Date: Mon, 29 Nov 2010 16:49:42 +0000
From: Steve Hunt <steve@karinya.net>
Subject: Re: [TowerTalk] Tuners
That's a useful tuner simulation; but **DO** remember it assumes a
constant Q for the inductor. Here's how a real roller inductor Q
measures at different inductance settings on different bands:
http://www.karinya.net/g3txq/temp/rollercoaster_q.png
If you want to get meaningful loss results with that simulator, be
prepared to manually change the default Q value as you change bands and
change inductance values.
73,
Steve G3TXQ
## Per this chart, from 20-10m, the results are abysmal. The roller in
question
is a 18 uh unit, with a tapered pitch at one end. ..and uses 12 ga wire.
## a couple of point's here. Using Dr Bing's RF software for the ideal T
match
values for the low bands, say 160m, with a 50 ohm input, and a 10 ohm
resistive output,
[zero reatance], it spits out very high values for the 2 x caps, and a very
low value for the coil.
6289pf for C1 [109 volts peak, and .4 w diss]...and 4171 pf for C2.
[359 v peak and 2.6 W] Coil is 1.98 uh. With a coil Q = 125, the
coil dissipates 28 watts. I used a Q= 1200 for both caps. [1500w CXR]
## Now if we change the phase shift, and alter the value of the 3 x components,
we end up with C1= 431pf. C2= 941pf Coil = 5.71uh. Coil diss increases to
a whopping 143 watts.
## Even Palstar says their tuners are... "optimized for the lower bands"
Presumably
they mean the typ 500 pf cap has a high min C, and / or the coil is not
optimized for the
high bands.
## If you compare tuner's with the way PI or PI-L's are designed and
optimized for
linear amplifiers, you will see a big difference ! Even Henry radio figured
out this one.
Henry radio would short out 1/2 the roller coil, with a cam arrangement, when
the roller
coil was used used on the upper HF bands. A small, separate 10m coil,
usually wound using
flat strap, would be mounted at right angles to the back end of the tapered
pitch roller.
## IF a bandswitched arrangement is used, it could be better optimized.
3/8" or 1/2"
ribbon coils [or 1/4" to 3/8" tubing] could be used on 160-30m....and more
large diam
tubing could be used for 20-17-15m..and a flat strap coil for 10/12m....and
all 3 x coils at
right angles to each other. A 2-3 wafer bandswitch, with all 3 x wafers
strapped in parallel
could be used for added current capability. There is a trick to strapping
parallel wafer's in
any bandswitch. If the coil taps are done via wafer #1..... the output of the
assy must be via
wafer #2. [ or #3 if 3 x wafer's used]. This way, the RF current will
divide equally
between each wafer.
## In the above example, IF the coil Q could be increased to 250, the
power dissipated in the
coil would be 1/2. If the coil[S] were optimized better, the UN loaded Q of
the coil could be
a lot higher than 250, further reducing coil diss. In the Hb T tuner's I
have seen that used
ceramic vac caps, the limitation was still the roller coil. Even then, a 3/8"
ribbon coil fares a lot
better than using paltry 12 ga wire.
## It might be more productive to fix the ant in question, right at the
feedpoint, VS building the ultimate tuner.
Pretty simple matter to make a 80m/or 160m dipole cover both ssb/cw. Rick's
idea of shunting a cap
at the feedpoint works well, and will shift the resonance way up. Other's
have used relay switched coils
at the feedpoint instead, and that works good too.[ shifts resonance down].
Some have used motor driven
compressible coils,and that works very well, and no rolling/sliding contacts.
Later.... Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|
