Woody, KZ4AK |
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Woody?
I just listened to your sound clips and I heard distortion that’s usually produced when a source signal overdrives the next stage. Where are you connecting your outboard amp? I would think that you would get distortion if you connected it to the speaker out (8 ohm impedance). I would tap the audio at the volume pot (top lug) if you haven’t already.? |
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Thanks Gordon... I have been working on this for about 5 weeks.My project was to replace the Tx and Rx of an old Kenwood TS120S with the uBitx. This I have done and have improved the receiver by adding audio filters. It now runs 100watts and I am quite pleased with it But this calibration thing has got the better of me. I have read so many conflicting instructions abt how to do it. I notice last night that my BFO changes are not being saved! This kind of event drives me nuts. How do you save your changes? 73 Roger On Thu, 25 Oct 2018 12:28 am Gordon Gibby <ggibby@...> wrote:
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Gordon Gibby
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Thanks for ?your reply Gordon I have not upgraded my software (ver 4.3) yet. The instruction I received originally for changing values for calibration and BFO were some how out of date. They would not work with my software.? The procedure for saving changes appears to me to very often not work. After making changes I exit SeTTINGS then exit MENU then switch off the rig and wait ten secs. Sometimes it works sometimes not....... 73 On Thu, 25 Oct 2018 at 08:14, Gordon Gibby <ggibby@...> wrote:
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I have this done now and it appears to be "all good". But I did it by tweaking until I got it right on. Gordon's advice about using a viewer was good, and I did use the WSJT X software viewer. This must be about the worst method of aligning a Tx/Rx I have ever seen. Perhaps it wouldn't be so bad if there was some instruction sent with the rig from the factory. It appears there are several methods that might or might not work.? My next task is to make it CAT capable.... The old TS120S now has a new lease on life. Despite all the talk of the Tranmission being dirty I have not yet see any sign of that practically. I think this is because I use a very low drive level by changing RV 1 to a 50 Kohm pot and limiting output to 100 watts. The TS 120 amplifier has inbuilt filtering too.? Thanks for your interest. 73 Roger ZL2RX ? |
