Transmission Lines
---------------------
Let me say that there's nothing special about using the
spiral electrode method with the twisted transmission line.
It's just a convenient method of adjusting the coupling to the
tube by squeezing or stretching the spirals. You could just as
easily use the braided wire and clamp method, or copper bands
around the ends of the tube as others have done.
The reason for the twisted transmission line is twofold.
First, it provides a high RF voltage at the tube just before
the tube lights up. Second, it effects an approximate impedance
transformation between the coax cable from the tuner and the
tube itself.
The balun does (or should do) the same thing, but the
winding turns ratio and the magnetic characteristics of the
ferrite core inhibit really effective high power operation of
the balun. The twisted transmission line does not suffer from
magnetic core losses or power saturation limits as does the
ferrite. It should be able to pass the modulation frequency
harmonics a bit better than will the balun, at least
theoretically, anyway.
T>It was mentioned to start with 96 and shorten from there (to
92-95"). T>What determines exact length of line?
The line, when connected to the tube electrodes, should be
resonant at about 27.12 MHz when a short circuit is connected
across the coax connector at the end of the twisted
transmission line. To measure this resonance, you need a "Grid
Dip Oscillator" (GDO), or other suitable measurement system.
OTOH, you may simply include the total length of the wire
from the coax connector at the beginning of the twisted
transmission line all the way to the tube, including the length
of whatever electrode you are using on the tube. That length
should be about 92-95 inches. It's not critical, because you
can't readily take into account things close to the tube and
the transmission line that will influence its resonant
frequency. In general, any conductive objects close to the
tube or the end of the line will lower the resonant frequency,
necessitating that the line be a bit shorter than if the tube
were clear of everything in its vicinity. Since the line will
usually build up a high enough RF voltage to fire the tube even
with 40 or 50 watts, the length is not that critical.
A Quick & Dirty test is to adjust the RF power to the tube
so that it just lights up from end to end and then bring your
hand a few inches away from one of the electrodes. If the tube
gets brighter, the line is too short. If it gets dimmer, the
line is a bit too long. NOTE - if you bring your hand too close
to the electrode, it will detune the system anyway, and the
tube will get dimmer. What you are looking for is the *first
visible change* in brightness as you move your hand closer to
the electrode. Even if you "see" the need for adjustment with
this simple test, if the tube lights satisfactorily and your
VSWR is good, the length of the line is probably OK.
Hope this helps!
Ralph
Hi Turf: saw ur msg on rife list Look on Ralphs Page how to
eliminate the balun -
(http://home.att.net/~ralph.hartwell/page0020.htm) this works
fine with an insulated box at about 92 to 96 inches overall - I
left my box open at the front but I tried to use his twisted
trans. line with out the aluminum shield & found it didn't work
until i added a lot more length to my line I had to use 146
inches in all with a 1/2 inch hardware metal screen across the
top of the tube - I have 80 inches of twisted line & 36 inches
on each end of the tube - I wraped the tube from the end into
the center with seven turns spread out to cover the tube from
each end to about 1 inch from the center - I found it lights
good on settings of 28 on my inductance, 9.5 on antenna &
transmitter on zero.(MFJ 962D antenna tuner), to start I had to
tune the antenna cap back to about center with hi power on to
start, once light all u have to do is adj the antenna to min.
swr, conductance adj. for lowest swr. Once u get the
conductance adjusted, u only have to adj. it for best swr while
running some of the Freq., also I use a 4x4 piece of aluminum
to mount my PL239 for my coax cable I also use mini 8 coax(18
ft.) between tuner & trans. line of box. Hope this helps 73s
Clellon
F>>A Quick & Dirty test is to adjust the RF power to the tube so that
F>>it just lights up from end to end and then bring your hand a few inches
F>>away from one of the electrodes. If the tube gets brighter, the line is
F>If you bring your hand too close to the electrode, aren't you risking RF
F>burns? Any suggestions as to what you can use for this quick & dirty test
F>that doesn't involve body parts? Say a screwdriver (insulated handle)?
I guess this is what comes from working with high powered RF
systems for 30+ years. A little RF here and there never
bothered me. <VBG> Seriously, we're only dealing with a couple
of hundred watts at most, unless you have a really BIG
amplifier.
Since the wire spiral is insulated with Teflon tube, I can
actually wrap my hand firmly around the spiral electrode while
the tube is in operation without getting an RF burn. All I
feel is a bit of RF diathermy heating. OTOH, if you touch the
bare wire, yes, you will get a painful RF burn. Using the point
of a common wood pencil, I can draw a 1/4 inch RF arc from the
end of the electrode while operating at 100 watts.
