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Matching Issue ........... I think!
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Matching Issue ........... I think!
Cecil Moore wrote:
wrote: the physical antenna stays as is and works extremely well on 75. What has me asking the questions is that I was told a 1/4 wave piece of coax would get it to work on 40. Was that a parallel stub by any chance? hmmmm, thats not what I recall being told but would it work? one feed line? -- I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!! |
Matching Issue ........... I think!
Richard Clark wrote:
On Thu, 01 Feb 2007 19:32:05 -1000, wrote: signal reports on 80 have been very impressive. You sound like a very good customer prospect weighed against the testimonials offered to a German inventor of a 9 foot tall 160M radiator. Signal reports on 80 still doesn't make it work on 40M however. The reasons have been explained for your difficulties, and solutions offered. Are you looking for something different? 73's Richard Clark, KB7QHC Richard, I am not trying to be an ass here, but I was told BEFORE the antenna was built it would work on 40. So it got built and doesnt work on 40 as is. It was suggested at the time to use a 1/4 wave section of coax to get it to work on 40, which as you know it doesnt. All I want to do is figure out a way to get it to work on 40 now. Believe me this antenna works extremely well on 80. 20 over 9 reports from ZL when the VK's there are only 10 over 9. This configuration works well, I am sure someone could build a similar version just for 40 and be a big gun on 40. -- I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!! |
Matching Issue ........... I think!
On Fri, 02 Feb 2007 05:59:56 -1000, wrote:
I was told BEFORE the antenna was built it would work on 40. You are a victim of poor information. That is evident in the false assurance (it simply doesn't make sense) and the positive proof of your measurements. So it got built and doesnt work on 40 as is. No one here is surprised by that outcome. It was suggested at the time to use a 1/4 wave section of coax to get it to work on 40, which as you know it doesnt. A quarter wave solution was offered by Owen which was the correct solution. This does not mean it would turn a dog into a performer, it simply meant it would match. Now, as to the matter of making it match using coax, THAT is a hash pipe dream. You may eventually succeed through luck and happenstance, but chances are that coax will glow at night. All I want to do is figure out a way to get it to work on 40 now. As I offered, Owen has already done the work, but only you can build it and discover it works. Believe me this antenna works extremely well on 80. 20 over 9 reports from ZL when the VK's there are only 10 over 9. That's nice, but it doesn't solve 40M. 73's Richard Clark, KB7QHC |
Matching Issue ........... I think!
Cecil Moore wrote:
wrote: hmmmm, thats not what I recall being told but would it work? one feed line? A shorted 1/4WL 80m parallel stub will yield a high impedance on 80m and a low impedance on 40m. This is sometimes used with open-wire line to achieve a match on both bands for a dipole that is 1/2WL on 80m and 1WL on 40m. Also to open up a 1WL 40m loop for use on 80m as a 1/2WL dipole. I have seen this before, but somehow I would have to be able to connect and unconnect the stub. -- I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!! |
Matching Issue ........... I think!
wrote:
Cecil Moore wrote: wrote: hmmmm, thats not what I recall being told but would it work? one feed line? A shorted 1/4WL 80m parallel stub will yield a high impedance on 80m and a low impedance on 40m. This is sometimes used with open-wire line to achieve a match on both bands for a dipole that is 1/2WL on 80m and 1WL on 40m. Also to open up a 1WL 40m loop for use on 80m as a 1/2WL dipole. I have seen this before, but somehow I would have to be able to connect and unconnect the stub. No you don't. The stub is a high impedance on 80m in parallel with a low feedpoint impedance and therefore has a negligible effect on 80m. It can be left in the circuit. The stub is a low impedance on 40m in parallel with a high feedpoint impedance which lowers the SWR and makes your transmitter happy. On 40m, the stub acts as a low impedance load that eventually delivers most of its stored energy to the high impedance antenna (assuming the stub is made from low-loss transmission line). -- 73, Cecil http://www.w5dxp.com |
Matching Issue ........... I think!
In message , Cecil Moore
writes I have seen this before, but somehow I would have to be able to connect and unconnect the stub. No you don't. The stub is a high impedance on 80m in parallel with a low feedpoint impedance and therefore has a negligible effect on 80m. It can be left in the circuit. The stub is a low impedance on 40m in parallel with a high feedpoint impedance which lowers the SWR and makes your transmitter happy. On 40m, the stub acts as a low impedance load that eventually delivers most of its stored energy to the high impedance antenna (assuming the stub is made from low-loss transmission line). I don't understand that, Cecil. Yes, the stub will be a halfwave on 40m, and therefore add a low impedance in parallel with the antenna feedpoint. Depending on the exact resonant length of the stub, the impedance will be either a very low value resistor, a low value inductor, or a large value capacitor. None of these is going to help to convert the resistive part of the input impedance of the antenna to something around 50 ohms. However, I suspect that what the matching arrangement actually consists of a stub which is connected across the feeder AT SOME DISTANCE from the antenna feedpoint. If the antenna feedpoint presents a high impedance on 40m, there will be a point at some distance (less than a quarterwave) back along the feeder (towards the TX) where the resistive part of the impedance (at that point) is 50 ohm, in parallel with a considerable capacitive reactance. By choosing the correct length of stub and the correct distance between the connection of the stub and the antenna feedpoint, you can probably get a 'reasonable' match for both 80m and 40m. If this IS the actual physical arrangement, it's time to get the Smith Charts out! Ian. -- |
Matching Issue ........... I think!
Ian Jackson wrote:
I don't understand that, Cecil. Yes, the stub will be a halfwave on 40m, and therefore add a low impedance in parallel with the antenna feedpoint. Depending on the exact resonant length of the stub, the impedance will be either a very low value resistor, a low value inductor, or a large value capacitor. None of these is going to help to convert the resistive part of the input impedance of the antenna to something around 50 ohms. You're right, Ian. I was trying to apply the same principles that causes the stub to turn a full-wave 40m loop into a 1/2WL 75m dipole and had a senior moment. But that idea would work with RG-174. With a 3 dB loss in the stub, the impedance looking into the stub would be around 50 ohms. :-) -- 73, Cecil http://www.w5dxp.com |
Matching Issue ........... I think!
In message , Cecil
Moore writes Ian Jackson wrote: I don't understand that, Cecil. Yes, the stub will be a halfwave on 40m, and therefore add a low impedance in parallel with the antenna feedpoint. Depending on the exact resonant length of the stub, the impedance will be either a very low value resistor, a low value inductor, or a large value capacitor. None of these is going to help to convert the resistive part of the input impedance of the antenna to something around 50 ohms. You're right, Ian. I was trying to apply the same principles that causes the stub to turn a full-wave 40m loop into a 1/2WL 75m dipole and had a senior moment. But that idea would work with RG-174. With a 3 dB loss in the stub, the impedance looking into the stub would be around 50 ohms. :-) I'm not an antenna person, Cecil. Are you going to do the hono(u)rable thing and calculate the dimensions? Ian -- |
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