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The only diode needed on Q90 is one to prevent reverse voltage damage. ??
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On Nov 2, 2020, at 11:59, Kit Peters <popefelix@...> wrote:
? oh, and I removed the diodes.
On Mon, Nov 2, 2020 at 10:58 AM Kit Peters < popefelix@...> wrote: I'll check all that, thanks.
As for test equipment, I have both a DMM and an old oscilloscope.
Kit,
I would expect a transmission of 15W a short distance away to create a very strong signal in an unshielded uBitx.
Perhaps you also have a problem in receive, but for now I will assume that is not the case.
The fact that you receive any signal at all with the uBitx tuned to display the same frequency as your transmitter
suggests the receiver is mostly working.? You may have trouble where the diodes were added if that was done incorrectly.
I would suggest not doing mods until everything the stock rig is working properly.
When debugging the transmitter, I would start with CW mode as Even suggested in post 83195:
>? Verify the transmit power using CW, not SSB.
There is a lot less to go wrong when transmitting in CW mode.
Put a good dummy load on the antenna terminal, put the uBitx in CW mode,?
and press the CW key to transmit.? The DC voltage on both ends of R84 should be 12 volts
when transmitting, and PA-PWR into L9 should also be 12 volts DC.
Put your finger on the IRF510 heatsinks and the dummy load occasionally,
let up on the key for a few minutes if they get too warm.
Put a 6" piece of wire on the base of Q90 as an antenna, see if you can hear the transmit
signal on a nearby receiver when you hold the key down.
If the above steps check out, take DC voltage readings for the stages from Q90
on out through the IRF510's, compare to those on pages 13, 14, and 15 of this document:
? ?
That is a fairly complete debug guide for the v3 uBitx.
Let us know how far you get.? If you need further help, let us know what
instruments you have available.? I assume you have a DVM.
Do you have access to a diode RF probe, or better yet an oscilloscope?
Good luck, this may prove to be educational.
If you can get help from a ham at a nearby club who has a bench full of instruments
and experience with troublshooting, that would help this process considerably.
Jerry, KE7ER
On Mon, Nov 2, 2020 at 07:20 AM, Kit Peters wrote:
I haven't dug into this in depth, but I did test receive last night. Pumping 15 W into my loop with a borrowed Kenwood TS-2000 I was able to (faintly) hear my transmission in a dummy load. I suppose I could have stuck a piece of wire into a UHF connector and made a quickie vertical as well, but that was what occurred to me at the time. :)
--
Kit Peters, W0KEH GPG public key fingerpint:? D4FF AA62 AFEA 83D6 CC98 ACE5 6FAE 7E74 7F56 ED1DHello to any and all NSA, DEA, or other government or non-government agents reading this email.? Tell me about your life; I'll tell you about mine.
-- Kit Peters, W0KEH GPG public key fingerpint:? D4FF AA62 AFEA 83D6 CC98 ACE5 6FAE 7E74 7F56 ED1DHello to any and all NSA, DEA, or other government or non-government agents reading this email.? Tell me about your life; I'll tell you about mine.
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I was going off of Evan Hand's mod ( /g/BITX20/message/83186) which has two diodes, one opposite the other, across two of the pins on K1.
The only diode needed on Q90 is one to prevent reverse voltage damage. ?? ? oh, and I removed the diodes.
On Mon, Nov 2, 2020 at 10:58 AM Kit Peters < popefelix@...> wrote: I'll check all that, thanks.
As for test equipment, I have both a DMM and an old oscilloscope.
Kit,
I would expect a transmission of 15W a short distance away to create a very strong signal in an unshielded uBitx.
Perhaps you also have a problem in receive, but for now I will assume that is not the case.
The fact that you receive any signal at all with the uBitx tuned to display the same frequency as your transmitter
suggests the receiver is mostly working.? You may have trouble where the diodes were added if that was done incorrectly.
I would suggest not doing mods until everything the stock rig is working properly.
When debugging the transmitter, I would start with CW mode as Even suggested in post 83195:
>? Verify the transmit power using CW, not SSB.
There is a lot less to go wrong when transmitting in CW mode.
Put a good dummy load on the antenna terminal, put the uBitx in CW mode,?
and press the CW key to transmit.? The DC voltage on both ends of R84 should be 12 volts
when transmitting, and PA-PWR into L9 should also be 12 volts DC.
Put your finger on the IRF510 heatsinks and the dummy load occasionally,
let up on the key for a few minutes if they get too warm.
Put a 6" piece of wire on the base of Q90 as an antenna, see if you can hear the transmit
signal on a nearby receiver when you hold the key down.
If the above steps check out, take DC voltage readings for the stages from Q90
on out through the IRF510's, compare to those on pages 13, 14, and 15 of this document:
? ?
That is a fairly complete debug guide for the v3 uBitx.
Let us know how far you get.? If you need further help, let us know what
instruments you have available.? I assume you have a DVM.
Do you have access to a diode RF probe, or better yet an oscilloscope?
Good luck, this may prove to be educational.