For the Q&D test, you need only approach the tube to a
distance of a few inches for a few seconds, so RF heating
effects are minimized, and an RF burn is unlikely, using
reasonable care.
Ralph
---
þ QMPro 1.53 þ * * * <- Tribbles ~*~ ~*~ ~*~ <- Tribbles in heaven
Even if the turns of the three inch coil are not touching, if
they are at all close, they form a coil which has
inductance..... would this not add to the reactivity of load as
seen by the linear/tuner, and would not this argue for spacing
the windings of the transmission line as far appart as
possible.... perhaps an inch or two between windings....
Perhaps it would even argue for a different winding geometry
altogether - like an infinity loop/number 8 - where the twisted
pair loops back on itself in opposing directions. This might be
better than a "coil".
Comments welcome
-David Flinn-
><< T>The extra line should be wrapped around a 3" diameter tube without
> T>touching. Ron uses 12ga teflon coated twisted pair with no external
> >>
>
>Even if the turns of the three inch coil are not touching, if they are at
>all close, they form a coil which has inductance.
**** True.
>.... would this not add to the reactivity of load as seen by the
>linear/tuner,
**** No.
>and would not this argue for spacing the windings of the transmission line
as far appart as possible....
**** No.
>perhaps an inch or two between windings....
**** No.
>Perhaps it would even argue for a different winding geometry altogether -
>like an infinity loop/number 8 - where the twisted pair loops back on
>itself in opposing directions. This might be better than a "coil".
**** Probably not.
>Comments welcome
>-David Flinn-
One of the important characteristics of a good transmission line is that
the electromagnetic fields caused by the current flow going in opposite
directions in each of the wires cancels the magnetic field to zero.
Therefore the coiled turns of transmission line do not represent a
reactance to the tuner. The common mode inductance as seen by the tuner
also cancels out provided that the turns are not too close together. On
the other hand common mode inductance serves another useful purpose. If
the plasma tube as seen by the transmission line is not perfectly balanced,
there will be an imbalance current that will flow common to both
transmission line wires in the same direction at the same time. This
current can make the equipment sensitive to touch as may be seen on the SWR
meter, and it can also interfere with the function generator. The
imbalance current plays a major roll in propagation of the RF energy which,
in my opinion, is undesirable especially in terms of RF interference.
Diverting this current to ground only enhances the RF propagation. Forming
the transmission line into a coil, now common mode inductance, will reduce
the imbalance current. Ralph's design is outstanding.
While on the subject of imbalance current from the tube and its related
connections, I am surprised that no one has suggested placing a ferrite
core on the transmission line (common mode) between the antenna tuner and
the balun transformer, whether it be internal or external to the tuner, on
the standard Bare/Rife configuration.
Domenic
<< While on the subject of imbalance current from the tube and its related
connections, I am surprised that no one has suggested placing a ferrite
core on the transmission line (common mode) between the antenna tuner and
the balun transformer, whether it be internal or external to the tuner, on
the standard Bare/Rife configuration.
Domenic >>
Why would this be desireable..... would this not reduce (supress) high
frequency RF as is commonly the case/reason for such a device and would not
this reduce all that wonderfull "harmonic" hash that everyone seems to think
is the really useful part of the signal?
Regards
-David F-
--------------------------------------
Hello Ralph & Rifers,
I have tried the no-balun setup created by Ralph and I will give my
results below my setup. (See Ralphs web site for pictures and
directions if interested)
http://home.att.net/~ralph.hartwell/rifeupd1.htm
SETUP:
Computer generated signal via Square One (Bob Hanson)
90%Ar/10%Ne tube 22" x 1" Robert Randazzo
Cobra 200xl
13.8vDC power source
Uniden 510xl with standard mods.
MFJ 948 tuner with no balun
1ft coax between CB & Amp
3ft coax between Amp and Tuner
No ground wires (don't seem to make any difference)
Tuner set on inductor L
95" of one turn per inch of insulated solid common house wire for
twisted line (had to remove the bare inner ground and strip off the
grey/white outer plastic sheath then used a drill and vise to twist
wires)
Tube wrap method is just 1/2" wide cut copper tube bent to 1/2" diameter
for snug fit over the electrode part of the tube, with a 1/4" tab for
solder to line from tuner.
