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Power and SWR reading are wrong on upper bands.

 

Hi,

I just received my ATU-100 from Banggood and I did some testing with KX3 and a good dummy load.
First I've changed the EEPROM cell 05 to 01 (min power to 1W), and Auto tune to 0.
When I TX on 50MHz band, with 10W from KX3 on a 1.0 SWR dummy load, the ATU is showing almost 4 SWR and PWR of about 6W (this is with 0 L/C). If I tune, it will bring SWR to 1.45 on display but KX3 will show a SWR of 3.0
This will happen till freq is down to 7 MHz (see attached image)

I plan to redo the tandem match for a 1:5 ratio. The problem might be from the tandem match or from the diodes ? The marking on diodes seems to be "B66" or "866".? Should I replace also the diodes with BAT41

image.png

73,
Petronel
YO8SEP
 
Edited

Hi.
I would start to check the board for unsoldered relays pins. It looks like one coil is staying non shorted all the time.
Second, I would check all the relays are deenergized in reset mode except middle C switch relay, it should be energized.
In third I would check the power measuring on 28 MHz and if that value is wrong and less than value on 7mhz I would change the diodes .

This tuner will not work properly on 50 MHz. Too much it's own reactances.
 

Made some SWR measurements with NanoVNA. Red is with ATU powered on, Green ATU powered off.

image.png


On Fri, Aug 19, 2022 at 4:22 PM Petronel YO8SEP <yo8sep@...> wrote:
Hi,

I just received my ATU-100 from Banggood and I did some testing with KX3 and a good dummy load.
First I've changed the EEPROM cell 05 to 01 (min power to 1W), and Auto tune to 0.
When I TX on 50MHz band, with 10W from KX3 on a 1.0 SWR dummy load, the ATU is showing almost 4 SWR and PWR of about 6W (this is with 0 L/C). If I tune, it will bring SWR to 1.45 on display but KX3 will show a SWR of 3.0
This will happen till freq is down to 7 MHz (see attached image)

I plan to redo the tandem match for a 1:5 ratio. The problem might be from the tandem match or from the diodes ? The marking on diodes seems to be "B66" or "866".? Should I replace also the diodes with BAT41

image.png

73,
Petronel
YO8SEP
 

That's normal behavior. While the tuner is powered on and reseted, it compensate it's own reactances.?
 

I've changed the tandem match to 1:5 (changing also EEPROM #31) and now SWR seems a bit better (2.52 on 50Mhz and 1.74 on 28Mhz) on a 1:1 dummy load.

After diodes I get 4.66V for FWD and 1.04 for REF and after resistor divider (68k/34k) I get V_fwd=1.50V and V_rev=0.37V.

But I've noticed something strange when looking at the signals with and oscilloscope. After diodes, signal is quite clean, but after resistive bridge, at the entrance of PIC, I have some RF signal, same freq as TX and about 1Vpp. I get this "noise" on other pins (like button). Somehow RF (50Mhz) get's there but not sure how. Aren't 10pF capacitors enough to filter this ? What should I check next ??

Any ideas are more than welcome.

73
Petronel
YO8SEP
 

Hi Petronel,

The SWR you measure from the tandem match (4.66V and 1.04V) is equal to 1.5 which is? quite high for a 50 ohms dummy load. Are you sure of your dummy load ? If yes, the tandem match seems not very good and this is quite common especially at high frequencies.

Do you measure the same voltages at 1.8 or 3.5MHz ?

RF filtering needs more than 10pF. At the ADC there is no trouble to use a greater value (1nF or more).

73

³Ò¨¦°ù²¹°ù»å

?
 

Hi ³Ò¨¦°ù²¹°ù»å,

The dummy load is 1:1, measured with NanoVNA and also KX3.

At lower frequency, everything is fine, Swr close to 1.1 ,? VFwd = 5.5 and Vref close to 0. Also, no noise/RF on PIC pins

Might be the core? Seems to be Bn43-202 but you never know. I will order one and replace it. Right now I have only BN73-202 but that won't work.


73,
Petronel
 

Made some measurements today and above 21MHz I get some RF on 12V line. It is more with bigger frequency.?
Removed one filter capacitor (that comes in parallel with the coil of a relay) and I have 2Vpp on the 12V side. I get this , even without connecting ATU to power supply, without any cables. So, it doesn't cone from power supply.
RF noise seems to be more on inductors side.?
Where might come from? Relays, diodes, tandem match?
 

Hi YO8SEP
I know it has been some time
how did you get on with this, i had the same problem and it was the diodes that had been fitted had to be changed to BAT 41,
when i put this info on Davids's git hub, a few more users tried fitting the BAT41 then there tuners worked fine
Thanks Dave 2E0DMB
 

Is there a visual check to determine if I have the crap diodes? Have not even started assembling my Aliexpress kit yet. The diodes on my board are largish glass things.

Thanks
John, VK4TJ
 

Hi, John
Bat41 is existing in glass, painted blue .?

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