If you can get help from a ham at a nearby club who has a bench full of instruments
and experience with troublshooting, that would help this process considerably.
Jerry, KE7ER
On Mon, Nov 2, 2020 at 07:20 AM, Kit Peters wrote:
I haven't dug into this in depth, but I did test receive last night. Pumping 15 W into my loop with a borrowed Kenwood TS-2000 I was able to (faintly) hear my transmission in a dummy load. I suppose I could have stuck a piece of wire into a UHF connector and made a quickie vertical as well, but that was what occurred to me at the time. :)
--
Kit Peters, W0KEH GPG public key fingerpint:? D4FF AA62 AFEA 83D6 CC98 ACE5 6FAE 7E74 7F56 ED1DHello to any and all NSA, DEA, or other government or non-government agents reading this email.? Tell me about your life; I'll tell you about mine.
-- Kit Peters, W0KEH GPG public key fingerpint:? D4FF AA62 AFEA 83D6 CC98 ACE5 6FAE 7E74 7F56 ED1DHello to any and all NSA, DEA, or other government or non-government agents reading this email.? Tell me about your life; I'll tell you about mine.
-- Kit Peters, W0KEH GPG public key fingerpint:? D4FF AA62 AFEA 83D6 CC98 ACE5 6FAE 7E74 7F56 ED1DHello to any and all NSA, DEA, or other government or non-government agents reading this email.? Tell me about your life; I'll tell you about mine.
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I think two diodes should work fine.
Gordon is saying that one diode might be sufficient,?
since the base-emitter junction of Q90 can work as the second diode.
He could be right.
Though that 2n3904 base-emitter junction is rather wimpy,
and an asymetrical signal may be worse than clipping top and bottom equally.
The AC coupling into the Q90 base also complicates things.
Not obvious to me what's best.
Jerry, KE7ER
On Mon, Nov 2, 2020 at 09:23 AM, Kit Peters wrote:
I was going off of Evan Hand's mod ( /g/BITX20/message/83186) which has two diodes, one opposite the other, across two of the pins on K1.
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I really didn¡¯t use mine an awful lot after I installed one diode, but I never ever had a Q90 go bad.
My previous discussion of the failure mode suggested that it was reverse voltage, as that coupling cap charges up. Having a reverse diode prevents that.
There¡¯s nothing terribly wrong with having two ; it just may raise other issues that I never thought through.
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On Nov 2, 2020, at 13:25, Jerry Gaffke via groups.io <jgaffke@...> wrote:
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All of the receiver front end protection that I found on the net used two diodes as I had them configured.? The worst case I believe is that the second diode would be redundant and the best would provide the symmetrical signal clipping.? The one improvement is to add the 6.3-volt incandescent lamp to dissipate the energy between the two relays.
73
Evan
AC9TU
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Gordon, I had read your argument long ago and for some reason I don't remember
this point about the C80 charging up.? Good point.
Jerry, KE7ER
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On Mon, Nov 2, 2020 at 10:58 AM, Gordon Gibby wrote:
My previous discussion of the failure mode suggested that it was reverse voltage, as that coupling cap charges up. Having a reverse diode prevents that.
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It took me a while to understand it. Basically, as designed, the transistor base to emitter junction And the couple and capacitor form a half wave rectifier power supply. Charging up the coupling capacitor. Until eventually the peak inverse voltage required of the basement or Junction is exceeded, and the transistor is destroyed and the coupling capacitor form a half wave rectifier power supply, driven by a strong RF signal acting like the AC input. Charging up the coupling capacitor. Until eventually the peak inverse voltage required of the base emitter junction (usually only five or six volts) ?is exceeded, and the transistor is destroyed?
Way back in the old days we were all taught how to figure out what reverse voltage capacity is needed by the diode in a half wave power supply
By adding a reverse diode across the base emitter, you stop that power supply effect. ?
Now the coupling capacitor has current moving in both directions, and can¡¯t destroy the transistor?
Gordon
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On Nov 2, 2020, at 15:26, Jerry Gaffke via groups.io <jgaffke@...> wrote:
?Gordon, I had read your argument long ago and for some reason I don't remember this point about the C80 charging up.? Good point. Jerry, KE7ER On Mon, Nov 2, 2020 at 10:58 AM, Gordon Gibby wrote:
My previous discussion of the failure mode suggested that it was reverse voltage, as that coupling cap charges up. Having a reverse diode prevents that.
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The audio is very scratchy on my Ubitx V3. What needs to be done.
It took me a while to understand it. Basically, as designed, the transistor base to emitter junction And the couple and capacitor form a half wave rectifier power supply. Charging up the coupling capacitor. Until eventually the peak inverse voltage required of the basement or Junction is exceeded, and the transistor is destroyed and the coupling capacitor form a half wave rectifier power supply, driven by a strong RF signal acting like the AC input. Charging up the coupling capacitor. Until eventually the peak inverse voltage required of the base emitter junction (usually only five or six volts) ?is exceeded, and the transistor is destroyed?
