#18447

Hi folks,

I received my QCX 80 Mtr kit a couple weeks ago (kit no. 1536) and its now finished and undergoing tests. The only part of the kit I had some difficulty with was the transformer (T1 on the schematic) which becomes a little crampt on the 80 Mtr version due to the number of turns required.

Being a member of the "older" generation my eyesight is less-than-perfect and I rely on a magnifier which helps but also causes a reduced depth of field so all the connections on T1 are hard to see clearly. Anyway, after winding the transformer I decided it looked a bit rough so I re-wound it a second time before finally fitting it to the PCB but the second time around I found a method which made identification of the individual windings much easier.

If you have some spare coil wire/magnet wire kicking around in the junk box which is a different colour to that supplied with the kit then wind each winding with a different colour, it makes identification of the connections much easier and final assembly into the PCB becomes a breeze.
BTW, my T1 still looks terrible but works a treat :-)

73,s

Des (M0AYF)

[email protected]

#19172

Hi Des (again) and others
I just searched this topic and your name came up again.
I had to have 3 attempts to wind the T1 transformer.

On the first attempt, I ran out of 28swg wire to complete the winding having obviously?used generous amounts for the other inductances.
(QRP Labs - please note that a little more wire would not go amiss).
I had some 27swg and 30swg wire and decided to try the 27swg?but trying to wind 83 turns on a T50-2 toroid is no easy task and I abandoned this in favour of the 30swg.

I managed to wind the transformer with quite a bit of overlap of 30swg wire and I presume I have wired it up correctly as I am now hearing stations? reasonably well from continental Europe. Obviously, 30swg wire?is quite delicate but it?is certainly workable if one is careful.

The issue I have is with the alignment: it is starting to peak but I am only achieving a scaling factor of 5 with the plates of C1 completely closed and I now have to add some more turns.
For optimum performance,?is the target value around 9 as indicated in the manual and I am wondering whether it is easier to remove turns rather than add.
In other words, would it be better to add 10 turns rather than 5 turns as suggested in the manual ?

Again input from you or any other would be most welcome.

73s

Robin
G4DNP

#19177

开云体育

Robin,

At this stage, rather than add turns, why not add some extra capacitance across the trimmer? I would imagine the L/C ratio isn't critical in this instance. As a start, I'd try something a little less than the range of the trimmer itself. I don't have the information to hand but if the trimmer is say 5 to 40pF then something around 30pF can't be too much.

Just tack the cappy on the back of the board at this stage.

Of course you might need more capacitance still, but it's an easy experiment to make.?

Regards,?

John

G4YTJ

Sent from my mobile phone

Show quoted text

-------- Original message --------
From: robin.travis@...
Date:
To: [email protected]
Subject: [QRPLabs] Winding Tip for 80 Mtr QCX transformer (T1)

Hi Des (again) and others
I just searched this topic and your name came up again.
I had to have 3 attempts to wind the T1 transformer.

On the first attempt, I ran out of 28swg wire to complete the winding having obviously?used generous amounts for the other inductances.
(QRP Labs - please note that a little more wire would not go amiss).
I had some 27swg and 30swg wire and decided to try the 27swg?but trying to wind 83 turns on a T50-2 toroid is no easy task and I abandoned this in favour of the 30swg.

I managed to wind the transformer with quite a bit of overlap of 30swg wire and I presume I have wired it up correctly as I am now hearing stations? reasonably well from continental Europe. Obviously, 30swg wire?is quite delicate but it?is certainly workable if one is careful.

The issue I have is with the alignment: it is starting to peak but I am only achieving a scaling factor of 5 with the plates of C1 completely closed and I now have to add some more turns.
For optimum performance,?is the target value around 9 as indicated in the manual and I am wondering whether it is easier to remove turns rather than add.
In other words, would it be better to add 10 turns rather than 5 turns as suggested in the manual ?

Again input from you or any other would be most welcome.

73s

Robin
G4DNP

#19178

Good comment John. I'm suprised it has'nt been made before - or has it.

Show quoted text

On 6 Dec 2017 at 17:36, John Pagett wrote:

Robin,
At this stage, rather than add turns, why not add some extra capacitance
across the trimmer? I would imagine the L/C ratio isn't critical in this
instance. As a start, I'd try something a little less than the range of the
trimmer itself. I don't have the information to hand but if the trimmer is
say 5 to 40pF then something around 30pF can't be too much.
Just tack the cappy on the back of the board at this stage.
Of course you might need more capacitance still, but it's an easy experiment
to make.?
Regards,?
John
G4YTJ


Sent from my mobile phone

-------- Original message --------
From: robin.travis@...
Date:
To: [email protected]
Subject: [QRPLabs] Winding Tip for 80 Mtr QCX transformer (T1)

Hi Des (again) and others
I just searched this topic and your name came up again.
I had to have 3 attempts to wind the T1 transformer.

On the first attempt, I ran out of 28swg wire to complete the winding having
obviously?used generous amounts for the other inductances.
(QRP Labs - please note that a little more wire would not go amiss).
I had some 27swg and 30swg wire and decided to try the 27swg?but trying to
wind 83 turns on a T50-2 toroid is no easy task and I abandoned this in
favour of the 30swg.

I managed to wind the transformer with quite a bit of overlap of 30swg wire
and I presume I have wired it up correctly as I am now hearing stations?
reasonably well from continental Europe. Obviously, 30swg wire?is quite
delicate but it?is certainly workable if one is careful.

The issue I have is with the alignment: it is starting to peak but I am only
achieving a scaling factor of 5 with the plates of C1 completely closed and I
now have to add some more turns.
For optimum performance,?is the target value around 9 as indicated in the
manual and I am wondering whether it is easier to remove turns rather than
add.
In other words, would it be better to add 10 turns rather than 5 turns as
suggested in the manual ?

Again input from you or any other would be most welcome.

73s

Robin
G4DNP

[email protected]

#19184

Good idea John, I have a few trimmers in the junk box that will do the job and it might give an idea how much extra inductance is required so I can calculate the number of turns required Thanks Robin G4DNP

#19216

Hi Robin & the group,

I see a number of people have allready responded with some good advice on this one but heres my 10p (10c) worth.

I would go along with the idea that adding a small capacitor in parallel with the trimmer is the simplest option and saves the "stress" of changing the number of turns on T1 and the only issue I can see with that is that by adding a capacior accross the trimmer you slightly reduce the total "swing" or range of tuning possible for T1. So at some future date you may want to peak in a different part of the band and not be able to do so due to the reduced tunning range. In practical terms it may not matter very much as the receiver is very sensitive and even signals off-tune are still of easily copied. My QCX is "peaked" at 3.560 MHz but still works perfectly well over the rest of the CW range. I "peaked" around 3.560 MHz to make it most sensitive in the area where one might expect to hear other (possibly weak) QRP signals.

Regarding "tweaking" T1 turns. I wound my T1 with too many turns on purpose with the notion that it would be easier to take turns off as oposed to adding them. I soldered all but one terminal of secondary 3 into the board permanently. The end of the secondary 3 winding (tuned winding) was soldered in "lightly" so it could be removed without to much difficulty. I had to remove quite a few turns on my T1 but with the aid of a pair of tweezers a few turns at a time can be removed with patience and the end of the tuned winding re-soldered. I seem to remember it took me 3 or 4 re-workings before I got my trimmer roughly mid-position.

73,s

Des (M0AYF)

#19262

Hi Tom,

Good tip :-)

73,s

Des (M0AYF)