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SSB antenna
Roger,
They way mine is installed is the base is secured to the transom with a standard mounting, but there is a clamp on the side of the radar arch that secures the lower portion about 6 feet above the base. No problems with excessive movement in a seaway. If you don't have an arch, them perhaps a couple of braces bay do the trick. Doug s/v Callista "Roger" wrote in message m... Doug What is the distance between the base of the antenna and the support clamp. I only have about 3 ft. Does the antenna bounce around much in rough seas. Roger "Doug Dotson" wrote in message ... Roger, We have the 23' whip and it works great. Also have a split backstay, but since the whip was on the boat when we bought it, I decided to stick with it. I'm not familiar with the 17' whip you mention. It would appear to me that you may not be abot to get good tuning acrosss the bands. The specs for the tuner say that a 23' minimum length is required if I recall correctly. Doug, k3qt s/v Callista "Roger" wrote in message om... I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. |
SSB antenna
Gary Schafer wrote in
: Ok, uncle, you win...... Everything everyone teaches is wrong, including me.... |
SSB antenna
Gary Schafer wrote in
: Ok, uncle, you win...... Everything everyone teaches is wrong, including me.... |
SSB antenna
On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer
wrote: Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. ============================================= I follow what you are saying but isn't that also the definition of resonance, i.e., the point where capacitive reactance cancels inductive reactance? |
SSB antenna
On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer
wrote: Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. ============================================= I follow what you are saying but isn't that also the definition of resonance, i.e., the point where capacitive reactance cancels inductive reactance? |
SSB antenna
On Sun, 25 Apr 2004 08:56:23 -0400, Wayne.B
wrote: On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer wrote: Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. ============================================= I follow what you are saying but isn't that also the definition of resonance, i.e., the point where capacitive reactance cancels inductive reactance? When you cancel the capacitive reactance seen at the bottom of the antenna with an equal amount of inductive reactance you see a pure resistance at the other end of the coil (transmitter end). But that does not change anything in the antenna itself. The shorter an antenna is (from a quarter wave length) the lower it's radiation resistance is. If you want to put the same amount of power into it as you did when it was longer then you must put more current into it. Just simple ohms law at this point. As long as you are dealing with pure resistance, which you are when you cancel the reactance. However, you can not use simple ohms law when dealing with a reactance, which is what Larry is trying to do. Yes there will be very high voltages at the output of the antenna tuner with a short antenna connected to it. But it is because of the reactance of the coil. That voltage is not in phase with the current at that point. Take the example that I posed to Larry about the capacitor and inductor in series connected to an AC supply. There will be a specific amount of current flowing in the circuit. You will measure a voltage across the inductor. That voltage can be much higher than the voltage from the AC supply. If you multiply that voltage by the circuit current it will appear as though you have more power in the circuit than what the AC supply is actually putting out! That looks like free energy! You have to take into account the phase shift (also called power factor) that happens across the inductor. The same thing happens with the antenna tuner situation. You can not say "because the voltage is high the current must therefore be low", like Larry wants to do. The voltage is high and so is the current. BUT THEY ARE NOT IN PHASE. There are extremely high currents in the system. The high current in the coil is what causes I squared R loss (power lose). In the information in my other post about short antennas, the coil has a resistance of around 10 ohms and the radiation resistance of the short antenna was only .3 ohms. So you can see that the coil will suck up most of the power. That is why a short antenna is less efficient than a longer one. Not because a short antenna radiates poorer than a longer one. An antenna will radiate just as well if it is resonant or not. Provided you get the same amount of power to it. The E field and H field of an antenna aren't necessarily the same. They do balance themselves out as they propagate in free space. Has nothing to do with how well it radiates. Regards Gary |
SSB antenna
On Sun, 25 Apr 2004 08:56:23 -0400, Wayne.B
wrote: On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer wrote: Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. ============================================= I follow what you are saying but isn't that also the definition of resonance, i.e., the point where capacitive reactance cancels inductive reactance? When you cancel the capacitive reactance seen at the bottom of the antenna with an equal amount of inductive reactance you see a pure resistance at the other end of the coil (transmitter end). But that does not change anything in the antenna itself. The shorter an antenna is (from a quarter wave length) the lower it's radiation resistance is. If you want to put the same amount of power into it as you did when it was longer then you must put more current into it. Just simple ohms law at this point. As long as you are dealing with pure resistance, which you are when you cancel the reactance. However, you can not use simple ohms law when dealing with a reactance, which is what Larry is trying to do. Yes there will be very high voltages at the output of the antenna tuner with a short antenna connected to it. But it is because of the reactance of the coil. That voltage is not in phase with the current at that point. Take the example that I posed to Larry about the capacitor and inductor in series connected to an AC supply. There will be a specific amount of current flowing in the circuit. You will measure a voltage across the inductor. That voltage can be much higher than the voltage from the AC supply. If you multiply that voltage by the circuit current it will appear as though you have more power in the circuit than what the AC supply is actually putting out! That looks like free energy! You have to take into account the phase shift (also called power factor) that happens across the inductor. The same thing happens with the antenna tuner situation. You can not say "because the voltage is high the current must therefore be low", like Larry wants to do. The voltage is high and so is the current. BUT THEY ARE NOT IN PHASE. There are extremely high currents in the system. The high current in the coil is what causes I squared R loss (power lose). In the information in my other post about short antennas, the coil has a resistance of around 10 ohms and the radiation resistance of the short antenna was only .3 ohms. So you can see that the coil will suck up most of the power. That is why a short antenna is less efficient than a longer one. Not because a short antenna radiates poorer than a longer one. An antenna will radiate just as well if it is resonant or not. Provided you get the same amount of power to it. The E field and H field of an antenna aren't necessarily the same. They do balance themselves out as they propagate in free space. Has nothing to do with how well it radiates. Regards Gary |
SSB antenna
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SSB antenna
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