From: Jeffdeham ([email protected]) Subject: How does the rainbow tuner work? I was looking at the rainbow tuner which matches a half wave end fed antenna to 50 ohms using a quarter wave radial. I am guessing it works like a transformer but not sure. Here is the schematic; Ant |----- quarter wave radial | | | GND ---------- | ) --- ) Variable )<----- 50 ohm --- ) | ) | ) ---------- | GND If it does work like a transformer how does it do it? How is the matching done? Thanks for any help! Jeff Post a follow-up to this message Message 2 in thread From: Dale Parfitt ([email protected]) Subject: Re: How does the rainbow tuner work? Jeffdeham wrote: > I was looking at the rainbow tuner which matches a > half wave end fed antenna to 50 ohms using a quarter > wave radial. I am guessing it > works like a transformer but not sure. Here is > the schematic; > > Ant |----- quarter wave radial > | | > | GND > ---------- > | ) > --- ) > Variable )<----- 50 ohm > --- ) > | ) > | ) > ---------- > | > GND > > > If it does work like a transformer how does it do it? > How is the matching done? > > Thanks for any help! > > Jeff The antenna represents a hi impedance- in the 2K-->4K range for HF and wire as a radiator. The parallel tank L-C is also a hi impedance. The coaxial cable then is tapped up from ground until the 50 Ohm point is reached. Dale W4OP Post a follow-up to this message Message 3 in thread From: Jeffdeham ([email protected]) Subject: Re: How does the rainbow tuner work? Dale Parfittwrote in message > > If it does work like a transformer how does it do it? > > How is the matching done? > The antenna represents a hi impedance- in the 2K-->4K range for HF and > wire as a radiator. The parallel tank L-C is also a hi impedance. The > coaxial cable then is tapped up from ground until the 50 Ohm point is > reached. That makes perfect sense except if you have two high impedances in series how does tapping the coil at a certain point give you 50 ohms? What exactly is the process where by the impedance transformation occurs? Just trying to learn here. Thanks for any help once again! Jeff Post a follow-up to this message Message 4 in thread From: 'Doc ([email protected]) Subject: Re: How does the rainbow tuner work? Jeff, Series? How about parallel. 'Doc Post a follow-up to this message Message 5 in thread From: Cecil Moore ([email protected]) Subject: Re: How does the rainbow tuner work? Jeffdeham wrote: > That makes perfect sense except if you have two high impedances in > series how does tapping the coil at a certain point give you 50 ohms? > What exactly is the process where by the impedance transformation > occurs? It is NOT two high impedances in series. It is an autotransformer action related to the turns ratio. All impedances are referenced to ground at the bottom of the tuned circuit. In a high-Q circuit, the impedance at the top of the tuned circuit will be the impedance presented by the antenna. So as you "tap down" on the coil, the impedance goes from a few thousand ohms to zero. At some point in the transformer tap down process, you will encounter a point where the ratio of the voltage to current is 50 ohms. That's where to attach the 50 ohm coax for a low SWR and good efficiency. -- 73, Cecil http://www.qsl.net/w5dxp ifferent Servers! =----- Post a follow-up to this message Message 6 in thread From: Irv Finkleman ([email protected]) Subject: Re: How does the rainbow tuner work? Jeffdeham wrote: > > I was looking at the rainbow tuner which matches a > half wave end fed antenna to 50 ohms using a quarter > wave radial. I am guessing it > works like a transformer but not sure. Here is > the schematic; > > Ant |----- quarter wave radial > | | > | GND > ---------- > | ) > --- ) > Variable )<----- 50 ohm > --- ) > | ) > | ) > ---------- > | > GND > > > If it does work like a transformer how does it do it? > How is the matching done? > > Thanks for any help! > > Jeff The fed end of a half wave antenna appears as a high impedance. The parallel resonant circuit (at resonance) also appears as a high impedance. To match the low impedance of the feedline, it is necessary to tap down on the coil (so as to feed between the tap and ground) -- like an autotransformer. Think of a half wave dipole -- you need good insulators on the end of the half wave because the voltage there is very high, and the current is very low. Uzing (pardon the pun) Z=E/I=High/Low yields a high impedance. This is a pretty simplified explanation, but if you think about it it will work. Hope it helps you to understand things a bit. Irv VE6BP -- Post a follow-up to this message Message 7 in thread From: Jeffdeham ([email protected]) Subject: Re: How does the rainbow tuner work? Irv Finkleman wrote in message news:<[email protected]>... > Think of a half wave dipole -- you need good insulators on the end > of the half wave because the voltage there is very high, and the > current is very low. Uzing (pardon the pun) Z=E/I=High/Low yields > a high impedance. > > This is a pretty simplified explanation, but if you think about > it it will work. > > Hope it helps you to understand things a bit. I have a much better understanding of how it all works now. I had an idea that is how it would work but just couldn't visualize it. Been 27 years since electronics school and the old brain has gotten a little fuzzy since then! 8-) Thanks everyone for all your