The newest Update Information will always be found at the top of this update page.
NOTE: Before reviewing the material on this page, it will be helpful to have looked over the information I have presented on my Rife Unit page, along with viewing the pictures detailing the manner in which I have constructed my unit. The data on this update page shows only the changes I have made to the system as shown on the previous page.
11/30/97 - HOW TO ELIMINATE THE BALUN
This Section Was Last Updated 11/10/00
Tests I have made during the last two days have shown that it is possible to eliminate the balun from the Rife/Bare unit by using a modified transmission line RF feed system between the antenna tuner and the tube. This results in improved ease of tuning the system, with the VSWR readings reaching lower values, and remaining at low levels regardless of the modulating frequencies applied to the CB transmitter.
What is the reason for the balun anyway? It is used is to perform an effective transfer of the RF energy from the amplifier to the tube. Unlike an antenna or a resistor load, a gas discharge tube represents a dynamic load, containing varying resistive and reactive components. The tube also requires a much greater RF voltage to cause the gas in the tube to initially "turn on" and begin emitting light than it does to maintain the discharge in the gas after the tube is lighted.
The balun, by acting as a step-up transformer, raises the RF voltage present at the tube to a higher level than the amplifier is able to provide on its own. This enables the tube to start more easily. It also serves to convert the unbalanced (single wire above ground potential) coaxial cable feed to a balanced 2-wire (both lines at an equal voltage but opposite polarity above ground potential) feed which can be connected directly to the Rife/Bare tube.
The real problem with feeding RF power to the tube is that the tube exhibits a high impedance state (Hi-Z) when it is off, and a low impedance state (Lo-Z) when it is on. Obviously, we cannot adjust our antenna tuner for both conditions at once, so we must do something else to handle this problem. In order to start the tube, (High Z state) we need a high RF voltage with very little current. However, after the tube lights (Low Z state) we need a lower voltage but at a higher current.
To solve this quandary, we may make use of the fact that an open ended 1/4 wavelength transmission line will exhibit a very high impedance at the open end, while at the same time, 1/4 of an electrical wavelength back down the line in the direction of the RF amplifier, the line will exhibit a low impedance. If RF power is applied to the end of this line which is connected to the RF amplifier, a very high RF voltage will appear on the open end of the line. If the open end of the transmission line is then terminated in its characteristic impedance, the voltage will drop to normal, and the line will then deliver power to the load normally.
We will place the open end of this quarter wavelength transmission line against our R/B tube. The high voltage present on the transmission line just before the tube lights will trigger the tube, and as soon as the tube fires, it will be able to draw power from the amplifier normally.
We may make an assumption that the tube represents about a 1200 ohm load. We know that the RG-8 coax is 50 ohms impedance. According to transmission line theory, we can effectively match these impedance values by using 1/4 wavelength of transmission line which has a characteristic impedance of about 250 ohms. It just so happens that the twisted wire line I will describe in this article, has an impedance of about 250 ohms.
When the tube is off and the RF power first comes on at the beginning of each modulation cycle, the tube end of the line is effectively open circuited (no load) because the gas in the tube is not ionized. Due to the impedance transformation characteristics of an open ended quarter wavelength transmission line, the RF voltage present from the amplifier is stepped up to a very high value by the action of the transmission line as described above. This results in a severe mismatch on the amplifier, with a VSWR of probably 20:1 or more. However, in reality the power actually flowing down the line at this point is in the milli-watt region, so no damage is done to anything in the system.
The high RF voltage present at the end of the transmission line ionizes the gas inside the tube. The ionized gas column then conducts the RF power very well, and presents a low impedance load to the line, tuner, and amplifier. Since this is the condition where the unit must deliver the power to the tube, we simply adjust the tuner for the "tube-on" condition, i.e., carrier on and no modulation. Using this tuner setting ensures that the maximum power will be delivered to the tube whenever it is lit. This also means that there will exist a serious mismatch when the tube is off, but, as pointed out above, this will do no harm since the power flowing at that time is minimal. It also means that you will see very little VSWR change as you modulate the unit through various audio frequencies, or at least until you get high enough in frequency so that the filtering action of the antenna tuner starts to restrict some of the sideband energy present in the square wave.
Essentially, using a transmission line in this manner ensures that no matter what the tuner settings are, a high RF voltage will be delivered to the tube to start it reliably.