The twisted pair is turned into about 7 coils at 3 inches diameter
under tube. The tube is mounted above a board and the twisted pair runs
through the wood and then splits with a "Y" shape out to solder on each
copper ring. I soldered a coax connector to the tuner end and then put
a male/male adapter to attach the wire to the tuner coax output, only
1-2" in front of the tube.
RESULTS:
Best swr's I've ever seen. I run the amp on low power and on all freqs
from 400 - 10000 I can get about 1.05 or between 1 and 1.1 gets hard to
split that 1/32" between the red lines. Nice thing is freqs don't seem
to bother the swr's anymore.
First light up on 728Hz I fooled with tuner antenna and transmitter and
got it to light, but that was the only time. All other tries I needed
to spark the tube, but could leave the tuner setting the same.
On initial running while things were just heating up I would notice the
swr's after being set at 1.0 or so would creep up within a minute and I
would have to turn the transmitter knob from 7 down toward 5 or so.
Finally once all hot I didn't have to turn anymore, this took about 5
minutes or less.
I shut things off and checked temps, CB better than it had been, amp
about the same as with balun, twisted line was very hot at the coils
just as Ralph had said, but I think the heat won't destroy the wire
covering. The best part is after running 30 minutes I could place my
hands anyplace on the tube or electrodes and it was only warm. Prior
operation would have made blisters after just 5-10 minutes.
Power out was 50watts at 400Hz, 60watts at 728Hz, 70watts at 2000Hz and
about 90 at 10000Hz, again the swr's were around 1.1 if I left tuning
alone.
OVERALL IMPRESSION:
Hard to start due to having to use sparky (peizo sparker with bare wire
1/4" apart touch tube and click). But this really isn't so hard, just
different than before. Much better operating swr's, my system with an
external 912 balun would get 1.3 to 1.5 with the same setup before the
no balun change. Power out didn't change much from before though. Tube
lights up great, but did before. I really like the "just turn on CB
with modulated input, spark the tube and your done" setup. No more
fancy tuning to light and get things started.
One note, the 1/2" electrode copper bands would get hot before with
danger of overheating but not now with the twisted wire. I did find
that swr's were very bad with a 1" or 2" wide peice of copper pipe over
the ends of tube and once I went to a small copper band 1/2" as now it
helped a lot. I was going to try the insulated felt under the copper
but I don't see any reason now due to the good operating enviornment
with the low heat at the electrode.
I was going to try to add a 3ft coax between the twisted wire and the
tuner to see what happens but I got tired and will maybe do it later.
I also may try starting tube on high power with amp and then reduce to
low power once lit to see if I can eliminate the sparky gadget.
Great work Ralph.
P.S. Ralph I got your contact info and will reply this week.
Kent
---------------------
turf's Dangerous (and dumb) Transmission Line
In the words of Monroe, "Don't do this!"
I was once happily beaming away using a transmission line made of
standard house wiring. I had not yet found suitable wire (teflon coat)
to build the twisted, coiled section near the tube, so was using the
straight house wire, and merely coiled it around 3" PVC, leaving 13" to
wrap the tube from the center. The split in the wires was within a few
mm's of the bubble.
The tuner meter indicated I was getting great power and SWRs with this
arrangement, around 125W at 1.1 SWR at high frequencies. It bothered
me that there were prominent "pearls" at many frequencies which, to me,
meant that there was not optimum efficiency.
Ron said I should at least twist the section of my 8' cable of 12 ga
wires between the tuner and the split, but when I tried this, I got
very little power output at the tube and it was very difficult to
light. But, the straight wire I was using was acting as a dipole
antenna, I was told, so I knew what I had was not ideal, even if it
appeared I was getting good output.
It would surely work better using his (and Ralph's) method of running a
coax up to a connector on the tube box, and from there doing a small
coil of, say, 14 ga wire under the tube before wrapping. The entire
length of small wire should be about 92" (+<=4"), including the wrap.
They say this works very well, but not having the teflon wire or
sleeve, I forewent this part for now.
Wanting to see if I could tune my line better, and perhaps get some of
the pearls out, I shortened it a little at a time looking for the best
length, until it got so short that it no longer worked well. No
problem, I had plenty of house wire and 259 connectors, so whipped up
another at the best length (94" for me). This one happened to have a
couple of twists before it split. A short while after I cranked the
generator, a flame shot up from a twist. Whoops. This straight line
did not like any twists.
I tried a few more things. I tried 8' of 12 ga plain hookup wire,
trying the twisted method again. Again, did not work well, so I
untwisted half of it, and it did work well, right up until the wire
insulation melted where the wires were touching within a foot of the
tube.