help! 73! Jeff Post a follow-up to this message Message 8 in thread From: Reg Edwards ([email protected]) Subject: Re: How does the rainbow tuner work? If the feedpoint resistance of the 1/2-wave vertical is R ohms, then the input impedance of the coil tapping point is R*(K squared) where K is the fraction of total coil turns below the tap. It requires only that L and C are resonant at the same resonant frequency of the 1/2-wave antenna. A roller inductor makes a nice job of it. Disadvantage - the roller inductance L being fixed, with C, limits the matching range to only 1 or 2 bands before things become inefficient. For highest efficiency L should be big and C should be quite small like 10 to 50pF. Solution - prune the antenna to an off-resonance frequency. I have a program for it but never published it because its too simple. --- Reg G4FGQ. Post a follow-up to this message Message 9 in thread From: Bud Rogers ([email protected]) Subject: Re: How does the rainbow tuner work? Jeffdeham wrote: > I was looking at the rainbow tuner which matches a > half wave end fed antenna to 50 ohms using a quarter > wave radial. I am guessing it > works like a transformer but not sure. Here is > the schematic; > > Ant |----- quarter wave radial > | | > | GND > ---------- > | ) > --- ) > Variable )<----- 50 ohm > --- ) > | ) > | ) > ---------- > | > GND > > > If it does work like a transformer how does it do it? > How is the matching done? I'm not familiar with the rainbow tuner, but if I read your schematic right, the tapped coil functions as an autotransformer. Autos are commonly used as step-up and step-down transformers in power substations. A functional equivalent using separate windings would look like this. | | | ---------------- | ) | ) | ) ----- ) ----- ) ( <----------- 50 ohm | ) ( | ) ( | ) ( ----------------------------------- | GND 73 de KD5SZ Post a follow-up to this message Message 10 in thread From: Bud Rogers ([email protected]) Subject: Re: How does the rainbow tuner work? View this article only Newsgroups: rec.radio.amateur.antenna Date: 2003-09-08 16:28:21 PST Bud Rogers wrote: | | | ----------------------- | ) | ) | ) ----- ) ----- ) ( <----------- 50 ohm | ) ( | ) ( | ) ( ----------------------------------- | GND 73 de KD5SZ �2003 Google Message 11 in thread From: Jeffdeham ([email protected]) Subject: Re: How does the rainbow tuner work? Bud Rogers wrote in message news:<[email protected]>... > Bud Rogers wrote: > Gak. I screwed that up. Let's see if this comes out any better. > > | > | > | > ----------------------- > | ) > | ) > | ) > ----- ) > ----- ) ( <----------- 50 ohm > | ) ( > | ) ( > | ) ( > ----------------------------------- > | > GND That's more or less how I thought it worked but just couldn't visualize it. If you could answer yet another question. How does a autotransformer work exactly? I can see how you can tap up and down the coil to hit a certain point where you can a 50 ohm match. But when I look at the schematic all I see is a coil in parallel with a variable cap. How does the autotransformer in essence become a transformer? Or rather how does it become the above schematic? Thanks! Jeff Post a follow-up to this message Message 12 in thread From: Bud Rogers ([email protected]) Subject: Re: How does the rainbow tuner work? Jeffdeham wrote: > If you could answer yet another question. How does a autotransformer > work exactly? I can see how you can tap up and down the coil to hit a > certain point where you can a 50 ohm match. But when I look at the > schematic all I see is a coil in parallel with a variable cap. How > does the autotransformer in essence become a transformer? Or rather > how does it become the above schematic? That amounts to two questions that aren't necessarily related. One is how an autotransformer works, the other is how inductance and capacitance can be combined to match an antenna to a feed line. I'll take a stab at the first question. Think about how a transformer works. If you place two inductances in close proximity, a magnetic field induced in one will induce a current or voltage in the other. By selecting the proper turns ratio between the two inductances, you can transform an AC voltage or current up or down. You can transform high voltage/low current to low voltage/high current or vice versa. Which is another way to say you can transform impedance. In an autotransformer the same principles apply, but a portion of the inductance is common to both circuits. A voltage applied across the tapped portion of the coil will produce a higher voltage across the whole coil. A voltage applied across the entire coil will produce a proportionately lower voltage across the tapped portion. The current in the tapped portion will be the sum of the currents flowing in the two circuits. Not good if you need isolation, but not an issue if all you want is to transform voltage, current, or impedance. Does that make sense? On the second question you might be better off to read the antenna matching chapter in any Radio Amateurs Handbook. :} 73 de KD5SZ Post a follow-up to this message Message 13 in thread From: Caveat Lector ([email protected]) Subject: Re: How does the rainbow tuner work? Another good reference is at ARRL Site URL: http://www.arrl.org/tis/info/pdf/9401070.pdf Titled "Do You Need An Antenna Tuner" 73 From The Signal In The Noise Caveat Lector Ya All Back