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Is it really working completely? #atu-100

 

Hi
I built up an ATU-100. In general it seems to work. To learn more about it, I put a 50 ohm termination on the RF out port and put my NanoVNA on the RF Input and put the atu in test mode. I also simply put the components into SinSmith. I sequenced the inductance step wise up the range of values, setting SimSmith, and watching the NanoVna output. The inductance values agreed reasonably well with SimSmith until I got to 6.70 uh. The value on the nanovna was close at 6.33 uh at around 5.80 uh. I seemed when the inductance was 0 uh that I had about 40 nh of stray inductance. In any case, when i stepped to 6.7 uh the inductance value suddenly falls by 3 uh down to 3.70 uh on the nanoVNA and then as I step higher it continues to go lower. Eventually at about 8 uh reading roughly 0 uh of inductance. It seems to me this is not right and would cause the tuning algorithm to not work properly. I did check that the correct relays get powered on. The problem seems to occur when the 4.4Uh and the 2.2 uh inductors come on together and the others off. Clearly the inductors are approximately correct because when I track the values they are fine all the way up the scale to this point. So the question:

Am I doing something wrong measuring this way? SimSmith reports the reactance value should keep rising, although the SWR is very high at this point and perhaps that makes the measurement invalid? Is it working as expected or is there something wrong? What could it be?

The capacitance side seems to work correctly and tracks SimSmith well so I think this side is fine?

Does anyone have a suggestion about what is going on?

John
 

I think it can be explained by loss in the inductors? If the cores are low Q than the measurements will reflect that. Best regards Onno

Op za 27 nov. 2021 23:48 schreef john_mellars via <john_mellars=[email protected]>:

Hi
I built up an ATU-100. In general it seems to work. To learn more about it, I put a 50 ohm termination on the RF out port and put my NanoVNA on the RF Input and put the atu in test mode. I also simply put the components into SinSmith. I sequenced the inductance step wise up the range of values, setting SimSmith, and watching the NanoVna output. The inductance values agreed reasonably well with SimSmith until I got to 6.70 uh. The value on the nanovna was close at 6.33 uh at around 5.80 uh. I seemed when the inductance was 0 uh that I had about 40 nh of stray inductance. In any case, when i stepped to 6.7 uh the inductance value suddenly falls by 3 uh down to 3.70 uh on the nanoVNA and then as I step higher it continues to go lower. Eventually at about 8 uh reading roughly 0 uh of inductance. It seems to me this is not right and would cause the tuning algorithm to not work properly. I did check that the correct relays get powered on. The problem seems to occur when the 4.4Uh and the 2.2 uh inductors come on together and the others off. Clearly the inductors are approximately correct because when I track the values they are fine all the way up the scale to this point. So the question:

Am I doing something wrong measuring this way? SimSmith reports the reactance value should keep rising, although the SWR is very high at this point and perhaps that makes the measurement invalid? Is it working as expected or is there something wrong? What could it be?

The capacitance side seems to work correctly and tracks SimSmith well so I think this side is fine?

Does anyone have a suggestion about what is going on?

John

 

Hi, John
First of all check with a multimeter that all relays switched correctly.
And check also carefully a soldering for PIC nodes and 2n7002.
g4edg
 

Hi John

I had a similar problem on the capacitor side of the tuner. I used my NanoVNA on SWR mode and stepped through the entire capacitance range using the test mode, this isn't measuring anything in particular but you will see if the expected result of a step is proportionate and in the right direction, this revealed several "holes" in the range. This was due to the following faults

1. Cracked and open circuit?
2. Relay not operating due to faulty driver FET
3. A plated through hole that was faulty.

With the inductors it's difficult to see if they are being shorted when they should be bypassed DC wise. I took out all the inductors (and cleaned off a bit more enamel) and checked out all the relays, then replaced the inductors.

Good luck, you've just got to be mehodical.

73 Steve G4EDG
 

Thanks for the reply. Yes I checked those items and I even changed a relay to be sure. AFter the first comment and more thinking and research, I now think it is the last two toroids or at least one of them that begins to look capacitive at some point. This might be due to poor core material and it does not work as the original spec says. This was a clone and I do not know anything about the toroids and since most manufacturers have their own recipe it could be that this one is not good. I suspect a step might be to get the amidon cores and remake the toroids and see it their is a difference in their performance. This time around I will measure them before I install them and see what I can learn.

john

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