Hi Alan,

Thanks for your advice.

• I have used a different 13.8V fixed voltage power supply instead of my benchtop variable voltage lab supply => no change
• I did the factory reset => no change

You are right, missing signal from the internal test routine could result in the symptoms I am seeing. I probably could adjust the filter with the noise signal, but I fail on subsequent receiver adjustments for lack of a detectable signal. I will try to feed a signal from an external signal generator into the antenna jack and see if I can then adjust the receiver.

73 Heinz?

Graham (and Hans),

Based on Hans' emails regarding locking an Si5351A synth module to a 10 MHz external reference (Rubidium, in my case), I can confirm that I was successful, based on the Nov. 2017 ARRL Frequency Measuring Test results. I invested in a VFO/SigGen kit with relay-switched LPF kit and got it operational about 1 minute before the FMT started.? I set the reference frequency to 10 MHz (vs. 27 MHz) and was ready to go with a frequency difference measuring technique and Spectrum Lab software.? My first measurement was a bit over 1 Hz error; the remaining 3 measurements were less than 1 Hz error.? With a bit of practice, I hope to get all measurements < 0.1 Hz error.

My Rb standard power output is a little low- about 3-4 dBm into 50 Ohms.? The 10 MHz reference signal goes directly into the Si5351A pin 2 (crystal pad) and ground on the synth. module board.? I plan on adding a 10 MHz CMOS crystal oscillator to the VFO/SigGen kit soon with an external BNC-BNC jumper cable so the siggen doesn't require the Rb standard for basic operation.? The Rb oscillator is an LPRO-101.? The LPRO AC-coupled output RF is split using a Minicircuits LRPS-2-1 in-phase power splitter.? The LPRS DC resistance of an output measures close to zero Ohms.? Then the output is wired directly to the BNC output connector.? So not external DC biases are applied; similar to what a crystal would do.

Hi,

I have finished assembly of my 40m version of the QCX.

The transmitter works fine, has a clean and stable output as checked with another receiver. I get 2.8W HF out at 12.0 VDC / 0.46 A in or 4.0W out at 14.0 V / 0.52 A in. I do not hear any sidetone in the receiver during keying the TX.

The first step of receiver alignment, adjusting the band-pass trimmer was OK. I got a peak after removing 5 turns of? T1. When I proceeded to the adjustment of the I-Q balance trouble started. With the volume control full left (fully counterclockwise) I have no significant signal level on the amplitude bar (as it should). When I adjust the volume control clockwise the amplitude bar shows some signal, but it jumps up and down. The division ratio jumps from 3 to 7 without me touching anything. With the amplitude bar jumping there is no way I could adjust I-Q balance. It is the same with 90-degrees phase shift adjustment, amplitude bar and division ratio jump up and down like crazy.

I can hear no sidetone in the earphones during these adjustment steps, although there is a warning to take out the earphones because of the loud tone. There is no sidetone during transmit either.

I have the correct values for the multi-turn trimmer resistors R17, R24 and R27. I have resoldered all joints. The voltages at all ICs are roughly as they should per table on page 125. I have checked continuity of all T1 windings.

I have tried both, no connection at the antenna port or connection to a 50 Ohm dummy during adjustment. This makes no difference.

Any ideas what I could check next?

73 Heinz, OE5EEP

Alan. Thank you for your mail. I have hesitated answering until I had some more info. I reset the unit to the factory setting. Now I am able to receive very powerful stations and I believe a station heard me. But the audio is so overwhelming and must turn audio pot almost all the way up. The next thing to do is check RF output. Then maybe restart the alignment again. If you have anymore thoughts please send them. They sure make a guy think! Big thanks again for trying to help. I have taken 4 turns from T1 and may take another off. I am 90 so this is exciting when something helps. Thanks Hans.? Glen n8we

?

From: Alan de G1FXB via Groups.Io

Sent: Thursday, January 18, 2018 2:46 PM

To: [email protected]

Subject: Re: [QRPLabs] QCX- No xmit or receive.

?

Hi Glen,

On 18/01/2018 17:19, Glen Sr wrote:

Could Q5 be open?

Any thing is possible.
Taking a clue from your subject field. It will not prevent Transmit function though.
There are no Transmit / Receive relays or PIN Diode switching in this design.
Look at the schematic and Han's write up of how that stage works in section 5.8
the transmit PA devices are permanently connected to the LPF and Antenna jack.
Q5 provides couples the RX circuitry to the antenna jack during RX & providing isolation to prevent damage to the switcher / detector IC during TX cycle.

If Q5 was open I would expect the unit should still transmit.

Can I jumper Q5 to see if I can hear a signal without further damage? Glen N8WE

If you suspect Q5 pull it from the board.
it's a N-channel FET, there is a bit of an knack to measuring FET's because they are a high input impedance device.
Iif you read the junctions in any old order you can land on the combination that turns the gate on, then you move the test leads to source & drain. And you then convince yourself it's faulty when it's not....

Ideally if you have one of those cheep Chinese component testers use that, if you use a meter then perhaps Google is your best friend for tips before you try yours.



If Q5 is not faulty, logical fault finding is the best approach.

Re-read the assembly manual, even the sections printed in red.

QCX home page, has a common issues section.

QCX Mods page, has MOD's and component changes you need to be aware of, depending on your kit S No#

Has the unit ever worked correctly then failed, or is it a new build that's never worked?

Unit aligned correctly, through each section, strange behaviour or anything that you were not sure about?
(motorboating, moving bar graphs when you were not adjusting anything, warm smells / magic smoke?)

Compared your voltages to typical ones given in the troubleshooting section of the manual?



let us know what you find.
If there is nothing conclusive, a good photo image of the component side & solder side of the PCB with the LCD removed and we can look at anything with a fresh pair of eye's.
What test equipment have you access to?


Regards Alan

Hi Dave,
Glad the desperate 'factory reset' worked!

Alignment is a bit chicken & egg, As they all interact.
Hans didn't give any starting positions as to where the multi-turn presets should start from. Straight from the component supplier you would guess it's random.
I think I would start from mid point, it's not PA bias or anything that will cause excess current draw if incorrect?

It's a shame there is a limitation in the lowest freq the synth can output and there is no convenient way to divide by five or six in the QCX....
otherwise IF IT could generate two (90° ?) phase shifted 700Hz audio channels on CLK0 & CLK1 and with a bit of linking we could
pre-align the audio I/Q filter strip and prove everything is OK in 95% of the circuit before tackling the black magic of the RX RF stage & BPF / C1 peaking....

?
Don't suppose you have an audio generator capable of 700Hz
Or you are the type to breadboard stuff up temporary?

regards Alan

On 20/01/2018 22:22, dave dabay wrote:

factory reset pins a 14.020 now, but I am not sure it is hearing much...as the others have said,

I have been able to tweak the pots and that seems to work under the "adjust IQ balance on page 65

one step at a time.?? Next step is to verify that the received "hears"

thanks

factory reset pins a 14.020 now, but I am not sure it is hearing much...as the others have said,

I have been able to tweak the pots and that seems to work under the "adjust IQ balance on page 65

one step at a time.?? Next step is to verify that the received "hears"

thanks