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Re: Poor RX sensitivity, no RF out -
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Pat and Bill..,
you are temptimg me :-) I have some old 2N2222 with metal case, gold in colour... That one should look like nice, a giant in the Lilliput town of the smd population :-) Me too, I thing installing a couple of protection diodes is a good idea. Will do. Cheers Jep |
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Re: Poor RX sensitivity, no RF out -
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Bill I replaced Q90 on top of the board after removing the 2N3904. I just shortened the leads and bent them to fit the pads before tack soldering it in.
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Skip Davis, NC9O On May 13, 2020, at 11:05, Bill Cromwell <wrcromwell@...> wrote: |
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Re: Poor RX sensitivity, no RF out -
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Ray,
Voltages are 12V on Collector and 0.5V, the same on Base and Emitter. So the Base-Emitter junction is shorted and that should explain not only the missing of RF-out, but also the reduced sensitivity of the receiver. Thank you, again, have a good night, I wish you all the best Jep |
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Re: Poor RX sensitivity, no RF out -
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Jepp,
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I cant let you go before I sleep peacefully! What was the TX voltages of Q90? Raj At 13/05/2020, you wrote:
Bingo! |
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Re: Poor RX sensitivity, no RF out -
#v3
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Bingo!
Raj, David and Jonas you are right! Q90 on my ubitx seems to be blown! The multimeter shows about 230 ohm on the junctions. I did not yet check the voltages but I did this: Using a short wire and two thin pins I just touched the Base of Q90 and the cursor of RV1, thus I bypassed Q90: then pressing the key some RF out from the PA immediately pop-up nicely!? Thank you all my friends for the kind and smart expertize! Now, to complete the job the matter is...: I do not have a 2N3904 SMD at hand. Should I order it online or install an ordinary 2N2222 (non SMD) instead? Well... I do not urge to have the ubitx?working tonight, so it is certainly best to wait and do a proper job.? In the meanwhile, just to fill the present boring days, I will play with a single-tube xtal transmitter 1938-style :-) Let me add a comment: This is the first time I asked for help on this Group and I have been delighted by the quick, very kind and smart response of so many friends that helped getting out of trouble. Truly amazing. Thank you all from my deep heart. Best regards Jep, IZ0WIT |
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Re: uBitx V4 for sale
If they are working units - I will take it 73 Lou KI5FTY On Wed, May 13, 2020 at 9:05 AM John Veach <ke4d@...> wrote: I have two V4 that are surplus to my needs. (V6 arriving this week). One with a Nextion display running KD8CEC software if I remember correctly that I use on CW only. I did put a four pin mike connector in the case but never acquired a microphone for it. Never hooked up the straight key jack just a paddle for cw. It¡¯s in an aluminum case I got from SkyCraft in Orlando and also has a 12 v fan built in. I will throw in the other V4 which has no display and I haven¡¯t looked at it for a while!? Going to list on QRZ but wanted to put them here first.? Will ship both U.S.A. for $100 ? |
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Re: Poor RX sensitivity, no RF out -
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I used another transmitter close to my v3 and blew q90. Replaced q90 and all was good. Dave? kc2ipx On Wed, May 13, 2020 at 9:18 AM Raj vu2zap <rajendrakumargg@...> wrote: Also check Q90 EBC voltages. We have to eliminate a possible short of Q90 EB junction. |
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Re: Poor RX sensitivity, no RF out -
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Also check Q90 EBC voltages. We have to eliminate a possible short of Q90 EB junction.
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Raj At 13/05/2020, you wrote:
That you Ray, I will do that immediately. |
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Re: Poor RX sensitivity, no RF out -
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That you Ray, I will do that immediately.
Jep |
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Re: Poor RX sensitivity, no RF out -
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Just for info, now I completed the re-soldering of all the thru-hole joints of the ubitx board. But the problems remained unchanged.
So..., I must argue it is time to check individual transistors and diodes, starting from the front-end as suggested by Jonas. As already briefly mentioned, here at my "marine" location some 50 km North of Rome I only have a digital multimeter instrument, and by now (due to pandemia lock-down) there is no chance to move to Rome and access an oscilloscope or whatsoever... Let's consider that an exercise for emergency conditions: Use more the brain instead of sofisticated instruments :-). Cheers Jep |
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Re: Poor RX sensitivity, no RF out -
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This tells me the issue is with L1-4 T1 T2 or mixer diodes. check R100-103 for value and solder.
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Raj At 13/05/2020, you wrote:
Yes, it is exactly so.... so it is confirmed no RF reach the PA while I push the key in CW or speak on the microphone. |
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Re: Poor RX sensitivity, no RF out -
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Yes, it is exactly so.... so it is confirmed no RF reach the PA while I push the key in CW or speak on the microphone.
Jep |
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Re: Poor RX sensitivity, no RF out -
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Well.... yes, this might have happened. I had some other 100W trx on the same desk before, so I cannot exclude some RF entered the ubitx while I was transmitting using something else. I have only a dipole, but the antenna-switch was common to three transceivers.
How could I check if Q90 and the diode bridge are fried? Bests Jep |
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Re: Poor RX sensitivity, no RF out -
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Hi Dave,
no, it is not 6A.... it is just 0.6A which I think is the idling current on transmit (it is 0.12A on receive). When I press down the key or speak on the microphone it remains the same, which means no RF at all arrives to the PA input. My ubitx V3 has been not modified at all, I only added an audio filter for CW and a CW keyer: these are separate boards not affecting at all the ubtix main board. Such add-ons have been working for long time before the present problem surfaced. 73 Jep |
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Re: Poor RX sensitivity, no RF out -
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It's 0.6A which is correct with no modulation!
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Raj At 13/05/2020, you wrote: 6 amps is not normal on key down. Normal is something like 2+ amps. |
Jep
Skip Davis
Raj vu2zap
David Nelson