Topics

QCX 20m no power #qcx #problem

John
 

Just recently acquired a SWR capable of HF frequencies. So today I connected my QCX to my QRP-guys no tune ended with about 28ft of wire connected to it.
Had no trouble whatsoever with the alignment besides at the very first start a short on the volume pot. After that was fixed I was able to allign the QCX20.
But now with the SWR connected I had no passthrough power, no passthrough peak power and no SWR indication. I exchanged my QCX with a Pixie and that one is putting out power although I had a bad SWR.
So guess have to pull out the scope once again, although it is only 10MHz bandwidth, to see what is going on. 

Anyone hints where to start looking? Where are the most mistakes made?

Thanks, 

John

Allen Poland
 

The antenna you connected to it.  What does that mean?  How bad was the SWR?

 

Check continuity from the finals to the antenna center connector.

 

Could be two things.  High SWR wiped the finals…..or you have an open/short from the finals to the output jack.

 

When you connected the antenna did you hear anything?

 

K8AXW

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of John
Sent: Thursday, August 30, 2018 6:20 PM
To: QRPLabs@groups.io
Subject: [QRPLabs] QCX 20m no power #problem #qcx

 

Just recently acquired a SWR capable of HF frequencies. So today I connected my QCX to my QRP-guys no tune ended with about 28ft of wire connected to it.
Had no trouble whatsoever with the alignment besides at the very first start a short on the volume pot. After that was fixed I was able to allign the QCX20.
But now with the SWR connected I had no passthrough power, no passthrough peak power and no SWR indication. I exchanged my QCX with a Pixie and that one is putting out power although I had a bad SWR.
So guess have to pull out the scope once again, although it is only 10MHz bandwidth, to see what is going on. 

Anyone hints where to start looking? Where are the most mistakes made?

Thanks, 

John


Virus-free. www.avast.com

John
 

The SWR on the Pixie said 1:5. So would need to shorten most likely, cut it a little longer than instruction said. Antenna is a qrp-guys no tune ended.
Had the wire in the house so that could also be a reason for the high SWR.
I did hear a faint signal on 14.074 (FT8). So it does receive, audio level is also pretty low so also have to look into that.
Haven't really used it so far other than with a dummy load attached so don't think I already blew my finals.
Was my first build after a short while of absence from electronics. Before that I only repaired the audio section of my uBitX (famous TDA2822 smoke).

Somewhere next week will get the scope out and see what's going on.

John

@CurtisM
 

John

Time to slow down a bit. I am wondering if you have a non connection in one or more LPF inductors, as this would cause weak reception and not much transmit. Check these connections with dc turned off, with a dvm for continuity. Check pad to pad without touching wires. Do examine schematic while checking with dvm. I recommend getting receive working with, with fully successful alignment before any more transmit tests. Also use your dummy load instead of an unknown antenna.

73 curt

Allen Poland
 

John,

 

1.5 SWR on the Pixie is great.  However, the output impedance of your QCX might be something else which would give you a high SWR reading.

 

I’m not familiar with your antenna so can offer no advice there.  I’d tune it into a dummy load and see what power I was getting out.  If it was satisfactory, then I would concentrate on matching the antenna to the QCX according to your antenna instructions or with a tuner.  Care must be taken with the tuner though.  Others are no doubt more knowledgeable about this than me.  Is the antenna a “balanced” antenna like a dipole?

 

K8AXW

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of John
Sent: Friday, August 31, 2018 5:50 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QCX 20m no power #problem #qcx

 

The SWR on the Pixie said 1:5. So would need to shorten most likely, cut it a little longer than instruction said. Antenna is a qrp-guys no tune ended.
Had the wire in the house so that could also be a reason for the high SWR.
I did hear a faint signal on 14.074 (FT8). So it does receive, audio level is also pretty low so also have to look into that.
Haven't really used it so far other than with a dummy load attached so don't think I already blew my finals.
Was my first build after a short while of absence from electronics. Before that I only repaired the audio section of my uBitX (famous TDA2822 smoke).

Somewhere next week will get the scope out and see what's going on.

John




Avast logo

This email has been checked for viruses by Avast antivirus software.
www.avast.com


John
 

This is the antenna I'm talking about:
https://qrpguys.com/qrpguys-end-fed-wire-antenna

Not sure if my SWR is working properly. Or if the cabling is 100%. Will check that too with an analyzer. 
But in one thing I'm sure the pixie send power through the SWR which the QCX did not.

Will also check the connections of the toroids.

John

Chopper
 

At this point in your debug you will be better off with a small 50 Ohm dummy load. At 5 watts very easy to make if you don't have one.   Just use non inductive resistors

John
 

Have a 50W dummy load so that is not a problem.
Just have to find the time to investigate.

John

John
 

But as the qrp-guys antenna is also a kit better check that one too ;)
Have an antenna analyzer so that would be easy to do.

John

Allen Poland
 

Checked out the antenna…here’s the first thing that hit me:  The SWR is further broadened and lowered across 80m-10m with a high voltage capacitor on the primary of the transformer using band specific radiator lengths. It is designed to use without a tuner and give an SWR of ≤1.2 for any portion of the band after optimizing the driven element. (Emphasis mine)

 

All fixed tuned output transmitters are not necessarily 50 ohms or will work properly (without retuning the antenna) from one rig to another.  Notice that others on this forum are having problems with the finals blowing while they try to tune up their antennas with an automatic tuner (read fast tuning here)!

 

I don’t have an answer except for you to confirm you rig is putting out the expected power into a dummy load and tune your antenna with an analyzer. 

 

Don’t use any other rig to tune your antenna and then put the QCX on expecting the match to be correct.

 

I also concur with others that you should re-inspect your QCX  bandpass filter in conjunction with the tuning cap plate position….and circuit continuity.  Especially the  toroid connections.

 

K8AXW

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of John
Sent: Saturday, September 1, 2018 7:41 AM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QCX 20m no power #problem #qcx

 

This is the antenna I'm talking about:
https://qrpguys.com/qrpguys-end-fed-wire-antenna

Not sure if my SWR is working properly. Or if the cabling is 100%. Will check that too with an analyzer. 
But in one thing I'm sure the pixie send power through the SWR which the QCX did not.

Will also check the connections of the toroids.

John




Avast logo

This email has been checked for viruses by Avast antivirus software.
www.avast.com