Hermes Homebrew Fault Finding

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Prem
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Re: Hermes Homebrew Fault Finding

Postby Prem » Fri Oct 13, 2017 3:18 pm

Hi Scott

What can be the minimum spec for a descent scope to buy which can cover all Hermes signal tracing ?
Which is the first point we expect a sine wave ? Is it at it at DAV ouput or T1 primary ?

Pine1 was at 1Mhz, 2 at 2 plus and so on itwas different.
Do you expect a faulty DAC IC ?

Rds. Prem
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Fri Oct 13, 2017 5:10 pm

I do not believe you will need a better oscilloscope to solve this problem. However, the highest frequency on the board is 125MHz.

The first place you will see a sine wave is at the DAC outputs.

Again, have you checked transformer T1 at the output of the DAC and its surrounding components?
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Re: Hermes Homebrew Fault Finding

Postby Prem » Fri Oct 13, 2017 5:41 pm

Hi Scott,

Connection around T1 sound good. Out from DAC is directly going to T1 primary and there 51Ohm resistor also connected .
Since DAC is generating Sine wave out and we find it is not happening !
In this case will T1 and rest of components will help us ?

Do you expect FPGA possible fault ? Else shall we try a replacement of DAC ?

Voltage at Pin 17 of DAC vary from 200 mV to 1.7 with drive change.
almost same voltage change at U3 Pin-3 also seen.

73s

Prem, A65BK.
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Fri Oct 13, 2017 7:52 pm

Prem,

I'm sorry, but at this point I don't know what to suggest next.

There are people who don't use the forum on both the Apache Yahoo Group, and the HPSDR mailing list. Perhaps if you post the photo of DAC output at 1MHz someone there may know exactly what is going wrong.

73,

Scott
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Re: Hermes Homebrew Fault Finding

Postby Prem » Sat Oct 14, 2017 2:15 am

Hi Scott,
It is quite unfortunate that none else is joining the forum discussions.
Finally at this stage I would request you again to help me to trace out why I get a FWD power S meter and RF power out even if I have not plugged a mic ? May be we can reach somewhere to a solution than going behind waveforms which we are struck in between.

Without Mic plugged and so no audio, how PSDR generate RF out iwhen MOX pressed. Since you know very well what is the process being happening inside, you can very much support me further to do some more trouble shooting.

Also I request other team members to flash some light into this discussion. Please share your thoughts even if not fully confident on the statement !
I double people are scared to put some statement or opinion against or different to ongoing discussions !!

Please support with your valuable advices.

" what can be the reason for me to get RF out even without my mic plugged in" This RF will vary with my drive as well as Mic gain. If I disable min, this RF power is not there !

Please note that this S meter reading is not a false reading. I get this RF power out in external meter. Also current consumption also in agreement with S meter reading. Means this is not a false reading at all , Threr is RF being output from final Ant jack!

Awaiting your valuable suggestions and advices.

73s

Prem, A65BK.
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Sat Oct 14, 2017 4:02 am

The normal noise level out of the CODEC with no microphone plugged in is -70dB. This is normally not enough to generate any substantive amount of RF output. However, since your DAC is generating an aberrant waveform, you see a substantial amount of RF when any amount of drive or noise is present, even a tiny bit.

73,

Scott
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Re: Hermes Homebrew Fault Finding

Postby Prem » Sat Oct 14, 2017 4:18 am

Hi Scott,

So shall I do focus my further checking to FPGA and DAC ? Until we get a Sine wave at DAC out, we need not further investigate further stages beyond T1. Is it ?
I have measured the signals at 20m and looks as if it is better than 1MHz. Please have a look into my below video post.

http://www.youtube.com/watch?v=CcRBmxd_yqg

Rds, Prem A65BK
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Sat Oct 14, 2017 11:42 am

As soon as you get a good sine wave from the DAC everything else will be perfect and there will be nothing else to investigate.

It does not look better at 20MHz, your scope is merely undersampling the waveform.
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Re: Hermes Homebrew Fault Finding

Postby Prem » Sat Oct 14, 2017 3:38 pm

Hi Friends,

Now I connected my Hermes plus my 10W drive amp and work FT8 mode using WSJTX. I could work few stations.
But still I could not resolve issue with SSB signal error. I work on 20m now.

73s

Prem, A65BK
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Re: Hermes Homebrew Fault Finding

Postby Prem » Wed Oct 18, 2017 4:09 am

Hi Phil,

Please have a look at the Two tone test screen shots with and without DUP on.

73s,

Prem, A65BK
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Wed Oct 18, 2017 11:11 am

Still looks broken. Exhausted my ability to figure out what that is, though. Still something to do with the FPGA/DAC.
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Re: Hermes Homebrew Fault Finding

Postby Prem » Wed Oct 18, 2017 2:10 pm

Hi

Can we conclude fault to foga or dac ?
Anything else to check ?

