QCX and peaking BPF


Daniel Urbach
 

I have been searching an reading as much on this top as I can find and it seems that A: I need a dummy load and B: no one else is having the same issues I am.   My trouble seems to be that my peak occurs at a scale reading of 04 with the cap pretty well centered. This seems rather low compared to what others are getting.  Any ideas on what I should be looking at ? (double and tripple checked xformer phase and solder joints ) ...also has anyone else noted that the board is a bit "microphonic" ...in that moving the board about on the bench produces sounds in the headphones ?


Steve
 

Just to be clear, you want to disconnect the dummy load or antenna during alignment. Otherwise the peak BPF reading will be low. 

 

Steve N4IAG


Daniel Urbach
 

It is ...however some of the other posts concerning this are saying that is not the case .....but either way I don't have a dummy load and the antenna has never been hooked up ...neither has the key ....to keep me from transmitting until I can get the antenna hooked up.


Liam Kingsmill <lumetters1@...>
 

Daniel, I've noticed the microphonics you describe below. Tapping different places on the PCB seemed to narrow the most microphonic to the area around IC9 and IC10.

But, other issues were solved by Canada Glen who designed a workaround allowing the receiver to work quite close to what we believe was Hans' design goal.  The workaround bypasses half of IC9.

The oddest issue remains:  Starting the QCX requires a certain power switch contact bounce.  To get the QCX working can require between 1 and 20 power OFF/ON's.

That odd behavior has been mentioned by me twice before in posts here.  Since there have been no comments, it appears the issue is peculiar to # 3171.

Thank you, Glen.  Without your input I'd own a dud.

Liam

On 04/02/2018 07:01 PM, Daniel Urbach wrote:
has anyone else noted that the board is a bit "microphonic" ...in that moving the board about on the bench produces sounds in the headphones ?


Jess Gypin <ontarget1911@...>
 

What he said 

On Apr 2, 2018, at 6:26 PM, Steve via Groups.Io <senglish222@...> wrote:

Just to be clear, you want to disconnect the dummy load or antenna during alignment. Otherwise the peak BPF reading will be low. 

 

Steve N4IAG


Daniel Urbach
 

No one else has had low readings on the bpd peaking step? ...begining to make me think I have something seriously wrong.


lajes67
 

I had problems with my second kit, I couldn.t make any adjustment on the last 2 adjustment steps, turns out R27 was defective, when I plugged in the headphones and turned R27 I either had tone or didn't, checking R27 with a DVM I saw the resistance start out at 1 ohm and then the resistance would jump to 100 ohms and the higher, there was no gradual increase, I was lucky that I already had a working QCX and I was able to verify on that R27 as to what the problem was, as soon as I changed R27 I was able to proceed with the adjustments, hope this helps.

73 John K2IZ


Alan de G1FXB
 

Anybody effected,
see if this helps?

https://groups.io/g/QRPLabs/message/22418

I suspect Han's has being sidetracked to have rewritten that section into the build manuals so far.
(Listen to any subsequent advice provided.)

Either now by default, or if experiencing difficulty in obtaining a good peak. Utilise a 50 Ohm termination to the Antenna input and retry?
Expect the peak value to be lower than being unterminated, but it should peak?

Examples of expected signal amplitudes are given on the trouble shooting web page.
Other things to suspect are:-
Bare in mind the warning in the build manual, C1 Trimmer polythene dielectric is easily damaged by excess heat during assembly.
The build manual describes you may observe more than one increase in the BPF response, but only one should have true peak.
One QCX 20 builder had Low BPF peak / sensitivity & Low TX power out and found the common cause was an excessive loss through the shared LPF section.
Incorrect  insertion / damaged / defective components away from the the BPF, can also give rise to low peak values, as proven by other builds documented.

Alan


On 03/04/2018 01:26, Steve via Groups.Io wrote:
Just to be clear, you want to disconnect the dummy load or antenna during alignment. Otherwise the peak BPF reading will be low. 

 

Steve N4IAG



rentwist@...
 

Liam,

You need to do the start-up mod if your board rev is 1 or 2 (number on lower right of board).  http://qrp-labs.com/qcx/qcxmods.html#pwrup

BTW, there are a number (4 at least that I recall) recommended mods for any PCB prior to rev 3.

Hope this helps (think it will).

73,

Robert, WA2T


Denis F6GKQ
 

Hi Daniel,

First, you don't tell us which band is your QCX... Please, confirm : 40, 20, other ?

Look at Alan message https://groups.io/g/QRPLabs/message/23136, he gave you valuable informations.

I had the missing peak problem on my QCX 40m. I solved it two ways :
1) putting a 50 ohms (my dummy load but you can take any 47, 51, 56 ohms resistor you have in your junk box) across the antenna input. At this stage, I started getting a peak that I couldn't get with the antenna plug leaved open.
2) I improved the level at the peak by removing 3 turns on my T1 longest winding. Now, the peak is at scale x7 and quite all segments lighted.

