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Jim,

Thanks for your advice. I decide to leave it there for now. I might try the adding capacitor method when I feel it's necessary.

73 de Lun BD8BTE

Ahoj!

I found a bit clearer description of the SWR bridge winding process in the Norcal powermeter assembly manual, page 10:



You should also check if the 1 turn windings are as far as possible away from the 10 turn ones.
Hope it helps!

HNY!
YO3GFH
op. Adrian

I checked continuity and all four connections are OK.?
So when I look at the schematic the most likely error is 10-turn winding orientation (A-A and D-D). The assembly manual does not specify winding orientation and honestly, I was not sure which direction is right. That could probably explain "infinite SWR" when connected to the dummy load.
OTOH why it shows more or less reasonable SWR with real antenna is a mystery...
73 Jindra

Here's a description with image of how I installed Zener diodes on my two QDX'es. The minus goes to the Drain and the plus end of the Zener goes to ground.?

73

--
Sverre

LA3ZA
http://la3za.blogspot.com

Hello,
my self-built low-band QMX works fine with EFHW antenna on 40 and 20 meters. It usually switches on SWR protection on 80 meters.
I measured the actual SWR performance of the antenna at the connector in ham shack by VNa and got this:

80 m: SWR < 3 at frequencies above 3535, dip at 3684 (1.07)
40 m: SWR < 2 everywhere in the band, with a dip at 6844 (1.43)
20 m: SWR <1.8 under 14100, <2 in the whole band, dip at 13749 (1.36)
SWR protection seems to be working accordingly, except some glitches at 40 and 20 meters when it occasionally blocks TX without apparent reason.

However, I am shocked when see results of SWR sweep:
20M:

10 |.? ?***.? ? ?.***? ?.***? ? ? .? ? ? *|? **? .? ? ?*.? **50%*

? ?|.? ?*? *? ? ?*? ?*? .*? ? ?.? ? ?.*? ? ?.? ? ? *? ? ?*? **? .? ? ?*.? *? .

9.0|.. .*. * . . * . * .*. . . . . . .*. . ... . . * . . * * * ... . .*. .*. . .

? ?|.? ?*? *? ? ?*? ?*? *? ? ? .? ? ?. *? ? .? ? ? *? ? ?* * *? .? ? ?*.? *? .

8.0|.. * . .*. . * . .*.*. . . . . . . * . ... . . * . . |** * ... . .*. * . . .

? ?|.? *? ?.*? ?*.? ? **.? ? ? .? ? ?. *? ? .? ? ?*.? ? ?|** *? .? ? **. *? ?.

7.0|.. * . .*. .*. . .**.. . . . . . . .*. ... . .*. . . |*. .*... . * * * . . .

? ?|.? *? ?.*? ?*.? ? **.? ? ? .? ? ?.? *? ?.? ? ?*.? ? ?|*? ?* .? ? * * *? ?.

? ?|.? *? ?. *? *.? ? ? .? ? ? .? ? ?.? *? ?.? ? ?*.? ? ?|? ? * .? ? * * *? ?.

6.0|..*. . . * .*. . . ... . . . . . . . * ... . .*. . . | . .*... . * **. . . .

? ?|* *? ? . *? *.? ? ? .? ? ? .? ? ?.? ?*? .? ? ?*.? ? ?|? ? * .? ? * **? ? .

5.0|*.*. . . .** . . . ... . . . . . . . * ... . .*. . . | . .*... . * **. . . .

? ?|.*? ? ?.? ** .? ? ? .? ? ? .? ? ?.? ? * .? ? ?*.? ? ?|? ? * .? ?*? *? ? ?.

4.0|.* . . . . . . . . ... . . . . . . . . *.. . .*. . . | . .*... .*. . . . . .

? ?|.*? ? ?.? ? ?.? ? ? .? ? ? .? ? ?.? ? ?*.? ? * .? ? ?|? ? ?*.? ?*? .? ? ?.

? ?|.? ? ? .? ? ?.? ? ? .? ? ? .? ? ?.? ? ? *? ? * .? ? ?|? ? ?*.? *? ?.? ? ?.