I then tried a cable made with 10 ga transformer (magnet) wire, but to
use this, I heat shrunk more insulation over each wire, then put them
in another heat shrink tube. This did not work well. I guessed this
was because it never heated up and on my original house wire version,
the SWRs were terrible until the wire warmed up. I tried the same
thing with 12 ga magnet wire. Tried twisting it first without
shrinking the heat shrink tube over it, to provide a spacer between the
wires. Very little power. I untwisted it and stuck it in larger
shrink tube. Like the 10ga, it did not work well, but then I was
figuring it had more to do with the way the wires were not parallel in
the tube - they were "bumpy".
Went back to the housewire. Made a cable and was careful not to let
the line twist. Fired it up, and it fired up, smoking at a point just
inside the jacket where the wires did not cross, but touched. Made
another housewire cable. This time stripped back an extra 15" from the
end of the 13" section of wire used to wrap. On the 15", covered
both wires in 27 series electrical tape (glass, high heat rated) thick,
then taped them parallel. A few seconds after I start, smoke again,
where wires are touching just inside jacket below tape.
I was thinking. What could I be doing wrong? Why did my first line
work well and these not worth a darn? I figured it out. When making
the cables, I pull out the ground which is in the center of the romex.
In the first cable I made, the paper surrounding the ground pulled out
a bit, too, and just happened to stuff the area in between the
conductors just right. I also happened to not have a twist in the
wire. I happened to not have any wires touching or too close. The
transmission line just happened to work and not catch fire.
Luckily, with the flaming transmission lines, I was quick enough at the
switch to prevent damage to any of the components besides the wires.
So, it was back to the balun for now. This did not bother me since, as
I mentioned in a recent post, I suspect that we want beams that look
good in the tube, not just good on the meter. And my beams looked
better with the balun than with my dangerous transmission line, even
though the numbers were not nearly as impressive. Seeing lots of
pearls at many frequencies with the TL bothered me since they typically
appear when the SWR is up and power is down, even though the appearance
was SWR was down and power was up.
Then, I figured it out! My transmission line was an antenna since it
did not have twists in the wire. I was not getting all the power to
the tube, I was broadcasting a lot of it. This was probably compounded
by the way I had minimal wire wrap on the tube. Without the coil (used
in good transmission line setups,) I was getting poor coupling on the
tube. Not only was my transmission line
dangerous, it was dumb.
I think this is a valuable lesson. Wrap the tube wrong and you might
get better power and SWR readings, but a less effective beam. It might
be better to have 60W at 1.5SWR than 100W at 1.1SWR if more power is
being absorbed (and retransmitted) by the tube in the 60W case. It
depends on the characeteristics of the tube/balun/wire setup. From now
on, I will go by the look of the wave and strive to get it pearl-free,
bright, and straight.
Thinking I could put some of what I had learned from working with TLs,
I tried a few different equal length methods from the balun to the
tube, but none worked as well as the setup I had before I switched.
That is 2" long (1" diam) copper sleeves soldered to 26" of 12ga
Monster cable (torn in half), with a 16 ga (transformer) wire spiraling
from one sleeve, circling at either end of the bubble and at the
opposite sleeve. I was back to my old mediocre SWR and power values,
but the wave looked good. Few pearls at any frequency. Bright beam.
Focused pretty well. Keep in mind this is for my 28" long, 80/20, 10
mm pressure, Allred bubble tube.
I shortened the 16 ga wire to make it just long enough (~40"), rather
than the 51" I was using before. I moved the sleeves around. Improved
the SWR a bit. Then, switched to Tuner setting "K" instead of "L".
Worked __great__ with this setup. SWR and power are even better than
the figures I got with my dangerous TL, and the beam looks excellent.
If I use high power on amp for low freqs, I can get at least 100W (a
lot more for high freqs) at 1.1 - 1.2 SWRs at any frequency with very
few pearls (and these are "embedded" in the beam instead of standalone)
and a bright straight beam. I can get completely pearl free at the
couple of freqs that exhibit them by dialing up to, e.g., 1.3 SWR
(instead of, say, 1.2). I think it is worth it.
I'm learning.
------------------------
For those that may be interested in having your tube setup as
Ralph Hartwell does i'd like to direct you attention towards
some good pricing! I found
http://bytemark.com/amidon/priceinfo.htm that has the teflon
tubing for 50 cents per ft. no minimum order