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#1
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vert antenna construction
I am looking to use a piece of PVC as the center insulator of a vertical
dipole I'm planning to put up. Anyone know the insulating characteristics of this stuff? It's not going to conduct significantly @ hf when wet?? Thanks for the help. gary |
#2
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"Angela & Gary" wrote in message ... I am looking to use a piece of PVC as the center insulator of a vertical dipole I'm planning to put up. Anyone know the insulating characteristics of this stuff? It's not going to conduct significantly @ hf when wet?? Thanks for the help. gary It works fine. I used a short piece of pvc to connect 2 pieces of aluminum conduit. I fed the coax thru one end of the alum conduit to have a vertical dipole fed from inside where the 3 pieces come together |
#3
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On Sat, 19 Feb 2005 13:14:55 -0800, Angela & Gary
wrote: I am looking to use a piece of PVC as the center insulator of a vertical dipole I'm planning to put up. Anyone know the insulating characteristics of this stuff? It's not going to conduct significantly @ hf when wet?? Thanks for the help. gary It will work great. If you want to test it, microwave a piece of the material for 1 minute. IF it gets very warm, you may want a different material. The white pvc should work as well as you need and then some. -- 73 for now Buck N4PGW |
#4
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I'd also add a glass of water in the microwave when you do
that...I'm not sure if they are still that way, but it used to be bad for them to run with no load...IE: food...MK |
#5
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It's not clear to me how you correlate how warm something gets in the
microwave oven with how much loss it'll incur at the end of an HF antenna. Maybe someone can explain this. Roy Lewallen, W7EL wrote: I'd also add a glass of water in the microwave when you do that...I'm not sure if they are still that way, but it used to be bad for them to run with no load...IE: food...MK |
#6
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On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen
wrote: It's not clear to me how you correlate how warm something gets in the microwave oven with how much loss it'll incur at the end of an HF antenna. Maybe someone can explain this. Roy Lewallen, W7EL The microwave works with RF to heat the 'food'. If an object absorbs RF, it does so as heat, therefore, if you subject it to intense RF by using a microwave oven, it will heat up. If it heats up, it is affecting the antenna's radiation. Depending on how it is connected to the antenna and type of antenna, it may not make a noticeable difference on the signal, but in many cases, especially where the wire is running along with or inside of a material such as PVC, the material may have a detrimental impact on the signal or SWR. Not being aware of this a long time ago, I built a two meter half-wave vertical dipole by dropping a line of wire into a piece of CPVC and capping it off. My mobile 5/8 wave whip on the car, twelve feet below it, using the same rig has much much better reception and signal than the dipole. I plan to replace that antenna with a similar dipole using 1/2 inch copper tubing. When I nuke the cpvc for one minute, it gets warm to the touch. I don't expect to melt it using my 706, but I do have a couple of repeaters I can't hear from that antenna that I would like to reach. 73 for now Buck N4PGW -- 73 for now Buck N4PGW |
#7
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On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen
wrote: It's not clear to me how you correlate how warm something gets in the microwave oven with how much loss it'll incur at the end of an HF antenna. Maybe someone can explain this. Dear Roy, Perhaps that is not the objective, Roy - maybe the rationale' is simply to decide whether or not a particular sample of material is a "high loss" dielectric or not. Regards, Bob, W9DMK, Dahlgren, VA Replace "nobody" with my callsign for e-mail http://www.qsl.net/w9dmk http://zaffora/f2o.org/W9DMK/W9dmk.html |
#8
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Bob, W9DMK wrote:
"-maybe the rationale is simply to decide whether or not a particular sample of material is a "high loss" or not." I think that`s it. The properties of dielectrics are functions of temperature and frequency. My CRC Handbook of Chemistry and Physics shows PVC`s dielectric constant is definitely a function of frequency, unlike polystyrene and some other pastics. I`ve seen PVC used as a base insulator for vertical elements of a HF antenna array, and it worked OK. I think low power factor and dissipation=A0are desirable for an insulator. My 1987 edition of the ARRL Handbook has a table 47 on pages 35-36 and 35-37 titled "Properties of Common Thermoplastics. Maybe later editions have expanded tables. Best regards, Richard Harrison, KB5WZI |
#9
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Buck wrote:
On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen wrote: It's not clear to me how you correlate how warm something gets in the microwave oven with how much loss it'll incur at the end of an HF antenna. Maybe someone can explain this. Roy Lewallen, W7EL The microwave works with RF to heat the 'food'. If an object absorbs RF, it does so as heat, therefore, if you subject it to intense RF by using a microwave oven, it will heat up. If it heats up, it is affecting the antenna's radiation. No, that's not correct. If you heat up an object in the microwave oven, it indicates that an object of that material, size, and shape absorbs some fraction (how large a fraction, you have no idea) of energy when an intense microwave field is applied. It says nothing about what that object will do when put at the end of an HF antenna, where it isn't exposed to an intense microwave field. Depending on how it is connected to the antenna and type of antenna, it may not make a noticeable difference on the signal, but in many cases, especially where the wire is running along with or inside of a material such as PVC, the material may have a detrimental impact on the signal or SWR. Why yes, it might, or it might not. This can be said of any material. Not being aware of this a long time ago, I built a two meter half-wave vertical dipole by dropping a line of wire into a piece of CPVC and capping it off. My mobile 5/8 wave whip on the car, twelve feet below it, using the same rig has much much better reception and signal than the dipole. I plan to replace that antenna with a similar dipole using 1/2 inch copper tubing. When I nuke the cpvc for one minute, it gets warm to the touch. I don't expect to melt it using my 706, but I do have a couple of repeaters I can't hear from that antenna that I would like to reach. That's an interesting anecdode, but it hardly supports the contention that there's a direct correlation between heating in a microwave oven and detraction of performance of an HF antenna when used as an end insulator. Roy Lewallen, W7EL |
#10
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W9DMK (Robert Lay) wrote:
On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen wrote: It's not clear to me how you correlate how warm something gets in the microwave oven with how much loss it'll incur at the end of an HF antenna. Maybe someone can explain this. Dear Roy, Perhaps that is not the objective, Roy - maybe the rationale' is simply to decide whether or not a particular sample of material is a "high loss" dielectric or not. Is a material that is "high loss" at microwave frequencies always "high loss" at HF? How "high" does the loss have to be in order to detract from an HF antenna's performance when used as an end insulator? When you put an object in the microwave oven for a minute with a glass of water and the temperature rises 10 degrees C, how "high" is the loss? How "high" is the loss at HF? Roy Lewallen, W7EL |
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