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QMX SWR meter gone mad (SOLVED)

 

Hello, Adrian, thanks for the link!
I checked the windings. They look the same as in NorCal power SWR meter as well as the photo in assembly manual.
So then the only other possibility was that one end of one of the 10-turn windings, the ground connection, had no contact. When I looked in the schematic diagram, this seems to be the only possibiity, because then all continuity testing goes through other windings and there is apparent break in any of the windings.?
I gave all solder points some more heat, for the 10-turn windings I added a micro droplet of solder and heated the hole until I noticed that the solder was sucked in - this means that the enamel insulation has burned and the "naked" copper surface accepted the solder.
And voil¨¢ - dummy load shows SWR almost 1 (it gets worse towards higher frequencies, but still shows something about 1.17 at 14 MHz).
Uff, I am so happy :-D

73 + HNY de Jindra


On Mon, Jan 1, 2024 at 11:10 AM, Adrian YO3GFH wrote:
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
 

P.S. now I realized that in Power/SWR display the TOP bar is power and the BOTTOM bar is SWR (BTW I think this is not explained in Operation manual). With my SWR transformer screwed the top bar was very small (1-3 pixels wide in the first rectangle) while the bottom was showing "full throttle" - it was the SWR! Now it is exactly opposite: top shows full output, bottom remains empty when transmitting into dummy load.


On Mon, Jan 1, 2024 at 11:56 AM, ok4rm wrote:
Hello, Adrian, thanks for the link!
I checked the windings. They look the same as in NorCal power SWR meter as well as the photo in assembly manual.
So then the only other possibility was that one end of one of the 10-turn windings, the ground connection, had no contact. When I looked in the schematic diagram, this seems to be the only possibiity, because then all continuity testing goes through other windings and there is apparent break in any of the windings.?
I gave all solder points some more heat, for the 10-turn windings I added a micro droplet of solder and heated the hole until I noticed that the solder was sucked in - this means that the enamel insulation has burned and the "naked" copper surface accepted the solder.
And voil¨¢ - dummy load shows SWR almost 1 (it gets worse towards higher frequencies, but still shows something about 1.17 at 14 MHz).
Uff, I am so happy :-D

73 + HNY de Jindra

On Mon, Jan 1, 2024 at 11:10 AM, Adrian YO3GFH wrote:
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
 

Good to hear it's working!
Having a slightly higher SWR on 20m is normal, try moving the 10 turn windings as far as possible from the 1 turn ones, it should improve it a bit. In my case, I couldn't make it go lower than 1.12.

73,
YO3GFH
op. Adrian
 

I replaced the diodes in the SWR bridge with a matched pair of 1N5711 hot carrier diodes and now I have SWR readings that are essentially 1:1 on all bands.
The supplied rectifier type diodes have way too much reverse capacitance and are unsuitable for RF.?
 

That is great. My SWR bounces around and sometimes shuts down the xmtr. I am ordering the diodes now. Thanks for the great tip.?

Mike Krieger WA8UOC


On Tue, Jan 2, 2024 at 1:04?PM Randy Ott <k5hj@...> wrote:
I replaced the diodes in the SWR bridge with a matched pair of 1N5711 hot carrier diodes and now I have SWR readings that are essentially 1:1 on all bands.
The supplied rectifier type diodes have way too much reverse capacitance and are unsuitable for RF.?

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