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#uBiTx CW RF power out
#ubitx
¿ªÔÆÌåÓýI received my uBiTx about two weeks ago.? I experienced some of the same issues that others have reported: 1.????? I did find that the wiring diagram for the three 3.5mm jacks to be confusing and the pin numbers/locations on the supplied jacks did not match the drawing. 2.????? I smoked U1. Probably because I plug a speaker with a tip/sleeve into the Speaker jack.? I found that the NTE7155 is suppose to be a replacement and I could find one locally.? I did use an IC socket so I can easily replace it with a TDA2822 if necessary.? I also disconnected the audio out from the ring of the Speaker jack as a precaution. 3.????? I also did not have any current variation after the PA bias was set.? This was because I miss wired the electrets mic. 4.????? The first signal reports were the audio was poor with too much high frequencies and no mid to low. ?Before I tackle the audio issue I want to get a handle on the RF power out. 5.????? The CW RF power out is more than I expected.? The below table shows some of the measurements that I see on my setup. ( Yes I know that some of the results are counter intuitive.? Unless someone knows otherwise will write it off to change in biasing in one or more circuits):
? I also set the PA bias in using an oscilloscope at the antenna connector connected to a dummy load and adjusting Rv2 and Rv3 alternately in 5 Volt increments until the Wattmeter showed 10 Watts. My question is how to set the maximum power? Use Rv2 and Rv3 to set the bias or use Rv1 to back off the drive after the bias has been set using Rv2 and Rv3. ? Bob ¨C KE7JL ? ? |
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Set bias for 100ma of drain current on each IRF510 using RV2 and RV3 and then leave it be.
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That 100ma shouldn't change much even if you were to go from a 12v PA-PWR to 24v.? Adjust power level using RV1 on the uBitx.??(RV1 sets IRF510 drain current on the Bitx40) For SSB, could also vary power level by adjusting the mike gain at Q6 somehow. I assume the smoked U1 was marked "WX".? Can you verify? The WX clones blow for no particular reason. The WX probably works reliably if the supply voltage is reduced to 5v or so, down from 12v. Search for "TDA2822" in this forum to see some nice long discussions The NTE7155 will probably work fine, perhaps you could report back on that too. > The first signal reports were the audio was poor with too much high frequencies and no mid to low. Sounds like the 12mhz bfo is positioned incorrectly relative to the passband of the crystal filter. Should be able adjust your audio (both transmit and receive, affects both equally) by using the calibration routine in the Raduino for the bfo frequency adjust. Jerry, KE7ER On Mon, Mar 5, 2018 at 07:23 pm, Bob wrote:
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Sorry for the delay, but life does get in the way once in a while.
It looks like a lot of the ink went with the smoke but under the right light I could make out WX 16403HN.? ?The NTE7155 appears to be working ok. However, I am not going to give it the smoke test by shorting out the output.? ?If I am ordering parts from someone that also has the TDA2822 I will buy a couple and run a comparison. ?My next step is to quantitatively set the BFO.? With the equipment I have I should be able to get some repeatable numbers. Thank for the feedback.? The spirit of Amateur Radio is alive and well :-) Bob - KE7JL? |
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On Mon, Mar 5, 2018 at 07:46 pm, Jerry Gaffke wrote:
Set bias for 100ma of drain current on each IRF510 using RV2 and RV3 and then leave it be. ?Hi Jerry I have an FCI/FOI TDA in my ubitx batch 2. It is very hot indeed after rig on for an hour.is there an over voltage issue to the chip? Thank you again for all your help getting it going again with the RF510. -- MM?WXT GQRP - #15057 |
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Alan,
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Pretty much all reports of blown TDA2822's have been with the "WX" branded clones, they can blow catastrophically if fed 12v.? Even the WX parts seem to work fine if the board is modded to add a voltage regulator so they only see 5 or 6 volts instead of 12 volts. I have not heard of trouble with the FCI branded TDA2822's, even at voltages over 12v. Though they will get hot if they are asked to deliver too much power to the load. Do you have the volume turned way up? Does your chip still get hot if your turn the volume control all the way down? If the chip gets hot at moderate volumes, but is not hot when the volume control all the way down, perhaps you simply have a defective speaker, try switching speakers. Could be that there are ultrasonic tones coming from the receiver that the TDA2822 is dealing with that you can't hear, causing the chip to overheat. ? ??/g/BITX20/message/40038 Could be that there are ultrasonic oscillations at the TDA2822 for some reason, though there have been no reports of that in the forum. Those last two possible faults could best be seen with an oscilloscope, though it wouldn't have to be a very good one.? Here's one that's not very good ???/g/BITX20/message/40977 but should be adequate for looking at audio issues and is very cheap: Better yet, ask around at a ham club, see if somebody with a scope will look at it with you. Jerry, KE7ER ? On Fri, Apr 13, 2018 at 06:06 pm, Alan -MM?WXT wrote: I have an FCI/FOI TDA in my ubitx batch 2. It is very hot indeed after rig on for an hour.is there an over voltage issue to the chip? |