I know this would not have an effect on f/s, but what would making a stranded coper mast out of 3m long 1/4 inch copper tubing tied together in parralel making a 3" dia. x 3m mast have on the bandwidth?
I'm trying to come up with a part 15 compliant setup that has wide enough bandwidth to work with Chris Cuff's C-QuAM transmitters.
A 3-m tall radiator with an outer diameter of 3 inches and 28 ohms of coil/ground loss has a 3 dB r-f bandwidth of nearly 22 kHz for a 1620 kHz carrier.
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I asked this some time in the past, and Rich did some calculations... You would need a very wide antenna to make a large difference (I forget the exact size).
3db @ 22kHz? We only need 10 kHz max for AMS operation and NRSC is 9 or 11 khz forget which.
Thank You,
Rev. Robert P. Chrysafis
Universal Life Ministries
http://www.ulc.org
Moderator Hunterdonfree
http://groups.yahoo.com/group/hunterdonfree
Don't forget that an AM r-f bandwidth of 22 kHz produces a received audio bandwidth only one-half of that (assuming that the receiver system can pass that full 22 kHz of r-f bandwidth in the first place).
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so when NRSC speaks of 10khz they actually mean a 22khz RF bandwidth 10khz audio bandwidth. ok. then yes i would be looking to achieve about 20khz RF bandwidth. I was talking stranded copper. bundling 1/4 inch diameter tubes to make a 3 inch diameter tube each one has it's own surface which means it would have 3 times or more surface area than just a 3 inch diameter tube.
Thank You,
Rev. Robert P. Chrysafis
Universal Life Ministries
http://www.ulc.org
Moderator Hunterdonfree
http://groups.yahoo.com/group/hunterdonfree
I'm not entirely sure, but I think that with the skin effect, only the ones on the outside of the bundle would actually radiate, though.
But the good news to that would be you could just use the outer layer of tubes and bundle them around a few wooden disks. Maybe solder the tubes together with plumbing solder and it'd be considerably tougher/stronger than a simple cylinder.
Less expensive yet would be to leave some space between the tubes and make them into a cage, but I think those are usually fed from the top with a shielded coax brought up the center and I'm not sure how that would be viewed for the 3 meters total rule. To my way of thinking it'd be a 3 meter antenna, since the 3 M of coax going up the center isn't going to give the same advantage as a long ground wire to a vertical would, and it's one 3 M long unit total.. But I'm not an FCC inspector.
But I *think* a 3 inch wide "cage" might have similar bandwidth characteristics to a 3 inch solid (or bundled tubes) antenna, if there are enough "bars" to the cage. Not sure how many that takes, since I've just looked at the designs out of general interest in antennas, didn't look into them like I would if I were considering building one.
Now *if* a shielded coax running up the inside of a cage antenna was allowable, there would be some interesting possibilities to top feeding it, like having the inductor inside the cage near the top and the transmitter at the bottom inside the cage and grounded directly into the dirt just like the wires/tubes/pipes of the cage. Not sure how such a setup would be viewed in terms of the 3 M total, though. But it'd be attractive from a durablity and vandalism-proofing perspective even if it didn't actually work any better than a base loaded simple vertical. If the audio and power wires were buried, it'd also be pretty lawnmower and weedeater proof, and the "bars" of the cage could maybe be soldered directly to the underground radials? Just "thinking out loud" a bit.
In any case.. neat idea, Rev Chrysafis.
Daniel
by MRAM 1500 kHz
I made a 50 foot vertical used on the 160 meter ham band out of sections of aluminum down spout pipe.
I figured that most antennas are made from aluminum tubing so why not? And, with a cross section of about 3 inches, it should give plenty of capacitance which is a plus, reducing the needed inductance of a loading coil.
For the Part 15 antenna, one ten foot section would be plenty light enough and fairly ridgid also. My 50 footer was guyed at the top and middle and held up longer than I expected. So, one ten foot section set in a plastic bucket of sand should work although there's probably lots of better ways to secure the base.
If you're looking for a light weight, large cross section radiator 10 feet long, this may be the ticket!
Just ran across this post from a few years ago.
Now, what if you turned the 3" dia. downspout tubing into a slotted radiator. How would you build and connect that for AM BCB? Since slotted radiators are suppose to emanate signal perpendicular to the tube, does that mean it should be oriented horizontally?
What determines the number, separation, and size of the slots, and how are they oriented, e.g., slots facing up, down, to a side?