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Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
ok, so this may be unusable, but under my parents roof any HF antenna I make has to be out of the way and look neat, while being on a budget... I tried a dipole, but my parents hate it, and it needed to get higher up anyways (and it can go pretty high, it's just that it wouldn't be safe for me to install it as high as my area permits, while making it relatively inconspicuous... then a few moments ago it occurred to me: our Sport Court has a large light pole, mounted to a concrete base - I first thought of using it as a mast for an inverted V, but that would not make my parents happy; then I thought about stringing the dipole from it to a few nearby objects, but those other endpoints are too close to power lines... then I thought, what if I used the actual pole as part of the antenna, and make some small additions to adjust it? - it forms a pseudo-"inverted L" - it gets a good 20-30 feet off of the ground, I don't know the exact height off the top of my head, but we should still have records from the installation...
this could simply be a bad idea, but I want to explore all of my options...
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
GeordieBoy wrote ...
From a technical viewpoint: The lightpost will be solidly grounded for electrical safety so you won't be able to make it radiate efficiently.
From a practical viewpoint: Modifying or tampering with local council owned equipment is likely to end you up in legal bother!
-Richie,
I should have realized it would be grounded, maybe I can just use it as a mast or something in the end... it would also make a nice cable runner!
but it is not a city light pole, it is the light pole for my family's Sport Court in our Back Yard... it is privately owned, and maintained...
I might try the Inverted V from it as an Apex but my parents will likely just freak out and make me take it down... maybe I'll be able to have it up long enough to make my first HF Contact
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
Also it is worth noting that if you intend to transmit any significant power from an antenna incorporating the metal lamp post, you may end up coupling a lot of RF onto the mains wiring feeding the post. I believe a 1/4 whip antanna causes a current to flow in the reflection area directly below the base of the antenna? The Radio Hams will know more about whether this is true or not!
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
GeordieBoy wrote ...
Also it is worth noting that if you intend to transmit any significant power from an antenna incorporating the metal lamp post, you may end up coupling a lot of RF onto the mains wiring feeding the post. I believe a 1/4 whip antanna causes a current to flow in the reflection area directly below the base of the antenna? The Radio Hams will know more about whether this is true or not!
-Richie,
I actually think you are right, however assuming said currents aren't induced at the base of the post from the antenna, it might be fine, as the circuit to control the lamps are, in fact, at the very base with a switch, but this may not be enough protection... yet, assuming the post is grounded, which as it was pointed out likely is due to safety concerns, then the power wires on the inside should be shielded to a decent extent assuming the post itself is not used as a designed part of the antenna - in the end it likely would still allow some RF into the lines, but considering the circumstances I doubt it would be much, especially after considering the fact that the lamps are on a dedicated circuit
I might try a whip, but I think I'll consider all of the details a little more first.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Another option is the temporary aerial like those army rigs where a weighted long wire is thrown up into the branches of a convenient tree., and then pulled down again when you've finished. And you can drive in an earth spike with a mallet just beneath the antenna.
Electrical and legal problems aside, you may be able to shunt feed it. Shunt feeding is typically used on antenna towers on the low bands, but people have successfully loaded up flag poles and the like with this method. Finding the points to feed it to find resonance is a LOT easier if you have an antenna analyzer, but if you don't have one you can also model it or use trial and error. The basic idea is to attach your feedline to 2 points on the mast (hose clamps?) and slide them around until you get a good SWR and (hopefully) a good radiation pattern.
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HF Antenna thought... maybe use a light post?