It is difficult to tell you where the problem is, you should try to follow the troubleshooting procedure that Hans wrote. Low signal when looking for the BPF peak can be with a problem on the LPF (double check turns number, solder joints, etc.) also on T1 and, then, more difficult to find... on any place else after T1.

Hope you will find...

--
73 from Denis, F6GKQ
QCX 40m nr 3082


Liam Kingsmill <lumetters1@...>
 

Robert, thank you for the info.  The board here is labeled "3".  The power application problem seems to fit, however.

Liam


On 04/04/2018 08:42 AM, rentwist@... wrote:
Liam,

You need to do the start-up mod if your board rev is 1 or 2 (number on lower right of board).  http://qrp-labs.com/qcx/qcxmods.html#pwrup

BTW, there are a number (4 at least that I recall) recommended mods for any PCB prior to rev 3.

Hope this helps (think it will).

73,

Robert, WA2T


Daniel Urbach
 

I ha e followed the trouble shooting manual that Hand has provided however the BPF section is quite lacking. My problem is not that it does NOT peak...it is that my highest reading is a scale factor 4. That is with no load or resister applied. I have built mine for the 40 meter band. Also my peak occurs with the cap plates approximately half meshed .


Alan de G1FXB
 

Hi Daniel,

To as to provide a background to your problem,
what version QCX40  have you, 1/2 or 3?
What firmware revision?
Have you carried out any of the modifications if your unit is Ver 1 or 2 production?
At first power up, you entered the correct band info. And not had to tune far to get to 40Mtrs?
(better still start afresh and do a factory reset, so as to be sure. So it's a known starting point.)


As pointed out in Example 3
https://www.qrp-labs.com/qcx/qcxtrouble.html#examples
  one possible reason to obtaining a peak, but of low amplitude and COULD be a indication of problems that are located elsewhere rather than the BPF area.

All pins of MCU IC2 are correctly inserted & not bent under the IC etc?
Are your DC voltages correct, particularly around the OPamps? given in the build manual section 6.4

While reading the troubleshooting page,
(read the whole section, as resistors of different values are temporary shunted incircuit to aid diagnostic checks,
depending on the different signal levels expected.)

The QCX alignment requires the correct generation of the alignment signal.
https://www.qrp-labs.com/qcx/qcxtrouble.html#siggen
Is this the correct amplitude?
What is your signal amplitude at the first T1 Check?
https://www.qrp-labs.com/qcx/qcxtrouble.html#t1
as this may give an indication as to any excessive attenuation from Antenna jack to BPF stages.
Also related, What is your TX power?
(may indicate problem in LPF section)

(It's bad practice to jump around circuit blocks, but as a time saver)
Are your I/Q signal amplitudes close to what Hans gives in his troubleshooting example at say IC5 pin 1 & 7?
https://www.qrp-labs.com/qcx/qcxtrouble.html#ic5
(It's a nice verification that all is good in the RF quadrature & I/Q signals, as they should display a clean 90 degree shift with similar amplitude.
And should tell you to which side of the circuitry from that point you should look.)


If your results are good so far, then while in the BPF diagnostic mode the bar graph is reported by the QCX  by sampling the level found at the audio 2 test point.
Therefore close examination is required to the circuitry between IC5 Pin 1/7 and this location. Again the troubleshooting page gives guidance to what to expect.
(Subsequent alignment steps, samples the level at another location)

Please advise what you find.

Alan


On 04/04/2018 22:12, Daniel Urbach wrote:
I ha e followed the trouble shooting manual that Hand has provided however the BPF section is quite lacking. My problem is not that it does NOT peak...it is that my highest reading is a scale factor 4. That is with no load or resister applied. I have built mine for the 40 meter band. Also my peak occurs with the cap plates approximately half meshed .


Daniel Urbach
 

I have no test equipment available to me save for a dvm. I have no idea of the amplitude of any signals. I have adequate (quite loud) audio. It is a rev 3 (two weeks old) 40 m kit. I have carefully inspected solder joint and component installation in general.....I am not without signal in step 8.7 it is just quite low....it also peaks about as I would expect..... Supsequent steps all are "normal" ....yes it is set in the correct band.  Thank you for the reply......


Gadget Lust <gadgetlust@...>
 

Simple, but often effective and revealing, put the rig in BPF alignment mode, then, carefully and gently use a non-conductive plastic tool or a rubber eraser to lightly apply pressure on components and coils, listening for a change in tone or amplitude.   This may reveal a cold solder joint, shorted, or sheared component, and narrow the problem down.   Has worked for me on these kits and in many other troubleshooting situations.

Good luck and 73,
--
Harv
K2PI
Warrenton, VA


Liam Kingsmill <lumetters1@...>
 

Robert, WA2T

There's another variation with this version 3 QCX "power on" that I forgot to mention.  What's different from PCB version 1 and 2: always, when #3171 power is applied the LCD also immediately lights up with the normal information.

I've read the LCD of the two versions prior to version 3 did not show the initialiazation info.

Liam


Daniel Urbach
 

I have to admit that I am a little disappointed that fully half of the replies to this thread are answers to an unrelated problem that some else inserted here.