[hpsdr] Help with Alex SWR

[dlwaddel at netzero.net]

Thanks, everyone, for the helpful suggestions. Here are some of them and my responses.

"It sounds like you are fighting several problems."

*** No doubt about it! 

"Apparently you are trying to build an Alex from a bare board?"

*** Yes, from a bare PC board. That is most of the fun!

"You seem to be having problems with both the low pass filters on 10 and 6
as well as the directional coupler."

*** Amen, brother, my thoughts exactly. I'm most interested in the directional coupler problem first.

"For the purposes of all toroid windings, the definition of a "turn" is one pass through the center of the toroid.  Any pass through the center hole is a turn. Are your turn counts correct?"

*** Got it. Counting turns is how I found the wrong cores on the directional coupler. I also found an incorrect core in the 6 meter filter and fixed that. I found one core in the 10 Meter filter with one turn short. Counting the turns inside the core gives the correct count or counting the turns on the outside and adding 1 gives the actual count. See, been ther, messed up there. :)

"Do you have, or have access to, an antenna analyzer, like the MFJ-259 or similar/equivalent?"

*** No. I'm beginning to look for a project to build one, but no luck yet. I might find one at the next hamfest I attend - Lawrenceville, GA.

"Did you use the exact part number for the detector diodes (D1 and D2), or substitute something else?"

*** Exact, right from the BOM - Mouser 621-1N5711W-F

"Did you use the exact part number for the 50 Ohm (actually 51.1 Ohm) resistors for the power bridge(R2 and R3)?
... or substitute something else?"

*** Exact part. The resistors are stamped "51R1" right on them. 

"Where did you get your toroids?  Are you using genuine MicroMetals and FairRite toroids, or did you substitute something else? Or get a set of the Chinese toroids from TAPR?"

*** The cores for the directional coupler are Amidon FT-50-43. The others came from Parts and Kits and I don't have a clue what brand. The "Black" cores are supposed to be FT50-10. They are black, but seem to have a brownish color painted on one side. I have to check back with Parts and Kits about them. I wonder if the Amidon cores are different from the MicroMetals or FairRite cores with the same part number.....

"What gauge wire did you use to wind your 10 Meter toroids?"

*** 22 AWG

"... your 6 Meter toroids?"

*** 22 AWG
"... your directional coupler toroid windings"

*** 22 AWG for the multi-turn windings

"... your directional coupler "staples" (single through toroid jumpers)?"

*** 18 AWG teflon covered. Tried both stranded and solid.


"Make sure that the control wiring to alex did not get disturbed or pluged in wrong as recheck externalconrtol is turned on and correct"

*** Checked several times. I can hear the relays click when changing bands and when switching the transmitter on or off.

"T1 and T2 fors the directional coupler for sampling the reflected current.

If the winding directions are wrong, you could be reversing the forward and reversed 
currents, and therefore cause a large measured SWR even when the actual SWR is low.

I would very carefully inspect the winding directions again (those open dots)."

*** Checked several times. The cores don't fit well if the windings are not according the the winding convention for the rest of the toroids. I intend to try reversing T2 to see what happens.

" did you calibrate the watt meter via the setup form in PowerSDR - see HPSDR Setup, PA Settings, Watt Meter.  Calibration steps are presented on the form."

*** Have not tried that. Will look into it and give a try. Before I changed T1 and T2 to the correct cores, and even now on the low bands, the power displayed in HPSDR is close to what my external meter says. SWR is way off on all bands.  I would expect, from the voltage readings on jack J2 that the directional coupler is the issue, or that there really is an SWR issue between the directional coupler and the cable to the external power/SWR meter and dummy load.. However, I sure don't see what is causing it. The cable has to be good, since I use the same cable when bypassing Alex.

Don
K3DLW
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