Fw: Re: Fw: [Antennas] Tuner Inductor Q

Sun, 5 Jan 2003 17:54:08 -0600

Hi Wes, figured you would be in here. 
>A saying leaps to mind: If it sounds too good to be true then it
probably is.
>How are you determining these Q values? IMHO they are much too high.

I'm using a Boonton 260A which has been calibrated to be "pretty close"
using the Boonton working coil standards. Note that these are all
unloaded
Q measurements as you would expect, very short leads (3"), etc.
>I can't find my exact data, but I did measure (using a calibrated HP Q
>meter) an E. F. Johnson roller inductor that was similar in size to the
>ARC-5 roller and had the benefit of variable winding pitch. I don't
recall
>exactly the upper Q value but know that it was around 100~150. What
sticks
>in my mind however, is that at the lower inductance settings, the Q was
>down to 50 or so. These numbers are similar to what Karl reported
earlier
>on Palstar.

Those measurements I gave are for the coil on the ceramic form ONLY, no
roller is involved. The coil comes out of one of the ARC/5 Tx units where
it's normally used with a beveled roller which runs between turns (no
variable pitch). I just measured the coil, not using the roller assy. The
purpose of the quick test was to see if the Q would drop if the unused 
section was shorted ....it basically does not. I don't have a good roller
coil to test and compare to.
>Yes, that is why some rollers use variable winding pitch.

You bet.
>The author of the Eagleware modeling program (I know that's a nasty word
>with some here) has developed a new model for inductors that refutes the
>idea of turn-to-turn capacitance. For an intutive example consider a
coil
>that has a lot of close-wound turns. Must have a lot of turn-to-turn
>capacitance, right?

>Wrong. The phase shift from one turn to the next will be small (there
are
>a lot of turns and the phase shift from end-to-end is fixed). 
Therefore,
>the voltage and phase difference between turns is also small, which in
>effect shorts out the "capacitance" between turns. (See: "Filters and
an
>Oscillator Using a New Solenoid Model", Randy Rhea, Applied Microwave &
>Wireless, Nov. 2000, pp 30-42)

Well, what I'm talking about here are coils that are single level and
really 
don't have that many turns (like loading coils, receiver RF and osc coils
....like on the HBR HF receiver). I've seen time and time again that if
you 
space the turns, even by one wire diameter, the Q goes up. It does
require 
some additional turns to maintain the same inductance and, of course the 
coil will be physically longer. Multi level solenoid coils whether layer
wound, basket weave wound, or random wound are a different animal.
I don't know what Eagleware modeling assumed for their test device.
I did find that basket weave winding multiturn, multilayer coils like IF 
transformers does raise the Q a little (less capacitive turn to turn 
coupling). 
>Hold on a minute. A "broad" network can be obtained with high Q 
>components.

Sure, that's why I said "maybe" you would like the highest Q you can get
but you need to see what the result is ....how easy is the tuner to use. 
Also on the subject of "ease of use" tuning; with the high value tuning 
capacitor needed for 160m, optimum settings for other bands may be 
very sensitive in a 180 degree rotation of the knob. You can fix this by 
switching in additional gangs of capacitance (High Q while maintaining 
ease of use as you go from 10m to 160m). 
Any on a completely different tuner subject, the "Balanced, Balanced 
Antenna Tuner" by AG6K is gaining in popularity at the local club, I 
may build one. Looks like a great tuner but I would add a switchable 
choke balun on the frontend ....30-33ft of coax for 160m through 40m 
and around 12 ft of coax for 20m through 10m. Using the 30-33ft length 
at 10-20m is too much loss and not required.
If your tuner is as large or twice the size of your radio, you probably 
are on the right track.
Fire away......
73 Kees K5BCQ 