Way back in the old days we were all taught how to figure out what reverse voltage capacity is needed by the diode in a half wave power supply
By adding a reverse diode across the base emitter, you stop that power supply effect. ?
Now the coupling capacitor has current moving in both directions, and can¡¯t destroy the transistor?
Gordon ?Gordon, I had read your argument long ago and for some reason I don't remember this point about the C80 charging up.? Good point. Jerry, KE7ER On Mon, Nov 2, 2020 at 10:58 AM, Gordon Gibby wrote:
My previous discussion of the failure mode suggested that it was reverse voltage, as that coupling cap charges up. Having a reverse diode prevents that.
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For scratchy audio on a V3, could be in the TDA2822 amp. An easy way to check this is to take the VOL-M wire from the volume control pot, detach that wire from the TDA2822 pin 7, then connect that wire plus a ground up to some other audio amplifer.? This could be the auxiliary input of a hifi stereo, or it could be an LM386 module such as this:? ? ?? If that sounds good, then the problem is in the TDA2822 stage. We did have some trouble with the "WX" version of the TDA2822 blowing up: ? ?? /g/BITX20/message/64247?p=,,,20,0,0,0::Created,,tda2822+ke7er,20,2,0,29417614The TDA2822's marked "FCI" pretty much all did fine. I don't recall reports of bad audio on the TDA2822's, other than no audio after they blew up. The v4 uBitx with the discrete transistor audio amp did have scratchy audio due to crossover distortion, if you have a v4 then replacing that part of the circuit with an LM386 module as described above is a good solution. ? It is possible that your bad audio is in the pre-amp at Q70, or in the demodulator. But I would try replacing the TDA2822 stage as described above first. Jerry, KE7ER
On Tue, Nov 3, 2020 at 09:52 AM, rajesh huddar wrote:
The audio is very scratchy on my Ubitx V3.
What needs to be done.
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Thanks , will try replacing the TDA 2222 and if that doesn't work them will use the LM386 amp
For scratchy audio on a V3, could be in the TDA2822 amp.
An easy way to check this is to take the VOL-M wire from the volume control pot,
detach that wire from the TDA2822 pin 7, then connect that wire plus a ground up
to some other audio amplifer.? This could be the auxiliary input of a hifi stereo,
or it could be an LM386 module such as this:?
? ??
If that sounds good, then the problem is in the TDA2822 stage.
We did have some trouble with the "WX" version of the TDA2822 blowing up:
? ??/g/BITX20/message/64247?p=,,,20,0,0,0::Created,,tda2822+ke7er,20,2,0,29417614
The TDA2822's marked "FCI" pretty much all did fine.
I don't recall reports of bad audio on the TDA2822's, other than no audio after they blew up.
The v4 uBitx with the discrete transistor audio amp did have scratchy audio due to crossover distortion,
if you have a v4 then replacing that part of the circuit with an LM386 module as described above is a good solution.
?
It is possible that your bad audio is in the pre-amp at Q70, or in the demodulator.
But I would try replacing the TDA2822 stage as described above first.
Jerry, KE7ER
On Tue, Nov 3, 2020 at 09:52 AM, rajesh huddar wrote:
The audio is very scratchy on my Ubitx V3.
What needs to be done.
|
Hello everyone, I would like to trace the cause of not having RF output on the PA of the uBITX v4, under the load of 50 Ohms resistive. Could someone post the waveforms on the oscilloscope at the different test points? The IRF510 output is burning. 73's PY2PVB Rubens Kamimura
Em ter., 3 de nov. de 2020 ¨¤s 16:44, rajesh huddar < pumerah@...> escreveu:
Thanks , will try replacing the TDA 2222 and if that doesn't work them will use the LM386 amp
For scratchy audio on a V3, could be in the TDA2822 amp.
An easy way to check this is to take the VOL-M wire from the volume control pot,
detach that wire from the TDA2822 pin 7, then connect that wire plus a ground up
to some other audio amplifer.? This could be the auxiliary input of a hifi stereo,
or it could be an LM386 module such as this:?
? ??
If that sounds good, then the problem is in the TDA2822 stage.
We did have some trouble with the "WX" version of the TDA2822 blowing up:
? ??/g/BITX20/message/64247?p=,,,20,0,0,0::Created,,tda2822+ke7er,20,2,0,29417614
The TDA2822's marked "FCI" pretty much all did fine.
I don't recall reports of bad audio on the TDA2822's, other than no audio after they blew up.
The v4 uBitx with the discrete transistor audio amp did have scratchy audio due to crossover distortion,
if you have a v4 then replacing that part of the circuit with an LM386 module as described above is a good solution.
?
It is possible that your bad audio is in the pre-amp at Q70, or in the demodulator.
But I would try replacing the TDA2822 stage as described above first.
Jerry, KE7ER
On Tue, Nov 3, 2020 at 09:52 AM, rajesh huddar wrote:
The audio is very scratchy on my Ubitx V3.
What needs to be done.
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Aurelia Fenderson-Peters
rajesh huddar