Radio Frequency Transmission line theory says that a quarter wavelength in free space (where the RF signal is radiating through the air or a vacuum) is about 109 inches when calculated at a frequency of 27.12 MHz. If the RF signal travels down a wire, it slows down slightly. If the wire is surrounded by insulation, the velocity of propagation (VP) becomes even slower. If we consider that the speed of travel (VP) of the RF signal through free space has a value equal to 1, than we may assign a value to VP for any case where the speed of travel is less than 1.
The chart below shows the relation of measured values of VP to various conditions for transmission lines:
|Conditions||Type of Insulation||Velocity of Propagation||To Calculate 1/4 Wavelength in inches:||1/4 Wavelength @ 27.12 MHz|
||Vacuum||1.00||2953 / F MHz||109|
|Bare Wire, Straight||Vacuum or Air Only||0.98 - 0.95||2850 / F MHz||105|
|Insulated Wire, Tightly Twisted||TFE / Teflon||0.70||2079 /F MHz||76.7|
|Insulated Wire, Tightly Twisted||PVC / THHN||0.52||1530 /F MHz||56.4|
This chart dramatically illustrates that when the wires are covered with insulation and twisted together, the effective speed of RF transmission slows down considerably. This allows us to construct a matching system which uses fairly short lengths of wire. Coiling this wire into a spiral allows a compact design. For my design, I chose to use Teflon insulation because of its heat resistance and excellent electrical properties at 27 MHz.
Construction of the Twisted Transmission Line
The twisted parallel wire transmission line is made with two lengths of #12 bare copper wire. each piece being about 90 inches long. Since the wire will shorten up a bit as it is twisted, we must allow some extra to accommodate this shortning. This length also allows about 4 inches on each end for clamping and working with the wire. The finished line will be cut to a length of about 77 inches.
Both of the two pieces of copper wire are covered with sections of Alpha Wire Company type TFT-200 (#11) Teflon tubing. Round off the cut ends of the wire slightly so that it does not snag the Teflon tube as you slide it onto the wire. It's a close fit, but Teflon is very slippery stuff, so it will go on the wire fairly easily.
After tightly fastening one end of each of the two Teflon covered wires in a bench vise, chuck the free ends into a portable electric drill and wind 'er up until the wires have about 1 to 1/2 twists per inch. You need to hold on to the drill because that heavy wire will try to twist back quite a bit.
Next, untwist the wires at one end of your completed twisted transmission line for about 3 inches. Cut about an inch of the Teflon tube off of both of the wires so you can fasten them to the coax connector which you have mounted on the metal plate or your tube enclosure. Untwist enough of the wires at the other end of the line so that you can spread the wires apart and solder them to the ends of the spiral electrode windings which you have wound around the ends of your tube. This is much easier and less hazardous to the health of your tube than trying to make the line and spiral electrodes in one piece.
You may wind the completed transmission line into a coil about 3" or larger in diameter to save space. If you do this, it is necessary to separate the turns of the coil about equal to the diameter of the twisted line itself.. This is necessary, because if the line is too close to itself in the spiral, the RF energy will interact unfavorably between the turns and result in tuning problems. More spacing is much better than too little!
The wire work hardens when you twist it and wind it, so it will be hard to handle. The up side of that is that after you get it connected to the connector and the tube, it will stay there without much of any other support.
Note that winding the line onto a coil is not absolutely necessary, but it is very convenient. The line can be formed into a straight line, or a square, an "S", or a "U" configuration. Since this system does not use a balun, the currents in the line are somewhat unbalanced. As a result, the line will radiate somewhat if it is straight and in the open. If the line is formed into a coil, the radiation cancels out fairly well, so that more of the RF power will get to your tube than if the line is operated while it is straightened out.
Take a look at the finished Coiled Transmission Line system as installed in my shielded tube enclosure. Also, take a look at the modified Electrode Spiral on my tube.
Since the coax cable enters the enclosure through a metal wall, this ensures that the twisted transmission line "starts" at the metal wall. This reduces unwanted RF radiation and helps the line produce the highest RF voltage at the tube.
If you choose not to use a shielded enclosure, you may need to adjust the length of the twisted transmission line for best results (highest voltage at the tube = easiest starting of the tube.) Another alternative is to mount your tube a few inches above a large metal plate. Mount the tube on insulating standoffs such as the one which is shown here > This is the finished support. Feed the RF signal from the amplifier through the metal plate, preferably with a coax connector mounted at the center of the plate, and connect the twisted transmission line between the coax connector and the tube electrodes.