3.0|.. . . . . . . . . ... . . . . . . . . ..* . * . . . | . . *.. * . . . . . .

? ?|.? ? ? .? ? ?.? ? ? .? ? ? .? ? ?.? ? ? . *? * .? ? ?|? ? ?*. *? ? .? ? ?.

2.0|.. . . . . . . . . ... . . . . . . . . ... **. . . . | . . .***. . . . . . .

? ?|.? ? ? .? ? ?.? ? ? .? ? ? .? ? ?.? ? ? .? ? ? .? ? ?|? ? ? .? ? ? .? ? ?.

1.0|.? ? ? .? ? ?.? ? ? .? ? ? .? ? ?.? ? ? .? ? ? .? ? ?|? ? ? .? ? ? .? ? ?.

? ? ----------------------------------------------------------------------------

? ? 6? ? ? 7? ? ?8? ? ? 9? ? ?10? ? 11? ? ?12? ? ?13? ? 14? ? ?15? ? ?16? ? 17

?

Sorry, I sent this before reading the earlier message saying much the same…

Could it be ESD perhaps?
I always use a static grounding wrist strap.

Peter,

It is an indication that the waveform is at half the 3.3-volt supply.? It could be a constant voltage or any waveform that has 1.65 volts on average.? The only way to be sure is to verify a decent 50% duty cycle squarewave with 3.3-volt peaks.

73
Evan
AC9TU

It definitely looks like the regulator? went out. there is a bulge on the input side. As Bruce noted I am lucky the ground didn't burn as that probably would have sent? supply voltage to my brand new clock .

I see little lm317 regulators already on a board on amazon for a few bucks but wonder if a buck converter would be a better choice.??

while running this clock? on a little 5v wall wart in the shack is just good enough, I just think it would be great to be able? run the clock on emergency power (aka 12v).?
--
regards,
Bryan, N0LUF

Agree with GM0EUL, it is an analog filter with skirts (IIRC) of ?-12 dB/octave, so a signal 350 Hz higher or lower would be only 12db quieter, and therefore adjacent strong signals will still be very audible.?

Well, today I was getting started with the build and discovered that I also have the Q103 short.
I don't have a heat gun, so I'll try removing it, cleaning up a bit and reinstall the Q103 as you suggest.
Wish me luck.
Thanks for the tip!!
Glad I checked this before starting the initial build steps, just incase I mess up the Q103 fix....
Cheers,
KO4EOD

Hi Mac
Are you sure there's something wrong with it? In my experience the CW filter on a QCX is very soft compared to my K2 and KX3.? The QMX sounds steeper but still soft compared to a crystal roofing filter and dsp.? What are you comparing it to, are you used to a really tight, steep filter?

HNY and 73

Peter, GM0EUL

Greetings all,

?? ?Due to the fact that the PCB pads for the PA pins on my High-Band QDX are not as sturdy as the rest of the PCB pads (I’ve no idea why) and, indeed, one pad has broken off entirely, I have decided to install sockets for the BS170s, as I’m already going to have to do point-to-point wiring for the gate connection for one pair of BS170s and I’d estimate that if I had to change out the finals once more time, I’d have to make more than one point-to-point connection :-\ My questions regarding socketing the finals are...

1) I’m currently planning on using these () sockets. Am I going down the correct path or should I choose something else?

2) For the heat-sink, I believe that I’ve seen someone take a Raspberry Pi CPU heat-sink (or the like), drill a hole in the middle of it, and then, bending the BS170s over against it, just use a longer bolt to secure the washer into place. I know that I’d want to keep the length of the BS170 leads short (for electrical reasons) and then I’d want to invert the heat-sink, so as to let the BS170s be able to press down against a flat surface. Is that a viable method (if so, any pitfalls to watch out for?) or should I do something else?

