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Qmx + p. A.
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Hi. I've got the 50 Watts p. A. From qrp labs. It works very well on 40m. I testet it with 12v, 20 Watts, QCX + and QMX+, CW Modus. Great.
Trying it to use with the low Band qmx it doesn't work. I can switch on the PA but Wenn trying to transmit the Swr Protection stops the internal p. A of the qmx. Without the external PA, same antenna the qmx gas an output of 3watts, 10v Supply. When connecting with the p. A. And using the hardware test swr I got a swr of 5 and the protection will occur. But only using the qmx. Q. X+ and qcx+ there is no problem using the p. A.
I installed the two zener diodes for Protection of the internal p a. as mentioned for the Rev 1 and 2. Could they change the Swr?? |
Do you mean the PTT output of your QMX is working correctly? Like the 50W PA's LED turns red when your QMX transmits? Just wanted to point out that by default, PTT output is disabled. You need to enable it from the terminal application. And when PTT output is disabled, you will hit high SWR. To test if the PTT output works correctly between your QMX and the 50W PA, you can connect a dummy load to QMX's RF out and leave the RF in of the 50W PA open (or just put QMX into practice mode or test PTT only from the terminal application). Then the LED should turn red when QMX transmits.
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73 Zhenxing N6HAN |
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Hi,
connecting the antenna directly. 3W output . I get into the menu of putty and enabled the 5V for 40m. The red led will occour when transmitting. But the qmx sees a bad SWR when connecting to the P.A. When using the QMX+, same Firmware, everything works good. The only different is, that I installed zwo Zener Diodes at the Push Pull BS170 Transistors. Maybe they will cause that behavour ?
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Hello all,
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When I connect my Hardrock 50 linear amp to my QMX+, the SWR protection trips if I send a few dits. It doesn’t always trip… for example, I can send some characters for a short while and the SWR protection does not always trip immediately. The same antenna connected to the QMX+ directly, has an SWR of 1.3 and the Hardrock 50 will also show SWR of 1.3 (when it hasn’t tripped yet). What I think is happening is the SWR protection is quicker than the PIN diode switching I have in the Hardrock (yes, I have that option installed in my Hardrock).
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If Hans ever gets some free time, maybe he could allow variable timing of the of the checkpoint at which the SWR protection gets checked/triggered in the firmware. By default, Hans shows that the SWR check is very quick, which would normally be a good thing. Otherwise, it’s hard for me to test my theory. BTW, if I turn off the SWR protection, I can use the Hardrock fine and the SWR indicated on the Hardrock is fine. But the SWR protection is a great feature and I would like to keep it enables at all times.
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I don’t know if this is the same situation as the OP posted regarding the QRP Labs 50w PA.
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Cheers,
Gregg W7GRM |
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I'm seeing the same problem.
The QCX Mini works flawlessly with the QRPLabs 50W amp.
If I swap in the QMX, SWR protection trips when transmitting.
I think it is set up correctly since the red light comes on when transmitting.
Interestingly, the red light comes on even when the QMX is not really transmitting (due to SWR protection being tripped).
Was a solution to this issue ever found?
Thanks.
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73, Mike KK7ER
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Hello Mike ?
This is not necessarily an issue. Firstly, the 50W PA was designed to go with the QCX not the QMX. Using it with the QMX will work but I think you would need to switch off the SWR protection or increase?the threshold. It's been well documented that the input impedance of the 50W PA is not close to 50 ohms. Which won't cause any issue to either the QCX or QMX PA's.? The red light comes on when the QMX is not transmitting, for the same reason it will also come on when the QMX is in Practice mode (CW); the QMX is in Transmit mode (not Receive), but it is not generating any power output. So this is also correct. 73 Hans G0UPL |
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On Sat, Aug 31, 2024 at 07:34 AM, Nurlan wrote:
In Some? ICOMs? The ground is not ground but is connected from GND plane of the PCB to the case via? an inductor with fine wire windings.
