Toroid material for QRP HF tuner: "2" or "6"?


moshecontra
 

I'm contemplating building a Z-match tuner.  They can be made rather compact if low-voltage capacitors are used (OK for QRP) and the coil is wound on a toroidal core (rather than air-wound).  EMtech sell a nice kit of such a tuner, but I prefer to design and build my own.  There are many designs on the web.  Getting the variable capacitors seems like the hardest (and most expensive) aspect, especially if you want to make the tuner capable of somewhat higher power than strict QRP, say 50 watts.


One thing that I'm puzzled about is the choice of core material for the coil.  It appears that material "2" (as in a "T130-2" toroid, for example) is good for lower frequencies, at least down to 3.5 MHz, but not so good for the high end of the HF range, while material "6" is good for higher frequencies, up to 30 MHz and more, but not so good for 80m.  If you want to build a tuner for the 3.5-30 MHz range, which core is the best compromise?  This may depend on your personal preferences regarding bands used?


Judging by the plurality of designs, "2" is more commonly used, but perhaps the designers were more interested in 80m than 10m?  See for example one early article about a Z-match with toroidal core, by Lloyd Butler - he used a "2", but measured the efficiency, and found it marginal on 10m.



Don Wilhelm <w3fpr@...>
 

The type 6 cores (Yellow) can work OK for 80 meters, but need more turns than type 2.

73,
Don W3FPR

On 6/5/2015 3:09 PM, mbraner@... [4sqrp] wrote:
 

I'm contemplating building a Z-match tuner.  They can be made rather compact if low-voltage capacitors are used (OK for QRP) and the coil is wound on a toroidal core (rather than air-wound).  EMtech sell a nice kit of such a tuner, but I prefer to design and build my own.  There are many designs on the web.  Getting the variable capacitors seems like the hardest (and most expensive) aspect, especially if you want to make the tuner capable of somewhat higher power than strict QRP, say 50 watts.


One thing that I'm puzzled about is the choice of core material for the coil.  It appears that material "2" (as in a "T130-2" toroid, for example) is good for lower frequencies, at least down to 3.5 MHz, but not so good for the high end of the HF range, while material "6" is good for higher frequencies, up to 30 MHz and more, but not so good for 80m.  If you want to build a tuner for the 3.5-30 MHz range, which core is the best compromise?  This may depend on your personal preferences regarding bands used?


Judging by the plurality of designs, "2" is more commonly used, but perhaps the designers were more interested in 80m than 10m?  See for example one early article about a Z-match with toroidal core, by Lloyd Butler - he used a "2", but measured the efficiency, and found it marginal on 10m.




Chuck Carpenter
 

Moshe,

I tend to build z-matchers to cover low HF and hi HF. One covers 160 thru 20 meters with type 2 cores. Others covers 40 meters thru 10 meters using type 6 cores.

Also build a few single band versions such as 10 and 6 meters using type 10 cores (black).

I like the designs from Charlie Lofgren, W6JJZ, and find them to have a wide impedance matching range and good measured efficiency.

You can find his designs in ARRL Antenna Compendium #5 and here: http://www.seboldt.net/k0jd/z-match.html

For measurements the AI1H procedure found in QEX for Sep/Oct 2003

and PDF here:

<http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CDMQFjAG&url=http%3A%2F%2Fwww.nonstopsystems.com%2Fradio%2Fpdf-ant%2Fradio-tuners-baluns.pdf&ei=6v5xVdKqEpawogSct4GABw&usg=AFQjCNF9O06mZxwtcJ3ln-46OgrR_i89PQ>


Chuck Carpenter, W5USJ
EM22cv, Rains Co. TX


moshecontra
 

Thanks for the pointers.  That Lofgren writeup includes these comments:

"I recommend a T-130-6 core, which gives better Q throughout the HF range than is attainable with a T-130-2 core. But either one is satisfactory. The important point is that the cores differ in permeability, so the number of turns will differ depending on which one is selected."

He also explains how to alter the inductance of the coil to fit the range of capacitance you happen to have on hand. And his way of tapping the coil (with ground in the middle instead of an end) supposedly offers somewhat better balance - for balanced loads.


Shawn Reed
 


Also...Considering it would be easier to pick up the difference with a resonant ant. at the higher end...I would favor the lower end of rf freq., with some good variables working. There also is the coin to toss. 73,Shawn

On Friday, June 5, 2015 12:09 PM, "mbraner@... [4sqrp]" <4sqrp@...> wrote:


 
I'm contemplating building a Z-match tuner.  They can be made rather compact if low-voltage capacitors are used (OK for QRP) and the coil is wound on a toroidal core (rather than air-wound).  EMtech sell a nice kit of such a tuner, but I prefer to design and build my own.  There are many designs on the web.  Getting the variable capacitors seems like the hardest (and most expensive) aspect, especially if you want to make the tuner capable of somewhat higher power than strict QRP, say 50 watts.

One thing that I'm puzzled about is the choice of core material for the coil.  It appears that material "2" (as in a "T130-2" toroid, for example) is good for lower frequencies, at least down to 3.5 MHz, but not so good for the high end of the HF range, while material "6" is good for higher frequencies, up to 30 MHz and more, but not so good for 80m.  If you want to build a tuner for the 3.5-30 MHz range, which core is the best compromise?  This may depend on your personal preferences regarding bands used?

Judging by the plurality of designs, "2" is more commonly used, but perhaps the designers were more interested in 80m than 10m?  See for example one early article about a Z-match with toroidal core, by Lloyd Butler - he used a "2", but measured the efficiency, and found it marginal on 10m.