Here's how it's all hooked up:
From the antenna tuner, I have RG-8 coax cable coming from one of the coax output connections on the tuner. The RG-8 then goes directly to the connector on the rear of the tube enclosure. I have tried various coaxial cable lengths between 2 feet and 20 feet, and they all work just fine. The tuner will need to be retuned slightly for any change in transmission line length. You normally want the cable to be as short as possible, as some of the power is lost in it due to the very high RF currents flowing in the coax. These occur due to the high VSWR existing between the tuner and the tube.
After replacing the balun with my twisted transmission line, I find that I can now light almost the entire length of my 30" long tube with just 10 watts of RF output directly from the CB. I can also swing the antenna tuner capacitors from one extreme to the other and the tube stays lit. I can also turn the inductor about +/- 3 turns and still keep the tube lit. Gating the modulation to tube on and off is now easy; the tube lights every time, without fail. The transmission line does get warm, especially where it is connected to the coax connector as it comes into the tube enclosure.
The RF losses appear to be less than they were with the balun. It also eliminated the overheating of the balun which caused system shutdown after about 40 minutes of operation due to the balun ferrite material overheating enough to lose its normal magnetic characteristics.
Another more serious problem also vanished. Before, when using the ferrite core balun, it was possible to have the tube go out but still have the forward power meter show a large amount of RF power going to the balun. This condition apparently would drive the ferrite core of the balun into non-linear operation and cause severe core heating of the balun. This heating can fracture the core and ruin the balun for further use. My Twisted Transmission Line, having no ferrite core, cannot fail in this manner.
As a further test to verify that this system is reproducible, a second twisted transmission line section was constructed and attached to a Randazzo Bubble Tube measuring 20" overall length. 6-turn spiral electrodes were wound over each end of the tube for a distance of about 2 inches. Here's a picture of the tube running at Low Power while it is laying on a chair outside of the enclosure. Tuning and operating results were very similar to my 30" tube operating in the shielded enclosure.
11/27/97 - OPTICAL TESTS
I built an optical detector unit (a "NanoMeter Receiver") consisting of a photo diode which is sensitive throughout most of the IR and visible light region, a 7 element optical system, and an oscilloscope.
The detector diode has a flat frequency response from DC to over 1 MhZ. A 62mm focal length f1.2:1 Angenieux lens (designed to pass IR as well as visible light) is used to gather the light from the device under test. (The R/B tube) When this lens is combined with the built in lens on the diode package, the resulting optical system forms a 20X telescope. This design allows me to separate the detector unit from the R/B tube by 10 feet or more and still obtain a strong signal. When used at a distance of 6 feet from the tube, it allows me to analyze the signal from as small an area as a 2" long section of the tube. The unit is mounted on a tripod with a pan head for ease in adjustment.
The output of the diode is then connected to one channel of a dual trace Textronix oscilloscope for analysis. The other channel of the oscilloscope was connected to the RF signal driving the R/B tube for comparison.
I observed that the output optical waveform is not a square wave, even though the RF signal to the tube is a square wave pulse of RF energy. There is a large optical spike at the beginning of each "light cycle" just as the RF signal "hits" the tube.
This pulse is about 6 times the amplitude of the "normal" optical square wave itself. The spike rapidly decays to the "normal" optical square wave amplitude and remains there until the RF is turned off. At the end of the RF pulse, the optical signal rapidly decays to zero until the start of the next pulse.
The amplitude of the spike varies between 7x and 3x of the normal optical square wave signal level. I have only observed this optical spike at modulation frequencies below 20,000 Hz. It appears at all power levels fed to the tube, from 10 watts to 200 watts. The adjustment of the antenna tuner has a definite effect on the amplitude of the spike. This optical spike is visible from a tube containing a 90/10 Argon/Neon mixture, as well as a 100% Argon tube. Interestingly enough, a smaller tube I have containing Mercury and Argon does not show this spike at any frequency. Further research is needed to see what causes this optical spike, and if it is detrimental to, or necessary for, the proper operation of a Rife/Bare tube system.
It may be that energy is "pumped" into the gas molecules prior to their ionization by the RF field, and that when they begin to glow, they release much of the pumped energy in a burst of light. I have observed that the optical signal is delayed for about 75 Usec after the RF pulse first gets to the tube.
Want to look at some oscilloscope pictures? Here they are > Scope Pictures, RF & Optical Waveforms
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