calculating L1 - L3 inductance #20m #40m #toroid


Syd
 

I'm thinking about rewiring these inductors using 28 GA magnetic wire instead of what was supplied with the kit by Hans. What size wire is Hans using for his coils? In other words, I'm looking to figure out how many turns I will have to wind to get the same inductance as originally specified in the construction of these coils from the construction manual. From looking at the online inductance calculator, the wire size will make a difference in the inductance of the coil; ie, going from 2mm to 3mm wire will make an appreciable difference in inductance, (about 2.95uH vs 2.13uH) so how much will using 28 GA wire make a difference in the number of turns I need to wind. Should I even be concerned about this error because of wire size and just start making the coils with what I have.
syd/wt1v


 

Nope, don't worry about it: reasonable & practical variation in wire diameter won't make a significant difference to inductance. Winding tightness and variation in the core, turns spacing, tolerance of companion capacitors together with other factors will make more of a difference, collectively.
--
Julian, N4JO.


Fred Spinner
 

Drop a turn off of them.  If you have a NanoVNA it's pretty easy to measure the inductance even on those low uH inductors. Just match them.  Spreading and bunching the turns might be able to do it too.  I like my toroids a bit stiffer on the board, but another alternative is to use some craft hot glue and just glue them down too. Easily removable later.  Or even Epoxy which isn't.

Fred W0FMS 

On Sun, Oct 31, 2021, 11:16 AM Syd via groups.io <nhuq1=yahoo.com@groups.io> wrote:
I'm thinking about rewiring these inductors using 28 GA magnetic wire instead of what was supplied with the kit by Hans. What size wire is Hans using for his coils? In other words, I'm looking to figure out how many turns I will have to wind to get the same inductance as originally specified in the construction of these coils from the construction manual. From looking at the online inductance calculator, the wire size will make a difference in the inductance of the coil; ie, going from 2mm to 3mm wire will make an appreciable difference in inductance, (about 2.95uH vs 2.13uH) so how much will using 28 GA wire make a difference in the number of turns I need to wind. Should I even be concerned about this error because of wire size and just start making the coils with what I have.
syd/wt1v


Hans Summers
 

And anyway... The wire in the kits IS #28. Or at least, very close to it. 

73 Hans G0UPL
http://qrp-labs.com


-------- Original message --------
From: Julian N4JO <n4jo@...>
Date: Sun, Oct 31, 2021, 9:22 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] calculating L1 - L3 inductance #20m #40m #toroid
Nope, don't worry about it: reasonable & practical variation in wire diameter won't make a significant difference to inductance. Winding tightness and variation in the core, turns spacing, tolerance of companion capacitors together with other factors will make more of a difference, collectively.
--
Julian, N4JO.


Syd
 

Interesting thoughts. I did take out L1 - L4 and could now very that the filter caps were correct. Then I took out my LCR meter and measured the inductance of each coil and I could see that they needed adjusting.  I fixed all of them to match the inductance values given in the 40m table. Most of them took a few turns off to adjust the inductance. I did measure the cap values with the meter and they were right on so I guess the LCR meter is pretty accurate and probably so should the inductance measurements.  I did look at the PA output waveform at 12v supply and found a 30v pp waveform so it looks like the PA is OK and I'm back to the LPF section.  Interesting that I just received my NanoVNA just a few days ago, so I'll be using it to check the inductance values that way also.
73 wt1v