Care and feeding of beverage / longwire antennas

[ChrisSmolinski]

This is the approach I use for feeding my Beverage antennas. Some modifications are necessary depending on each situation, so I'll explain the thought process. Starting at the radio end...

Coax from the radio (which itself may or may not be grounded, but probably should be) runs out the shack and down to the ground. Here it goes through one of those ubiquitous cable TV grounding blocks, which is connected to a ground rod. I use RG-6 coax, so this is cheap and easy. If you use coax with hateful UHF/PL-259 connectors, this is more expensive and difficult, but can be done.

From there my coax runs in underground conduit to the feedpoint of the Beverage antenna. Obviously it's not necessary to bury the cable, but it both keeps it out of sight and out of the way, and potentially reduces RFI issues as the earth surrounding the coax can attenuate currents trying to flow on the coax shield.

If your feedpoint is at the house, then of course this cable run is not needed.  In some cases, I have long coax runs that are grounded at two or more locations in the middle of the run.

At the feedpoint, I then ground the coax shield again where it attaches to the transformer to the antenna. One end of the primary winding gets grounded as well via this.

The secondary of the transformer also has one end of the winding grounded, the other end goes to the antenna.  Note that there are two ground rods here, the primary and secondary windings are not directly shorted to each other.  The assumption here is that the primary and secondary windings of the transformer are isolated, ie if measured with an ohm meter there is no continuity. If they are not isolated, then of course only one ground rod / connection is needed.

Assuming they are isolated, it is critical that the other wire on the secondary be grounded and not left floating. Just today I noticed that the ground on the secondary of the transformer feeding my 300 ft south directed antenna had some loose. (This antenna feeds the R71/A in my basement workshop which I use infrequently which is probably why I not notice a problem earlier) Before repairing it, I took signal strength readings across the MW band. After repairing it, I checked the same stations again, and signal strengths were generally 10 to 30 dB higher. Stations that were not audible at all were coming in fairly well. Without the ground connection, current cannot flow in the secondary and there is no real transformer action, most likely just capacitive coupling between the secondary and primary windings.

At the far end of the antenna, it is terminated through a resistor to ground. The exact value depends on the antenna and is usually determined experimentally using a VNA / Antenna Analyzer, which also is used to determine the transformer ratio. Often the termination resistor ends up in the 200-500 ohm region, and the transformer ratio is that which is required to match said impedance to the coax cable. When properly matched, the SWR is usually fairly flat over the entire spectrum. Note that in contrast with transmitting antennas, perfect matches with an SWR of 1 are not required. An SWR of 2 or even a bit more is perfectly fine. Close enough is good enough for receiving antennas.

The purpose of the termination resistor is to improve directivity, and help reject signals from the opposite direction. If the antenna is not terminated, those signals (which arrive at the feedpoint end of the antenna) will be reflected at the far end, and then travel back down the antenna to the feedpoint, and then to the receiver. If the antenna is terminated, they will instead be absorbed instead of reflected. Of course if you want to pick up signals in both directions, then leave the termination resistor off.

[Rizla]

I really appreciate this post, some of the best first-hand stuff I've found on the beverage antennas (there's a lot of good stuff, of course, but some of it is "bibliographic echo" so to speak)... I have a place to try some ideas (one of these days), and you basically summed it up, thank you.

Now here's a question. I think in the old docs by Mr. Beverage himself or the ARRL, people have transmitted with these. Surely not optimal. Have you heard of someone doing this successfully? I know there are issues with transmit big enough to drive an aircraft carrier through, so to speak.

[Ray Lalleu]

Now here's a question. I think in the old docs by Mr. Beverage himself or the ARRL, people have transmitted with these. Surely not optimal. Have you heard of someone doing this successfully? I know there are issues with transmit big enough to drive an aircraft carrier through, so to speak.

Don't know. But the Beverage antenna has low efficiency : not an issue for receiving, as that's a low noise antenna, thanks to directive pattern. Also, transmitting with a long wire at very low height means serious security hazards.
Better way, if you have enough land : look for the rhombic antennas.

At the quick and dirty level, I remember the antennas used by the soviet army for radios in war shelter, still available as surplus now, looking as strange packs of wires, not clear how to place them for real use. Several types for several SW ranges, but I can't remember any useful word to find that on Internet. A detail : the end of the antenna is divided into 3 short wires to leave down on the ground. And the direction for  the troopers should be towards the rear, towards their headquaters.