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Hi All,

I hope you can help me to track down problem which I have with my BPF on newly build QMX. QMX is working ok and it is transmitting 3.5-4W at 9V, I also made QSO on 40m band.

Issue I have is that I can hear only strong stations where signal on my other rig is S8 or more.

Looking at my BPF plots at terminal I can see that I have big suppression on the bands from -30db to -50dB. I think this explains why my QMX has low sensivity.

I cheked capacitors C401-404 values and location, as well as resoldered coil L401

Here are key graphs and some photos of the board.

Any pointers would be greatly appreciared.



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73 de Marek SP9TKW

Thanks Mike, I will try tonight and report.

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73 de Marek SP9TKW

Hi Mike,

unfortunately Factory Reset did not change things at all.

If I receive signal on my main rig at S7 or higher I can hear station on QMX, however if it is S3-4 there is no signal on QMX.

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73 de Marek SP9TKW

Check the voltage at C406, should be about 2.5v (other end is at ground).

-mike/w1mt

I am not sure why Mike suggested C406, but when I built my QMX, on my final inspection under a microscope I found my C406 was damaged.? I never powered up until after I replaced it.??

I had a QDX with similar poor plots traced to an issue with the T401 equivalent?

I have a similar problem Marek, TX is OK but in my case no receive at all, and all the graphs flat line.
I'll? be watching this space with interest.

Paul DJ0CU G4ADF

C406 is a quick way to check the tricolor windings. If it’s not 2.5v then likely the tricolor (maybe an IC but less likely). If it’s good then the tricolor may still be bad and that’s when I rewind it just to be sure.

Trifilar not tricolor. Autocorrect is not electronic savvy.

I wound the Trifilar using tricolors to make it easier and not having to use an ohm meter:)

A lot of left over wire from Elecraft kit building.

Voltage on C406 is 2.42V so I guess its correct. Just in case I will rewind T401 trifilar transformer in case there is a shortage inside winding.
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73 de Marek SP9TKW

You've probably already done it but I would check continuity from IC 402 pin 7 to IOC 403 pins 7 and 9. And to ground ~5k ohm

Also if one of the secondary windings is reversed it may cause the problem.

I remade T401 again and checked for continuity. I measured resistance between IC402 pin 7 and ground it is about 6kohm. I re-soldered L401.

I noticed that C410 is missing 0.1uF VCC to ground. Could this have an effect? Should I solder it in.

No change to BPF plots. I am lost at what it can be.

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73 de Marek SP9TKW

Very unlikely that missing C410, Loss of some VCC decoupling would be the problem.??

I would lift just one of the T401 secondary leads and run the plots.??

But first I would double check all solder joints under high magnification.? Should result in a gain reduction compared with normal operation and probably screw up the Diagnostic/Audio Freq Sweep.

Another debug test would be to Lift the T401 Primary and connect it to the <RXIN> that can be accessed at the intersection of C402, C402, C494 ( this could also be found as one side of C403 which is not installed)? This would bypass the BFP filters and? the plots?should be higher gain without much filtering.

I am pleaded to help.
Chris

I would say yes solder it in. Whether it makes a difference, I've seen stranger things.

-mike/w1mt

Chris and Mike

Thank you for your input, it is much appreciated. Today propagation is s**t so good time for tinkering with radio gear. I will report later on today.

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73 de Marek SP9TKW

Chris,

I think I will go for BPF bypass straight away. In this way I will confirm that this is were problem lies.

I located T401 input connection but I need to confirm <RX_IN> side. Do you mean C401-C402-C404 common point? I think there was typo in your previous post so I need be sure.

Can I shorten these two points or do I need to unsolder and disconnect T401 input side and connect to <RX_IN> using short jumper wire.

Thx.


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73 de Marek SP9TKW