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I recently built a TV twinlead slim-jim antenna. This isn't at all suitable for outdoor use, but I could mount it in a plastic pipe and stick it up on my roof. I've heard that PVC degrades 144 MHz signals. Does ABS cause significant interference/degradation of a 2m signal? (For that matter, does PVC really cause a problem?) |
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Well, there's two things at play here - but the short answer is that PVC is just fine. First, there's going to be some teeny tiny attenuation of the signal depending on the thickness of the PVC and the power of the signal. This isn't going to be a big deal though. Second, the insertion of the antenna into the PVC will change the velocity factor of the radio waves passing through it - so you'll find that an antenna that was tuned resonant to a particular frequency will shift slightly when inserted into the tube. I've built several twinlead j-poles and housed them inside PVC with no issues, but they should be tuned with the PVC housing in mind. |
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I have a few friends who use twin-lead j-pole antennas as mobile antennas contained within white PVC pipe and seem to have no problem at 6, 2, or 440. The best application seems to be within a pick-up truck bed. |
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PVC or ABS should both have little impact, but some, so tune the antenna with everything in place to make sure you compensate for any effect. I put a 1296 MHz loop yagi in 4" PVC and it didn't seem to affect it at all. Most modern paints have no effect, or again, very little. Again, tune it with everything done you're going to do. Old paints used to have lead or carbon in them. I once had black paint that was very conductive and could not be used on radomes (plastic antenna covers). For PVC, use the gray electrical stuff, it is already made for sunlight and UV exposure. Here's a cute trick - whatever you want to use around an antenna, put a piece of it in the microwave, with a cup of water. Run it for a while and see if it gets at all warm. If it stays cool, it will probably have no effect on your antenna. -Dan, KW2T |