?? ?For SWR protection, I also plan on installing a 1N4148 diode across L14. For those who have done this, what is the best method by which to wire it in? Also, which end does the anode need to connect to? Additionally, I’m going to install a pair of 1N4756 Zeners on the finals. Just to be certain, to which PA pins do I need to connect which Zener pins to? I’ve searched past posts in the forum, but am still unsure of a definitive answer. Finally, particularly b/c I’ve read of people using 56V Zeners (vs 47V ones), for both the Zeners and the L14 diode, do I have the correct part numbers? If not, what should I use?

?? ?I appreciate the help!

Charles Johnson
KF4AYT

Hi Charles,

There are many reasons for the discrepancy in the SWR measurements.? Since the QRPGuys meter is a kit, there may be differences in construction around the directional coupler.? My unit has tracked very well with my nanoVNA when both are used correctly.? I tested with 1% resistors for SWR accuracy.

I use the meter mainly to monitor the signal between one of my QRP rigs and a WA2EBY amp.? I then know the input and output of the amp as I have a 100-watt SWR/Power meter between the amp and the antenna.

I believe your current readings while receiving are in error.? If you rely on the current reading of a DC-DC converter between the shack supply and the QDX, you can get bypassed current through the antenna or other ground lead back to the device providing power to the DC-DC converter.

Did you have the high-impedance probes connected to the BNC T?? I do not know what a 50-ohm cable directly connected to the oscilloscope will do to SWR/reflections.? A length of cable with a high impedance (open) on the end can cause reflections.? Using the QRP-Labs dummy load with the high-impedance probe of the oscilloscope connected to the resistors of the dummy load (not the diode output) should be the most accurate.??

The above are suggestions on my part.? I may not fully understand what you are telling me, so there is a lot of room for error on my part.

Have fun hunting down the problem, and have a Happy New Year!
73
Evan
AC9TU

Hello Paul,
I don’t know. ?ESD maybe? ? I work on a grounded mat but I don’t always wear the arm band.?

Thanks for the comment,
Ken

Hi Peter,

I see three possibilities for the input imbalance:
1 - A failed gate in IC5 is pulling the output of IC11 (the Si5351a) down
2 - IC4 is pulling the output of IC11 down
3 - IC11 is damaged

The most likely is IC5 pulling IC11 down.? This can be checked when you go to replace IC5.? After removal and before installing the new IC, verify that the input pads for IC5 have good signals.? This is best done with an oscilloscope.??

73
Evan
AC9TU

Evan,

The data tells me that the antenna's impedance, as the QDX shows, is something other than 50 resistive.? That would give higher readings than a true 50-ohm resistive load would.?

While I could have used my 20W QRP Labs Dummy Load, since I was also checking the output of the 40m and 20m 50W PAs that I've built, I was using a 50W dummy load that I purchased off of Amazon () as the load. According to my NanoVNA, from 80m through 15m, the impedance was between 47 and 48 Ohms, so while it's not the 50-ohm load that I used for the power calculations, it's not the varying load that an antenna can produce :-) As for the testing setup, it was QDX --> 3-ft RG_58 jumper --> BNC T-adapter --> BNC-to-SO-239 adapter --> dummy load. I picked off the signal that fed my Siglent o'scope from the BNC T-adapter.

Also, note that SWR meters are unreliable at QRP levels if designed to handle 100 watts unless there is a low power setting.

When taking SWR measurements of an antenna, I use my NanoVNA.

If you do not have a QRP dummy load and power meter, I would suggest this kit from QRPGuys:

I have one of those :-) I don't use it all that much b/c I have not been able to get a good case for it yet, but I do sometimes use it to look at the RF power output. I question the SWR reading, though, as it often gives a reading of 1:1 when I know that the SWR (according to my NanoVNA) is above 1.5:1...

**

Evan et al,

I pulled the finals on my High-Band QDX and it is now drawing 150 mA of current in receive mode, as expected. I haven't been able to test out the finals, but from looking at the gate voltages (both with a DMM and an o'scope), IC5 appears to be intact. This brings up the question of why the unit was previously drawing only about 80 mA in receive mode. Thoughts?

Regards,

Charles Johnson
KF4AYT