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QCX+ Not Transmitting
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Ron, yes, I've set the frequency to 25MHz.
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Roelof, I'll have a look at that tomorrow. I'm also going to double check my SDR is working properly at this frequency because with 13.8V appearing at the antenna it should be transmitting.
But I now realise I measured this voltage with the DVM set to DC so is it a true reading? I've ordered a better DVM which can do lower AC voltages than my cheap one can - and we will see what it shows. |
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Roelof Bakker
Hello John,
Further to the 'unstable' voltages on pin 11 of IC3, I gather this is caused by the on / off keying in rhythm of the Morse. A digital multimeter will show a kind of average. Using a VOM with a moving coil meter, slow Morse can be read from the meter movement. My own QCX+ for 40 m worked flawlessly after the build was completed and power output was 4 W at 13.8V, good enough for the time being. So no need to delve into the circuit diagram yet. Have you measured the DC voltage on the junction of C32 and L4 in straight key mode. See page 157 of the manual, with key on and off? And when you are at it also at the drains of the BS170. E.g. on the junction of C30 and C29. This way you can check contnuity of L4. 73, Roelof, pa0rdt |
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John, are you using the TCXO option on this radio? If so, did you remember to set the default 27 MHz reference frequency to 25 MHz?
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Roelof, thank you.
I've just tried that and it gives a much better result. Pin 11 with a straight key/constant send was 4.98V and the voltage at the dummy load was a constant 13.8V. I've also checked pins 12 and 13 and they are behaving correctly. 5V on receive, dropping to 0 on transmit. Sadly, having connected it to an antenna I still can't detect any signal using my SDR. John |
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Roelof Bakker
Hello John,
Have you measured the voltage at pin 11 of IC3, whilst in straight key mode, aka sending a constant carrier? 73, Roelof, pa0rdt |
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I've done a bit of fault finding this morning after taking it out of the case. There is certainly something weird happening on transmit.
Starting to work through the fault finding guide for the transmit circuit the voltages on IC3 when receiving were exactly as they should be. Things changed which I set it to transmit. As my oscilloscope hasn't arrived yet I can't check the waveforms on transmission but pin 11 was not giving the right voltage. The guide says it should be +5V but it fluctuates in time with the dots and dashes showing around 2.5, 3.5 and 4.9. It is hard to read them as they change quickly but it certainly isn't the steady 5V the guide says should be there. The supply voltage was 11.9V when on receive and this dipped to about 11.7 on transmit. As the radio is supposed to work between 7 and 16V I don't think the supply is at fault. I also measured the output voltage using the dummy load and found that was fluctuating too in time to the dots and dashes. This time the fluctuations were between 7 and 13 volts. Last night I didn't measure any voltage on the dummy load but I think that was because I put the probes on the top board, not the bottom one as the dummy load instructions say you should - RTFM! I've also checked the voltages around T1 and they were correct. So, I'm stuck. I've found something wrong - the fluctuating voltage on pin 11 of IC3, but what might cause that? As before, all suggestions will be most welcome. John |
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What is the supply voltage? You say battery pack shows a change in voltage when transmitting. The current used by the QCX during transmit is low enough that it should not impact the voltage.
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Fred, Thank you, I'm hoping it is just a dry joint. :) Roelof, I double checked, trying with the "P" visible and without. I was hoping it was just a finger problem but it seems on this occasion it isn't. On Mon, 14 Dec 2020, 20:54 Fred Spinner, <fred.spinner@...> wrote:
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Roelof Bakker
Hello John,
Have you checked that your QCX is not in practice mode? This has happened to me more than once... 73, Roelof, pa0rdt |
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So I am going to throw out the best guess here and say check the insulation on the LPF toroids and make sure that you burned all of it off on all of the toroids other than T1. The RF path sounds broken but the DC path seems okay. On receive you are routed through T1, or the BPF on that circuit. I haven't yet built one but I did study the schematic for all three variants and that sounds very possible. I don't think you did any permanent damage to anything. You are lucky. How much fun would it have been if it just worked the first time? :) On Mon, Dec 14, 2020, 1:14 PM John Laidler <rjohnlaidler@...> wrote:
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Thank you for all the replies. In no particular order I'm confident nothing is being transmitted as I can't measure any voltage at all across the dummy load and I would have expected the SDR attached to my PC to have seen something when tuned to the same frequency. All the balancing adjustments went exactly as described in the guide. But even if out I would have expected a signal to escape even if it was weak. I'll try and work back from the BNC connector as perhaps there is a break in the LPF somewhere. This might explain why current is being drawn but isn't resulting in a signal. I'll make up a new power lead with a break in it so I can measure the current. I've ordered one of the cheap oscilloscopes featured in the fault finding video and it arrives on Wednesday but I will see what I can find using a DVM first. John On Mon, 14 Dec 2020, 19:41 Shane Justice, <justshane@...> wrote:
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Shane Justice <justshane@...>
John, You didn't mention if you went through the BPF peaking, as well as the LPF adjustments. If not, you should go through those steps. If you have a power/swr meter, put that between your radio and a dummy load and see how much power your radio is developing. Let us know what you find and we can go from there. 73, Shane KE7TR Hello all, first post on here so be gentle. :) I've just completed a QCX+ today and all seemed to go well when I fired it up and carried out the balancing adjustments. Even better, when I connected it to an end fed antenna I started hearing CW transmissions and on the LCD the system was even making a reasonable attempt at decoding it - there were several callsigns clearly visible and my beginner's CW brain could even make out some of the letters on the slower transmissions. |
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It is possible you are transmitting into either a dead short, or and open connection and the finals just have not given out yet. Check around the output filter and BNC connector to make sure you have good solder joints and no shorts in that area.
-- 73, Dan - W2DLC |
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Hi John and welcome to the forum! Folk on here are very gentle so you should be ok :) 2E0THH |
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Hello all, first post on here so be gentle. :) I've just completed a QCX+ today and all seemed to go well when I fired it up and carried out the balancing adjustments. Even better, when I connected it to an end fed antenna I started hearing CW transmissions and on the LCD the system was even making a reasonable attempt at decoding it - there were several callsigns clearly visible and my beginner's CW brain could even make out some of the letters on the slower transmissions.
But the good news ends there. When I use the paddle dits and dahs are heard in the headphone but no one else is hearing them. I couldn't detect any transmission using an SDR and attaching a dummy load zero volts are measured on transmission. I've checked it isn't in practice mode. However, something is happening when I transmit because on the rechargeable battery pack I'm using to power it the leds on the pack go from 5 to 4 suggesting current is being drawn. The PA transistors look fine and no smoke was visible. :) Before I start going through Hans' very comprehensive fault finding guide can anyone suggest if there are any quick checks I can carry out? I've looked it over very closely visually but I wonder if there are any simple continuity tests I could do to see if there is a break or dry joint somewhere? John M7WIV |
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