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In playing around with some RF beacons I noticed that there is generally just one driven element, with the other elements connected to ground if present. I'm having some trouble wrapping my head around this idea, for example, when connecting a simple transmitter to a half wave dipole one element would be driven and the other would always be connected to ground.

This is contrary to how I believed radio waves were generated, that is, by having alternating currents in different radials. Other designs have a transformer on the output with the secondary connected to the antenna. This makes a whole lot more sense since both elements of a dipole are then driven. So my question is, does it really make a difference if both elements are driven or if one is simply connected to ground and the other swings around it?


This might be where the balanced/unbalanced thing comes in, which I've never been able to wrap my head around?


Something like the Pixie 2 Transceiver for example, which seems to be fairly popular among the DIY QRP crowd.

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A dipole should be driven with a balanced signal or it ceases to become a dipole - my bet is that you are missing some subtlety like a balun made from short pieces of coax. Measuring with a meter is a waste of time of course because, at DC ground will connect to one of the dipole's terminals because of the balun. Only at the proper RF frequency can this be measured.

Regards the comments about not feeding a dipole with a balanced signal, here's what I found below.

Wiki to the rescue. Look at the "Feeding a dipole antenna" section: -

When a balanced antenna is fed with a single-ended line, common mode currents can cause the coax line to radiate in addition to the antenna itself,[11] distorting the radiation pattern and changing the impedance seen by the line. The dipole can be properly fed, and retain its expected characteristics, by using a balun in between the coaxial feedline and the antenna terminals. Connection of coax to a dipole antenna using a balun is described in greater detail below

And another rescuer: -

In Figure 1, a coaxial cable is connected to a dipole antenna. For a dipole antenna to operate properly, the currents on both arms of the dipole should be equal in magnitude. When a coaxial cable is connected directly to a dipole antenna however, the currents will not neccessarily be equal. To see this, note that the current along a transmission line should be of equal magnitude on the inner and outer conductors, as is typically the case. Observe what happens when the coax is connected to the dipole. The current on the center conductor (the red/pink center core of the coax, labeled IA) has no where else to go, so must flow along the dipole arm that is connected to it. However, the current that travels along the inner side of the outer conductor (IB) has two options: it can travel down the dipole antenna, or down the reverse (outer) side of the outer conductor of the coaxial cable (labeled IC in Figure 1).

Figure 1 (as mentioned directly above): -

enter image description here

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  • \$\begingroup\$ So these setups assume you are running into a balun? My antenna tuner for example grounds the coax shield, so a balun would be absolutely necessary? \$\endgroup\$ – s3c Sep 25 '15 at 14:12
  • \$\begingroup\$ @s3c I believe so and one might be at your antenna - can you post a picture. \$\endgroup\$ – Andy aka Sep 25 '15 at 14:14
  • \$\begingroup\$ My main radio does use one (because I was told to), my question is more general. It is common to see designs where the coax is grounded and the inner element is driven. This doesn't make sense to me, since you don't have two opposing fields in such a design. Unless I'm missing something else? \$\endgroup\$ – s3c Sep 25 '15 at 14:37
  • \$\begingroup\$ My answer is still the same - I don't believe so but maybe someone can answer who recognizes that a normal dipole turns into some other mode of operation when driven unbalanced. \$\endgroup\$ – Andy aka Sep 25 '15 at 14:41

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