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Dipole
- Thread starter SOA527
- Start date
Ok, ive been reading a lot of the threads on dipoles, and am thinking about setting one up. Yeah, ciuld put it in the attic, but could string it in the trees, weve got a lot! Is tension or droop an issue for resonance? Im thinking about effect tuning fork (fixed) has upon, lets say, guitar string(variable) . Or is this really an issue. Also, most models ive seen use the ends wrapped in aloop for attachment..........where does the "real" antenna start and end? Maybe after you make it wrap back on itself you leave a pigtail to trim ??? Ask, and ye shall learn.
You will learn soon enough everything affects SWR. Experimenting is half the fun. If you know the exact frequency or channel you like to operate cut the dipole for the lowest SWR. All other channels will have to compromise, the thicker the wire the broader the bandwidth. An antenna tuner will help some. Inverted "V" is what I used in an attic about 50 ft at the highest point. Not the best setup but it works for me.
Tension on a guitar/piano/harp string is vitally important, but there we're talking about audio frequencies. Radio frequency is a whole nother barrel of kettles .. or something like that. About the only problem you might have with a dipole attached to trees on either end and that moves around in the wind would be small changes on the meter as the antenna moves. Wind stops, everything's back to where it was.
You CAN use springs to minimize things -- the ARRL Antenna Book is something you should get for other suggestions on wire antennas.
You CAN use springs to minimize things -- the ARRL Antenna Book is something you should get for other suggestions on wire antennas.
One end have fixed/immovable; the other on a rope with a weight to keep it taught and to take it down.
He's not wrong but it wouldn't be all that noticeable unless he built an 11 meter cage diople....I've never saw one if those.
Didn't say he is wrong, but with wire dipoles,heavier wire can increase bandwidth some but it is very minimal. If it really was significant, you have people using 4/0 wire.He's not wrong but it wouldn't be all that noticeable unless he built an 11 meter cage diople....I've never saw one if those.
I agree. I wasn't trying to put words in your mouth. Just throwing in my 2 cents.
Yup, guess that gets it.....just dont think of resonance and impedance as the same thing. Impedance to me is resistance, where resonance is more about vibration at a frequency.....thinking reed meters ive used. Maybe my thinking is skewed a bit because of so little radio knowledge, cos now looking at audio wave input on a wire, changing wire length would, i guess, change its impedance. Time to do some reading, maybe. Am i in the ballpark tho??
REACTANCE is the opposition to current flow in an RF circuit. It can be positive (a net INDUCTIVE REACTANCE XL) or negative (net CAPACITIVE REACTANCE XC). The L and C should be subscripts but how to write them on a computer is beyond me right now.
IMPEDANCE (Z) is the vector sum of the circuit's reactance and resistance.
RESONANCE is the condition in which a circuit's inductive reactance and capacitive reactance are equal (but with opposite polarity). This cancels the reactances, making XC = XL; Z=zero, and at this point, the only opposition to current flow is the DC resistance.
HOWever, comma, for any combination of capacitance and inductance, resonance will occur at only ONE frequency. Move either higher or lower in frequency and the circuit is no longer resonant.
Those reed meters you referred to show MECHANICAL resonance: a line of what look like oboe reeds, with a meter scale underneath them, indicating the center reed as "60 Hz", for example, with the one on the far left labelled "55 Hz" and the far right reed labelled "65 Hz". If your power line frequency is 60Hz, the center reed will be vibrating the most, with the others tapering off toward either end. It would be very difficult to apply this design to RF circuits.