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Continuity
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College Professor Simon Thompson
I am wiring up my BitX40, and in the process, have been checking for continuity as I go. I attached all of the power connectors, and seemed to be getting what appears to be continuity. I took some measurements, because I initially thought that I had mistakenly attached a wire to an incorrect point. But after removing all wiring and taking some measurements from the PWR1 1 and PA-PWR 1 connectors, this is what I observed: measured resistance between positive and negative at PWR 1 about 3.13 KOhm measured resistance between positive and negative at PA-PWR 1 about 40 MOhms, then declines measured resistance between positive terminal at PWR 1 and positive terminal at PA-PWR 1 about 15 MOhms then declines
I am not an electronics engineer, but to me, I should not have any continuity between positive and negative terminals. What tipped me off to the problem was continuity between positive and negative at the main power socket for the barrel connector. I have not applied power to the radio, so I am hoping that there is some simple explanation for this, and a similarly simple fix. Does anyone know what might be happening? Does anyone know where I can look on the board for a reasons for this apparent continuity? |
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Main 12v PWR to GND will be just a few kohm due to bias resistors, for example the path through R13,14,15,16 in the upper left of the schematic. PA-PWR to GND resistance will gradually increase (not decline) as C157 charges up, Q15 is off with no power applied and the current has nowhere else to go. Your board is probably just fine. On Sun, Mar 26, 2017 at 12:15 pm, College Professor Simon Thompson wrote:
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Simon Thompson
开云体育Thanks!
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I measured 3.1 kOhm at main PWR. So same like with your rig. Measuring ?PA-PWR ?between + and GND ?is around 60 MOhm (starting with lower value as Jerry explained) and switching test leads on this connector gives about 40kOhm after a few seconds. Having high resistance here on your board too is a good sign. I understand that you want to ensure that everything ?is setup correct before you power up everything. Thats good practice. To make things a little bit easier I would recommend to not power up everything together but do it in steps like I've done it: 1. Radudino. I first connected a USB cable to the Raduino and plugged it into a USB power adapter. Don't use the 12V power supply yet. ?You also could connect it to a PC port, but its maybe more save for a first test not to do this. You should see Version and a frequency in the LCD Display. Adjust Display contrast if necessary. 2. If this is OK, remove USB cable and connect 12V power to the Raduino 12V power(orange wire = 12V, Black = GND . Raduino should work exactly as before. 3. disconnect 12V ?power from Raduino and connect it to 12 PWR of BITX40. ?You should hear some noise in the loudspeaker, even without antenna connected To be on the save side, measure current and it should be no more than 150mA. 4. If everything looks good you could also connect Power to Raduino and you should be able to tune and here some changes in the noise, possibly some clicks while tuning and at around 7.2MHz a beep (birdie). 5 Now connecting 12V to PA-PWR. There shouldn't be a big difference in current measurement. I wouldn't press PTT at ?this stage ?because I first would check the system with a 50 Ohm Dummyload to see if ?current in transmit mode is still in range and eventually align it according to Wire Up Instructions before connecting it to a real ?tuned antenna. I don't know what test equipment you have at hand so maybe its now the time to ask for support in your local ham radio club. I'm sure that OMs there are more than willing to support you with your BITX40. ? |
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College Professor Simon Thompson
开云体育Thank you very much for the methodical approach to testing for power. I am happy to say that all connections have been made, as you suggested, and the radio is transmitting and receiving very nicely, although I will have to calibrate it, as it is a bit off frequency.
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