If nothing else can be the reason, we will try replace fpga. But how to remove it another nightmare for me

Rds

Prem
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Re: Hermes Homebrew Fault Finding

Postby Prem » Sat Oct 21, 2017 6:46 am

Hi Scott,

I have monitored the DAC IC Data in pins from 1 to 14 and slide show video captured as below.

I have viewed waveforms on all DAC IC data pins from 1 to 14 and result captures as a slide show video as below.

http://www.youtube.com/watch?v=zD-YrjdBSKA


Rds,
Prem, A65BK
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Sat Oct 21, 2017 11:26 am

Prem,

Good effort, and the idea of looking at the data on those pins to isolate the problem to the FGPA or DAC is a good one, however you don't have the right equipment to do it. First, your scope is too slow to resolve the 125MHz data rate, that is why the signals become unreadable after you get past pins 2 and 3. Second, even if you had a fast enough scope, what you really need is a 14 bit logic analyzer that can read the data and plot it out for you.

So, unfortunately, it is impossible to know if the data is correct from your video slide show.

73,

Scott
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Re: Hermes Homebrew Fault Finding

Postby Prem » Sat Oct 21, 2017 12:25 pm

Hi Scott,

What you expect ? the fault in FPGA or DAC ?

Rds, Prem
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Sat Oct 21, 2017 3:19 pm

Prem,

I'm sorry, I have no way to know.

73,

Scott
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Re: Hermes Homebrew Fault Finding

Postby Prem » Thu Nov 02, 2017 12:54 pm

Hi Scott,

Today I replaced DAC IC U5 with new one. So happy to see that all my issued got resolved . Now

_ No faulty RF out during MOX with MIC plugged and not modulating
_ I get Sine wave at DAC out measured at T1 input
_ Finally I measure Sinewave at RF ant out during Tune even at higher band (20m band) in my 20MHz scope.
_ During Sb Tx I get a varying clean waveform at my Ant port.

So I presume my Hermes almost ok now.
Next will test the SSB signal quality in a local receiver and then finally on air with other stations.

Thank you very much for continuous support and advice's.

73s

Prem, A65BK.
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Hermes Tune Waveform .JPG
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Thu Nov 02, 2017 2:38 pm

Great news, Prem! :) Smart of you to swap the easier/cheaper IC first ;)

73!

Scott
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Re: Hermes Homebrew Fault Finding

Postby Prem » Fri Nov 10, 2017 6:50 am

Hi Scott,

Please have a look into the PSDR display during Tune and MOX - SSB. Is this normal or else any issue ?
Why I am asking is by seeing the spreaded waterfall during SSB mode TX !
Is thsi normal ?
I had connected my Hermes 5-10W driver PA to a dummy load during this test.

http://www.youtube.com/watch?v=JzdXv26hWl8

Alsohave a look at the screen shots with
1. Driver PA out with Tine on 40 m Band. PA connected to dummy load. My Driver PA use 2 nos IRF530 Mosfet in Pushpull. As per vendor recommentation Gate bias set at 2.7V. PA powered from 13.8V.
2. PA in signal
3. PA in signal when PA power is disconnected.

So I can see when PA is powered ON , the sine wave loose shape as seen. Is it normal or else some issue with PA ?
My PA as below

https://www.ebay.co.uk/itm/DIY-kits-70W ... SwdDBZgbmL


73s
Prem
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PA OUT.JPG
PA OUT.JPG (95.8 KiB) Viewed 4140 times
PA IN with PA Power OFF .JPG
PA IN with PA Power OFF .JPG (89.46 KiB) Viewed 4140 times
PA IN .JPG
PA IN .JPG (84.25 KiB) Viewed 4140 times
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Fri Nov 10, 2017 2:57 pm

Why your display looks the way it does and how to adjust it:

https://apache-labs.com/community/viewtopic.php?f=6&t=2545

Your amplifier looks broken to me. I've never built one myself so I am not equipped to debug it. However, if I had to guess, it looks like there is an impedance mismatch on the input, and that you are over driving the hell out of it. What happens if you put a 3 or 6 dB attenuator in between the Hermes and the amp?
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Re: Hermes Homebrew Fault Finding

Postby Prem » Fri Nov 10, 2017 4:00 pm

Hi Scott,

As per description given vy vendor this amp is designed to deliver 70W with an input max 5 watts !

So our hermes can over drive it ?

73s

Prem
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Re: Hermes Homebrew Fault Finding

Postby w-u-2-o » Fri Nov 10, 2017 5:45 pm

Prem,

I don't know. It's just a wild guess from looking at the waveform.

I'm sorry that I have no experience with these amplifier kits.

Scott

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