IF there is appreciable RF return current to ground from the? PA? (The OP of the? PA is the worry not so much? the input ) then? this coil burns out.? You will see this effect only in the case where both the driver and the amp are not? galvanically separated in terms of PSU.? Basically no laptop 19V supply is galvanically isolated. The Destruction of this toroid / earth connection? a? known issue with? the MXP? 50? packaged? Chinese amp, which is copied under various disguies.? ?If you fully isolate the? INPUT Bnc? and wire the input? TFR of the? ?50 W amp or any other amp so that there is? ZERO ZERO galvanic connection from that winding? to anywhere but the? COax driving the transformer primary? then there is no return path for any high current RF from the driven amp back to the driver. This might involve mounting? the BNC on a polymer plate an then screwing that plate to the frame? ALSO if not blindly obvious the? GROUND connection of the BNC goes to a COPPER WIRE on the IP Transfomer.? There is NO connection from that? formerly grounded wire to the PCB, Capice ??? It's not rocket science.? ? Other methods of avoiding the big burn out with an MXP 50M involve using two sep PSUs one for the Tx and one for the? amp with no ground connection between them? but sooner or later somewhere the zero volt lines will end up connected later on and the potential H power high RF current return path will be established . Don't count on this method , you would not use it on a heart-lung machine.? TEF |
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Hans, Mike,? I have been using my QRP Labs 50 watt amp first with QDX, then QMX, and QMX+.? But with my second QMX+ I had the same results as mentioned by others- SWR protection kicks in and stops transmitting.? Checking the PTT output circuit I found only about 2.7volts out of the port to drive the amp's PTT input.? It was enough to illuminate the amps tx light, but not sufficient to control the transmit/receive circuits.? Replaced Q204? (twice!) and now get about 3.4 volts out which is enough to make the amp happy.? The QMX shows an SWR of 2.1, within the default value of 3. The underlying issue is the gate voltage to the MOSFET.? With the PTT configured as TX PTT +5? and in receive I measure the gate at ~4.95, as expected with the 100k pullup to vcc.? Using the 'P' function on the diagnostic screen the voltage drops to 3.27.? This is sufficient to get the MOSFET conducting, but not? saturated. So the question is why doesn't the gate go to zero when asserting the 'P' command?? ?The gate voltage on the other PTT output signal, RX from Q203? does transition between ~3.3 and zero as expected. Checking the my other QMX and QMX+ gives similar results, the PTT voltage is adequate but not the full ~5 volts expected. Thanks, 73 ?KG8IW Bruce ?
On Thursday, November 7, 2024 at 08:31:44 AM EST, Hans Summers <hans.summers@...> wrote:
Hello Mike ?
This is not necessarily an issue. Firstly, the 50W PA was designed to go with the QCX not the QMX. Using it with the QMX will work but I think you would need to switch off the SWR protection or increase?the threshold. It's been well documented that the input impedance of the 50W PA is not close to 50 ohms. Which won't cause any issue to either the QCX or QMX PA's.? The red light comes on when the QMX is not transmitting, for the same reason it will also come on when the QMX is in Practice mode (CW); the QMX is in Transmit mode (not Receive), but it is not generating any power output. So this is also correct. 73 Hans G0UPL |
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Interesting.? My QMX+ behaves the same way - the processor pin for some reason only pulls the Q204 gate voltage down to about 3.3V, and the source pin is at 4.9V.? This does turn on the transistor, giving a Vgs of -1.6V, which according to the data sheet is the 'typ' gate threshold voltage.? But most of the 'on' parameters in the data sheet are shown with Vgs at -3V or greater, and you can extrapolate to a high D-S resistance at -1.6V, rather than the low resistance this part is rated for.? So you are correct, Q204 is on 'barely', but not in saturation, so any load at all on the PTT line will be able to easily pull the voltage down. Stan On Wed, Nov 20, 2024 at 3:06?PM Bruce KG8IW via <b1simon=[email protected]> wrote:
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I bet the firmware has a logic 1 to PTT_P output cell instead of logic 0.
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To get pulled all the way up to 5v, the STM32F IO cell for PTT_P must be in tristate mode.
To go low, the firmware turns on the totem pole output, allowing what should be
the logic 0 to get through and driving Q102's gate to ground.
Instead it is a logic 1 going out, driving PTT_P from VDD at about 3.3v.
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Your best bet might be to somehow use PTT_N with a bit of extra circuitry
out at the amp to invert it.
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Jerry, KE7ER
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Seems like it could be a bug... I have added it to my list... 73 Hans G0UPL On Thu, Nov 21, 2024 at 5:24?AM Jerry Gaffke via <jgaffke=[email protected]> wrote:
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I'm just reviving this thread to see if others have had any further success with the 50w Amp. I went around the horn a couple times until I remembered reading something about this. I had issues with erratic, low tx out of the amp when connected to the QMX. Aftew going through one end of the amp to the other--including replacing the 4.7k POT with a multi turn variety, same results.?
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On the qcx mini, it works flawlessly as designed at about 23 watts, 13 volt supply.?
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I have re-read some of the comments here but don't quite understand the issue causing this problem; the ptt is putting the amp into transmit, 4 watts input to the amp and dummy load and Bird 25w slug...power jumps around from 10-15 watts out, but very erratic. Just curious whats going on (SWR safety is disabled)...its as though the qmx is throttling back on the input power?
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If nothing else I have re-confirmed the amp works A-OK with the qcx as designed...
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Scott vy1co |
Nurlan
Timothy Fidler
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