Topics

Failure to get a sufficiently high BPF Peak #qcx #bpf #alignment #40m

william.wallace1@...
 

Hello and greetings, 
My name is Will Wallace and my class mate Joe Corbin and I are building the QRP Labs QCX 5W CW Transceiver as a part of a class. We are both students studying engineering at Ottawa University, up to this point the project has been going extremely well, but once all of the hardware was installed, and we ran power through the device into a dummy load and began the alignment process, we could not get a BPF Peak of over four. Does anyone have any insight as to how we can go about fixing this? I am sure its an improperly installed hardware component, but with the both of us being so new to this neither of us are entirely sure which components need to be tested. 
Thank you, 
William Wallace

Jim Mcilroy
 

Hi

If you have access to an LCR meter I suggest you measure the toroid windings.

I’ve built one (QCX40) and I had to take off a couple of turns. From my notes I reckoned it was around 0.1uH/turn.

It also depends on how ‘elegant’ the windings are. I.e. loose v tight. That will change readings a bit. 

Try this. You won’t break anything.

73

Jim


On 18 Nov 2019, at 02:27, william.wallace1@... wrote:

Hello and greetings, 
My name is Will Wallace and my class mate Joe Corbin and I are building the QRP Labs QCX 5W CW Transceiver as a part of a class. We are both students studying engineering at Ottawa University, up to this point the project has been going extremely well, but once all of the hardware was installed, and we ran power through the device into a dummy load and began the alignment process, we could not get a BPF Peak of over four. Does anyone have any insight as to how we can go about fixing this? I am sure its an improperly installed hardware component, but with the both of us being so new to this neither of us are entirely sure which components need to be tested. 
Thank you, 
William Wallace

william.wallace1@...
 

Thank you sir! We will try this out first thing in the morning. I do believe that we have access to LCR meter. 

Ronald Taylor
 

One thing you might want to consider doing first is to check continuity through the lowpass filter. This can be done by checking from the center pin of the BNC connector to junction of L3 and C27. If any of your solder connections to the enamel wire on the L1-L3 torroids is bad, it will inhibit the test signal from getting through to the receiver input. 

Best 73… Ron

On Sun, Nov 17, 2019 at 8:33 PM <william.wallace1@...> wrote:
Hello and greetings, 
My name is Will Wallace and my class mate Joe Corbin and I are building the QRP Labs QCX 5W CW Transceiver as a part of a class. We are both students studying engineering at Ottawa University, up to this point the project has been going extremely well, but once all of the hardware was installed, and we ran power through the device into a dummy load and began the alignment process, we could not get a BPF Peak of over four. Does anyone have any insight as to how we can go about fixing this? I am sure its an improperly installed hardware component, but with the both of us being so new to this neither of us are entirely sure which components need to be tested. 
Thank you, 
William Wallace

Chopper
 

Where is the volume control set?
Check the connectivity of all the T1 windings using the solder pad as the test point ( not the end of the wire).  Many times issues with the peaking ins due to poor solder connections due to the enamel on the wire.

ajparent1/KB1GMX
 

I will rephrase the earlier as it maybe unclear to a new user.

The level display on the LCD is relative to the volume control.
Set if for some level in the middle of range then try to peak it.

Allison
--
Please reply on list so we can share.
Off list email goes to trash, I had to due to scrapers.

Hans Summers
 

Hi William, all: 

A minor point: BPF peaking 8.7 does not depend on the volume control setting. This is because it is sampled from Audio2, which is BEFORE the volume control in the signal path through the receiver. The other alignment menu tools "8.8 I-Q bal", "8.9 Phase Lo" and "8.10 Phase Hi" are sampled from Audio1 which does come AFTER the volume control and therefore the volume control setting does affect the reading on screen. This is because the further gain was needed for unwanted sideband measurement, since the signals are up to 60dB or more weaker after good cancellation. 

The fact that you have any BPF reading at all seems to indicate that at least something is working as it should be. The low reading could be due to:
  • Non resonant BPF tank circuit in T1... possibly due to incorrect number of turns. We do not usually find it necessary to adjust the number of turns on the long winding, however. You did not mention which band you built - for 40/30/20/17 band versions I think the trimmer capacitor range is normally enough and you should not need to mess with the number of turns. 
  • Mis-soldered wires around T1... either wires in the wrong holes, or wires not soldered properly because the enamel wasn't burned off. Does turning the trimmer C1 have any effect? If not, then this could indicate the wires of the long winding are not soldered properly, and therefore there is no electrical connection. Be particularly careful with soldering wires which are grounded, because the ground plane tends to suck away the heat and make a good clean joint less easy to achieve. 
  • When you have the volume set to around mid-range and you turn the rotary encoder from "8.7 Peak BPF" to "8.8 I-Q Bal" the tone will usually get significantly quieter (in 8.8). If it does not, you might have a fault in one of the signal paths I and Q, around IC5/6/7 that is preventing cancellation. That would also prevent addition of the in-phase signals of the wanted sideband, therefore lowering volume. 
73 Hans G0UPL





On Tue, Nov 19, 2019 at 1:01 AM ajparent1/KB1GMX <kb1gmx@...> wrote:
I will rephrase the earlier as it maybe unclear to a new user.

The level display on the LCD is relative to the volume control.
Set if for some level in the middle of range then try to peak it.

Allison
--
Please reply on list so we can share.
Off list email goes to trash, I had to due to scrapers.

william.wallace1@...
 

Mr. Summers, 

Thank you for the response. We are building the 40 band version. The C1 tuning trimmer does have an effect on the BPF reading so we are getting some form of electrical connectivity through T1. Also, when performing the transition from "8.7 Peak BPF" to "8.8 I-Q Bal" we get a significant drop in the volume. This is leading me to believe that we have either a missed number of turns in T1 or, our turns are sloppy. We do have some instances of overlapping loops and kinked wire. I believe we will reattempt to wrap T1. 

William